@article{fu_horton_ren_heitman_2023, title={An Unsaturated Hydraulic Conductivity Model Based on the Capillary Bundle Model, the Brooks-Corey Model and Waxman-Smits Model}, volume={59}, ISSN={["1944-7973"]}, url={http://dx.doi.org/10.1029/2022wr034186}, DOI={10.1029/2022WR034186}, abstractNote={Abstract Soil unsaturated hydraulic conductivity ( K ), which depends on water content ( θ ) and matric potential ( ψ ), exhibits a high degree of variability at the field scale. Here we first develop a theoretical hydraulic‐electrical conductivity ( σ ) relationship under low and high salinity cases based on the capillary bundle model and Waxman and Smits model which can account for the non‐linear behavior of σ at low salinities. Then the K ‐ σ relationship is converted into a K ( θ , ψ ) model using the Brooks‐Corey model. The model includes two parameters c and γ . Parameter c accounts for the variation of the term ( λ + 2)/( λ + 4) where λ is the pore size distribution parameter in the Brooks‐Corey model, and the term m‐n where m and n are Archie's saturation and cementation exponents, respectively. Parameter γ is the sum of the tortuosity factor accounting for the differences between hydraulic and electrical tortuosity and Archie's saturation exponent. Based on a calibration data set of 150 soils selected from the UNSODA database, the best fitting log( c ) and γ values were determined as −2.53 and 1.92, −4.39 and −0.14, −5.01 and −1.34, and −5.79 and −2.27 for four textural groups. The estimated log 10 ( K ) values with the new K ( θ , ψ ) model compared well to the measured values from an independent data set of 49 soils selected from the UNSODA database, with mean error (ME), relative error (RE), root mean square error (RMSE) and coefficient of determination ( R 2 ) values of 0.02, 8.8%, 0.80 and 0.73, respectively. A second test of the new K ( θ , ψ ) model using a data set representing 23 soils reported in the literature also showed good agreement between estimated and measured log 10 ( K ) values with ME of −0.01, RE of 9.5%, RMSE of 0.77 and R 2 of 0.85. The new K ( θ , ψ ) model outperformed the Mualem‐van Genuchten model and two recently published pedo‐transfer functions. The new K ( θ , ψ ) model can be applied for estimating K under field conditions and for hydrologic modeling without need for soil water retention curve data fitting to derive a K function.}, number={6}, journal={WATER RESOURCES RESEARCH}, publisher={American Geophysical Union (AGU)}, author={Fu, Yongwei and Horton, Robert and Ren, Tusheng and Heitman, Joshua}, year={2023}, month={Jun} }
 @article{sun_xiao_li_yu_kidron_heitman_2023, title={Direct evidence and mechanism for biocrusts-induced improvements in pore structure of dryland soil and the hydrological implications}, volume={623}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2023.129846}, abstractNote={As a crucial living skin inhabiting the soil-atmosphere interface, biocrusts play a vital role in various soil properties and processes, especially surface soil pore structure and soil pore-related hydrological processes, such as infiltration and evaporation. However, it remains unclear how biocrusts affect pore structure in the micrometric point of view. In this study, X-ray computed tomography and image analysis were employed to quantify the differences in soil pore structure between bare soil and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) at 0–50 mm depth. Three-dimensional images were segmented and analyzed to assess morphological and geometrical properties, such as porosity, pore volume, degree of anisotropy, Euler number, pore shape, pore connectivity, and pore tortuosity. Our results showed that the porosity of three types of biocrusts was, on average, 100% higher than bare soil, and the porosity ranked in order of moss crusts > mixed crusts > cyanobacterial crusts > bare soil. In comparison to bare soil, pore surface area density, mean pore volume, and node density of biocrusts were increased by 45%, 422%, and 52% on average, respectively. Biocrusts had larger fractal dimensions but lower degrees of anisotropy, mean tortuosity, and Euler number, which indicates the pore structure of biocrust became more complex and stable with higher connectivity compared to bare soil. Additionally, elongated pores had the largest contribution to porosity, and these pore proportions were significantly higher in biocrusts than bare soil. More importantly, the pore network model and network analysis revealed that biocrusts have a higher connected porosity (17% vs. 4%), connected porosity/isolated porosity (11.7 vs. 0.6), average coordination number (8 vs. 5), and number of channels (14,480 vs. 807), but a lower average channel length (2.7 vs. 3.8 mm), which indicates that the physical and topological structures of pore network in biocrusts were reconfigured and exhibited a better pore network connectivity. Moreover, the biocrusts increased soil water holding capacity by 87% on average, but decreased saturated hydraulic conductivity by 55% as compared to bare soil. From the reshaped pore structure, improved soil water holding capacity, and decreased infiltrability of the biocrusts in comparison to bare soil, we conclude that biocrusts play a vital role in surface soil water balance, which subsequently affect surface hydrological processes (e.g., runoff generation and evaporation) in drylands.}, journal={JOURNAL OF HYDROLOGY}, author={Sun, Fuhai and Xiao, Bo and Li, Shenglong and Yu, Xingxing and Kidron, Giora J. and Heitman, Joshua}, year={2023}, month={Aug} }
 @article{fu_liu_lu_horton_ren_heitman_2023, title={Estimating soil water retention curves from thermal conductivity measurements: A percolation-based effective-medium approximation}, volume={624}, ISSN={["1879-2707"]}, url={http://dx.doi.org/10.1016/j.jhydrol.2023.129898}, DOI={10.1016/j.jhydrol.2023.129898}, abstractNote={A soil water retention curve (SWRC) describes the relationship between soil water content (θ) and suction (h, also the absolute value of pressure head). Earlier work indicated that correlations existed between the percolation-based effective medium approximation (P-EMA) thermal conductivity (λ) model parameters and soil hydraulic properties. In this study, the critical water content (θc) of the P-EMA model was related to the pore size distribution parameter (m) of the van Genuchten model, water content at the inflection point of a SWRC (θi) and hydraulic continuity water content (θhc). And a pedo-transfer function was established to estimate the van Genuchten model parameter α from soil properties and P-EMA parameters. Based on these relationships, three approaches were developed to estimate the van Genuchten models parameters from λ(θ) measurements, porosity, sand and clay contents. The three approaches were then validated on six independent soils, and results showed that all of the approaches estimated θ well at selected h values, with the average root mean square errors from 0.025 to 0.029 cm3 cm−3, the average mean relative absolute errors ranging from 0.111 to 0.157, and the average Akaike Information Criterion from −18.3 to −16.2. Two new approaches outperformed the original Fu et al approach but with fewer input parameters (no need for organic carbon content), thus also facilitating their broader application.}, journal={JOURNAL OF HYDROLOGY}, publisher={Elsevier BV}, author={Fu, Yongwei and Liu, Lin and Lu, Yili and Horton, Robert and Ren, Tusheng and Heitman, Joshua}, year={2023}, month={Sep} }
 @article{fu_jones_horton_heitman_2023, title={Excluding quartz content from the estimation of saturated soil thermal conductivity: Combined use of differential effective medium theory and geometric mean method}, volume={342}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2023.109743}, abstractNote={Saturated soil thermal conductivity (λsat) is the maximum soil thermal conductivity value of a given soil. Although it can be determined accurately with a heat pulse sensor, there are challenges to prepare fully saturated soil samples. Numerous models have been developed to estimate λsat, and among these, the geometric mean method (GMM) generally performs well. The GMM requires soil mineral composition or quartz content information, which is unavailable for most soils. Earlier studies commonly used assumed that quartz content (fquartz) was equal to sand content (fsand) or to 0.5 × fsand, which led to significant λsat estimation errors especially on coarse-textured soils. We derived a novel method to estimate λsat from soil porosity (ϕ) based on a combination of the GMM and differential effective medium theory (DEM). The new DEM-GMM approach has a single parameter, cementation exponent (m). Using a calibration dataset of 43 soils, we determined best fit m values for soils in three groups: 1.66 for Group I (fsand < 0.4), 1.62 for Group II (0.4 <= fsand < 1) and m = -1.34ϕ+1.70 for Group III (fsand = 1). Using best fit m values for different groups, the new model can estimate λsat values from ϕ. Independent validation results on another 46 soils showed that the new model outperformed the GMM method with the assumption that fquartz = fsand or fquartz = 0.5 × fsand. The mean RMSE, Bias and R2 values of the DEM-GMM approach were 0.202 W m−1 K−1, 0.013 W m−1 K−1 and 0.89, respectively, and corresponding values of the GMM with the two assumptions were 0.295 and 0.476 W m−1 K−1, 0.056 and -0.28 W m−1 K−1, 0.80 and 0.82, respectively. The robust performance of the DEM-GMM approach suggests that it can be incorporated into thermal conductivity models to accurately estimate the thermal conductivity of unsaturated soils.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Fu, Yongwei and Jones, Scott and Horton, Robert and Heitman, Joshua}, year={2023}, month={Nov} }
 @article{kranz_mclaughlin_amoozegar_heitman_2023, title={Influence of compost amendment rate and level of compaction on the hydraulic functioning of soils}, volume={3}, ISSN={["1752-1688"]}, url={https://doi.org/10.1111/1752-1688.13119}, DOI={10.1111/1752-1688.13119}, abstractNote={Abstract There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity ( K s ) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m 3 /m 3 , and the sandy loam was further tested at high (0.55 m 3 /m 3 ) and low (0.4 m 3 /m 3 ) porosities. The K s and water retention data were then used to model infiltration with HYDRUS‐1D. With increasing compost amendment rate, K s and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve K s rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant‐available, and unavailable water) depended on texture, with only the highest compost rates increasing plant‐available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted.}, journal={JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION}, author={Kranz, Christina N. and McLaughlin, Richard A. and Amoozegar, Aziz and Heitman, Joshua L.}, year={2023}, month={Mar} }
 @misc{ile_mccormick_skrabacz_bhattacharya_aguilos_carvalho_idassi_baker_heitman_king_2023, title={Integrating Short Rotation Woody Crops into Conventional Agricultural Practices in the Southeastern United States: A Review}, volume={12}, ISSN={["2073-445X"]}, url={https://www.mdpi.com/2073-445X/12/1/10}, DOI={10.3390/land12010010}, abstractNote={One of the United Nations Sustainable Development Goal’s (SDGs) aims is to enhance access to clean energy. In addition, other SDGs are directly related to the restoration of degraded soils to improve on-farm productivity and land management. Integrating Short Rotation Woody Crops (SRWC) for bioenergy into conventional agriculture provides opportunities for sustainable domestic energy production, rural economic development/diversification, and restoration of soil health and biodiversity. Extensive research efforts have been carried out on the development of SRWC for bioenergy, biofuels, and bioproducts. Recently, broader objectives that include multiple ecosystem services, such as carbon sequestration, and land mine reclamation are being explored. Yet, limited research is available on the benefits of establishing SRWC on degraded agricultural lands in the southeastern U.S. thereby contributing to environmental goals. This paper presents a literature review to (1) synthesize the patterns and trends in SWRC bioenergy production; (2) highlight the benefits of integrating short rotation woody crops into row crop agriculture; and (3) identify emerging technologies for efficiently managing the integrated system, while identifying research gaps. Our findings show that integrating SRWC into agricultural systems can potentially improve the climate of agricultural landscapes and enhance regional and national carbon stocks in terrestrial systems.}, number={1}, journal={LAND}, author={Ile, Omoyemeh J. and McCormick, Hanna and Skrabacz, Sheila and Bhattacharya, Shamik and Aguilos, Maricar and Carvalho, Henrique D. R. and Idassi, Joshua and Baker, Justin and Heitman, Joshua L. and King, John S.}, year={2023}, month={Jan} }
 @article{mathers_heitman_huseth_locke_osmond_woodley_2023, title={No-till imparts yield stability and greater cumulative yield under variable weather conditions in the southeastern USA piedmont}, volume={292}, ISSN={["1872-6852"]}, DOI={10.1016/j.fcr.2023.108811}, abstractNote={With projected increases in global temperatures and changes in regional climate, understanding the impact of soil management choices on yield stability is critical for farmer decision-making and agricultural resiliency. No-till and conservation tillage have had variable yield effects depending on crop and location, requiring long-term system-specific studies to gauge potential benefits. Yield and weather data from a 28-year tillage study in the southeastern U.S. piedmont region were analyzed to determine the effect of various conservation tillage practices on maize and soybean productivity and stability under a variety of growth conditions. Growing seasons were grouped by soil moisture and temperature during crop growth stages, and mean crop yields and yield coefficient of variation for the tillage treatments were calculated within the year clusters. Probability density estimates were also used to predict the likelihood of obtaining yields at low and high percentiles. No-till and conservation tillage increased maize yields 42–93% and no-till decreased coefficient of variation of maize yields when soil moisture was low by 10–32%, but had a less pronounced effect on soybean yields. However, the probability of reaching the 90th yield percentile was greater in no-till than conventional tillage in both maize and soybean, by 15% and 10%, respectively. Yield differentiation occurred early in the study, before there was likely substantial differentiation of soil properties from tillage treatments. Previous reports from the site have likewise indicated little differentiation in soil health between tillage systems over the life of the study. Results suggest that surface residue management may be an important driver of system performance, possibly more so than overall soil health.}, journal={FIELD CROPS RESEARCH}, author={Mathers, Cara and Heitman, Joshua and Huseth, Anders and Locke, Anna and Osmond, Deanna and Woodley, Alexander}, year={2023}, month={Mar} }
 @article{fu_ghanbarian_horton_heitman_2023, title={Robust calibration and evaluation of a percolation-based effective-medium approximation model for thermal conductivity of unsaturated soils}, volume={438}, ISSN={["1872-6259"]}, DOI={10.1016/j.geoderma.2023.116631}, abstractNote={Thermal conductivity (λ) is a property characterizing heat transfer in porous media, such as soils and rocks, with broad applications to geothermal systems and aquifer characterizations. Numerous empirical and physically-based models have been developed for thermal conductivity in unsaturated soils. Recently, Ghanbarian and Daigle (G&D) proposed a theoretical model using the percolation-based effective-medium approximation. An explicit form of the G&D model relating λ to water content (θ) and equations to estimate the model parameters were also derived. In this study, we calibrated the G&D model and two widely applied empirical λ(θ) models using a robust calibration dataset of 41 soils. All three λ(θ) model performances were evaluated using a validation dataset of 58 soils. After calibration, the root mean square error (RMSE), mean absolute error (MAE) and coefficient of determination (R2) of the G&D model were 0.092 W−1 m−1 K−1, 0.067 W−1 m−1 K−1 and 0.97, respectively. For the two empirical models, RMSEs ranged from 0.086 to 0.096 W−1 m−1 K−1, MAEs from 0.063 to 0.071 W−1 m−1 K−1, and R2 values were about 0.97. All three metrics indicated that calibration improved the performance of the G&D model, and it had an accuracy similar to that of the two empirical λ(θ) models. Such a robust performance confirmed that the theoretically-based G&D model can be applied to study soil heat transfer and potentially other related fields.}, journal={GEODERMA}, author={Fu, Yongwei and Ghanbarian, Behzad and Horton, Robert and Heitman, Joshua}, year={2023}, month={Oct} }
 @article{xia_heitman_shi_2023, title={Soil macroporosity modulates the extent of negative microbial associations during organic substance decomposition}, volume={187}, ISSN={["1879-3428"]}, DOI={10.1016/j.soilbio.2023.109202}, abstractNote={Microbial species interactions are expected to influence the community-level properties, such as the production of extracellular enzymes and the degradation of organic substances. This work examined how microbial diversity, composition and the overall sign of microbial associations were altered with soil texture and structure following the amendment of organic substances. Two sets of microcosms (1:100 and 1:1) of a 4 × 3 factorial design were constructed, with four artificial textural classes (a sandy loam, two loams, and a (silty) clay loam) and three organics (TSB, tryptic soy broth; CA, a mixture of cellulose and humic/fulvic acids; BS, barley straw). As the ‘microbial inoculant’, an agricultural soil was added to the 1:100 and 1:1 microcosms at 1% and 50%, respectively. A few of microbial taxa were specifically enriched after soil addition of TSB, CA, or BS, but distributions across textural classes were inconsistent between microcosms or between organic amendments. Regardless, top abundant bacterial and fungal OTUs were overall negatively associated, suggesting that microbial competition for the shared resource dominated the decomposition of both simple and complex organics. Microbial associations were also modified by soil pore size distribution (PSD), being fewer negative (or more positive) in soils of greater macroporosity than in soils of lower macroporosity. The PSD-based differences in microbial associations were coordinated with PSD-based differences in the activities of exoglucanase and β-glucosidase in TSB-amended soils or soil respiration characteristics in CA-amended soils. Our results provide new insight into how soil structure regulates microbial interactions and, accordingly, the degradation of organic matter.}, journal={SOIL BIOLOGY & BIOCHEMISTRY}, author={Xia, Qing and Heitman, Joshua L. and Shi, Wei}, year={2023}, month={Dec} }
 @article{heitman_kool_carvalho_2023, title={Soil management considerations for water resiliency in a changing climate}, volume={8}, ISSN={["1435-0645"]}, DOI={10.1002/agj2.21425}, journal={AGRONOMY JOURNAL}, author={Heitman, Joshua L. and Kool, Dilia and Carvalho, Henrique D. R.}, year={2023}, month={Aug} }
 @article{camacho_faundez-urbina_amoozegar_gannon_heitman_leon_2023, title={Subsurface Lateral Solute Transport in Turfgrass}, volume={13}, ISSN={["2073-4395"]}, url={https://doi.org/10.3390/agronomy13030903}, DOI={10.3390/agronomy13030903}, abstractNote={Turfgrass managers have suspected that runoff-independent movement of herbicides and fertilizers is partially responsible for uneven turfgrass quality in sloped areas. We hypothesized that subsurface lateral solute transport might explain this phenomenon especially in areas with abrupt textural changes between surface and subsurface horizons. A study was conducted to track solute transport using bromide (Br−), a conservative tracer, as a proxy of turfgrass soil inputs. Field data confirmed the subsurface lateral movement of Br− following the soil slope direction, which advanced along the boundary between soil horizons over time. A model based on field data indicated that subsurface lateral movement is a mechanism that can transport fertilizers and herbicides away from the application area after they have been incorporated within the soil, and those solutes could accumulate and resurface downslope. Our results demonstrate that subsurface lateral transport of solutes, commonly ignored in risk assessment, can be an important process for off-target movement of fertilizers and pesticides within soils and turfgrass systems in sloped urban and recreational landscapes.}, number={3}, journal={AGRONOMY-BASEL}, author={Camacho, Manuel E. and Faundez-Urbina, Carlos A. and Amoozegar, Aziz and Gannon, Travis W. and Heitman, Joshua L. and Leon, Ramon G.}, year={2023}, month={Mar} }
 @article{carvalho_aguilos_ile_howard_king_heitman_2023, title={Water use of short-rotation coppice American sycamore (Platanus occidentalis L.) for bioenergy during establishment on marginal land in the North Carolina Piedmont}, volume={276}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2022.108071}, abstractNote={American sycamore (Platanus occidentalis L.) is a hardwood species that can be integrated into short-rotation coppice (SRC) production systems for bioenergy in the southeastern USA. Due to high growth rates and low input requirements, sycamore is regarded as a promising second-generation bioenergy woody crop suitable for degraded or marginal lands. However, little is known about sycamore water use for the conditions of North Carolina (NC), especially during the establishment year when trees are most sensitive to soil water deficits. We evaluated energy fluxes and actual crop evapotranspiration (ETc act) rates of sycamore SRC during the establishment year on marginal land in the Piedmont physiographic region of NC. Our overall goal was to better understand the factors controlling the evaporative demand of sycamore and its sensitivity to drought stress during establishment. Total ETc act was 482 mm, which was 95% of the total rainfall at the site. ETc act rates increased with precipitation and with tree development, reaching a maximum of 5.7 mm d−1. Although severe water stress was not observed during the study period, a moderate drought occurred from mid-August to mid-September, during which a 13-day drying cycle caused ETc act rates to decrease by 30%. The sycamore SRC transitioned from an “energy-limited” to a “water-limited” ETc act regime when water content in the upper 5 cm of soil was about 0.10 m3 m−3, indicating that the sycamore field relied on water available within the upper soil layers. Measurements suggested that trees may not yet have developed a root system sufficient to sustain transpiration during dry spells and that water use of the sycamore field was highly coupled to precipitation during the establishment year.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Carvalho, Henrique D. R. and Aguilos, Maricar M. and Ile, Omoyemeh J. and Howard, Adam M. and King, John S. and Heitman, Joshua L.}, year={2023}, month={Feb} }
 @article{carvalho_howard_amoozegar_crozier_johnson_heitman_2023, title={Water vapor transport through bioenergy grass residues and its effects on soil water evaporation}, volume={10}, ISSN={["1539-1663"]}, DOI={10.1002/vzj2.20282}, abstractNote={Abstract Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in “marginal” lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m −2 , 24 kg m −3 , and 1006 kg m −3 , respectively, giving a porosity of 0.98 m 3 m −3 . A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m −2 was 1.6 mm s −1 . During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a “critical” residue load (∼1.0 kg m −2 ) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining “critical” loads for different residue types is a knowledge gap that merits further research.}, journal={VADOSE ZONE JOURNAL}, author={Carvalho, Henrique D. R. and Howard, Adam M. and Amoozegar, Aziz and Crozier, Carl R. and Johnson, Amy M. and Heitman, Joshua L.}, year={2023}, month={Oct} }
 @article{kranz_mclaughlin_heitman_2022, title={Characterizing Compost Rate Effects on Stormwater Runoff and Vegetation Establishment}, volume={14}, ISSN={["2073-4441"]}, url={https://doi.org/10.3390/w14050696}, DOI={10.3390/w14050696}, abstractNote={Urban development exposes and compacts the subsoil, resulting in reduced infiltration, which often leads to problems with establishing vegetation, increased erosion, and increased runoff volumes. Compost incorporation into these soils can potentially enhance soil physical properties, vegetation establishment, and pollutant removal. The goal of this field study was to determine the efficacy of compost as a soil improvement measure to reduce runoff volume, improve runoff quality, and increase vegetation establishment on a disturbed sandy clay subsoil representing post-development conditions. Two sources of compost were tested: (1) a certified yard waste product at 10%, 30%, and 50% by volume, and (2) an uncertified yard waste product at 30% by volume, both compared to a tilled, no-compost control. Treatment plots were established at Lake Wheeler Road Field Laboratory in Raleigh, NC, and observed for one year. Tilling alone may have been sufficient to reduce runoff quantity as few differences were found between tilled and compost amended plots. Runoff water quality also did not differ according to compost addition. However, the certified compost increased biomass production proportionally to the amount added and compared to the uncertified compost at the same rate. The improved vegetation establishment with compost is important for long-term erosion control and ecosystem services. The results of this study suggest (1) tilling is a viable option to achieve high infiltration rates and reduce runoff volumes, (2) compost incorporation does not reduce nor improve water quality, and (3) compost may yield more robust vegetation establishment.}, number={5}, journal={WATER}, author={Kranz, Christina N. and McLaughlin, Richard A. and Heitman, Joshua L.}, year={2022}, month={Mar} }
 @article{saltiel_heitman_amoozegar_2022, title={Comparison of infiltration test methods for soil health assessment}, volume={77}, ISSN={["1941-3300"]}, DOI={10.2489/jSWC.2022.00178}, number={6}, journal={JOURNAL OF SOIL AND WATER CONSERVATION}, author={Saltiel, T. M. and Heitman, Joshua L. and Amoozegar, A.}, year={2022}, pages={623–629} }
 @article{amoozegar_heitman_kranz_2022, title={Comparison of soil particle density determined by a gas pycnometer using helium, nitrogen, and air}, volume={11}, ISSN={["1435-0661"]}, url={https://doi.org/10.1002/saj2.20476}, DOI={10.1002/saj2.20476}, abstractNote={Abstract Soil particle density (ρ s ) is often assumed as 2.65 g cm −3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρ s in a gas pycnometer and relate measured ρ s to soil particle size distributions. The ρ s of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N 2 , and dry air. The ρ s of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρ s of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm −3 , respectively. The ρ s determined by air and N 2 had much wider ranges with averages of 2.93 and 2.97 g cm −3 , respectively. There was a near 1:1 relationship between ρ s of all samples determined by air and N 2 with a highly significant ( p < .001) correlation coefficient ( r = .99). The average ratio of ρ s determined by He and water was 1.03, but the correlation coefficient for their relationship was only .416. Although the relationship between ρ s determined by He and either air or N 2 was relatively strong ( r < .61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρ s determined by N 2 or air but a weaker, yet statistically significant ( p < .05) relationship when using He.}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Amoozegar, Aziz and Heitman, Joshua L. and Kranz, Christina N.}, year={2022}, month={Nov} }
 @article{morkoc_aguilos_noormets_minick_ile_dickey_hardesty_kerrigan_heitman_king_2022, title={Environmental and Plant-Derived Controls on the Seasonality and Partitioning of Soil Respiration in an American Sycamore (Platanus occidentalis) Bioenergy Plantation Grown at Different Planting Densities}, volume={13}, ISSN={["1999-4907"]}, DOI={10.3390/f13081286}, abstractNote={Bioenergy is one of the most considered alternatives to fossil fuels. Short-rotation woody crops (SRWCs) as bioenergy sources are capable of alleviating energy constraints and sequestering atmospheric CO2. However, studies investigating soil carbon (C) dynamics at SWRC plantations are scarce. We studied American sycamore (Platanus occidentalis) as a model tree species for SRWC at different planting densities ((1) 0.5 × 2.0 m (10,000 trees·ha−1 or tph), (2) 1.0 × 2.0 m (5000 tph), and (3) 2.0 × 2.0 m (2500 tph)) to examine seasonal variation in total soil respiration (Rtotal), partitioned into heterotrophic (Rh) and autotrophic (Ra) respiration, and we evaluated climatic and biological controls on soil respiration. Rtotal and Rh exhibited larger seasonal variation than Ra (p < 0.05). During the nongrowing seasons, the average Rtotal was 0.60 ± 0.21 g·C·m−2·day−1 in winter and 1.41 ± 0.73 g·C·m−2·day−1 in fall. During the growing season, Rtotal was 2–7 times higher in spring (3.49 ± 1.44 g·C·m−2·day−1) and summer (4.01 ± 1.17 g·C·m−2·day−1) than winter. Average Rtotal was 2.30 ± 0.63 g·C·m−2·day−1 in 2500 tph, 2.43 ± 0.64 g·C·m−2·day−1 in 5000 tph, and 2.41 ± 0.75 g·C·m−2·day−1 in 10,000 tph treatments. Average Rh was 1.72 ± 0.40 g·C·m−2·day−1 in 2500 tph, 1.57 ± 0.39 g·C·m−2·day−1 in 5000 tph, and 1.93 ± 0.64 g·C·m−2·day−1 in 10,000 tph, whereas Ra had the lowest rates, with 0.59 ± 0.53 g·C·m−2·day−1 in 2500 tph, 0.86 ± 0.51 g·C·m−2·d−1 in 5000 tph, and 0.48 ± 0.34 g·C·m−2·day−1 in 10,000 tph treatments. Rh had a greater contribution to Rtotal (63%–80%) compared to Ra (20%–37%). Soil temperature was highly correlated to Rtotal (R2 = 0.92) and Rh (R2 = 0.77), while the correlation to Ra was weak (R2 = 0.21). Rtotal, Rh, and Ra significantly declined with soil water content extremes (e.g., <20% or >50%). Total root biomass in winter (469 ± 127 g·C·m−2) was smaller than in summer (616 ± 161 g·C·m−2), and the relationship of total root biomass to Rtotal, Rh, and Ra was only significant during the growing seasons (R2 = 0.12 to 0.50). The litterfall in 5000 tph (121 ± 16 g DW·m−2) did not differ (p > 0.05) from the 2500 tph (108 ± 16 g DW·m−2) or 10,000 tph (132 ± 16 g DW·m−2) treatments. In no circumstances were Rtotal, Rh, and Ra significantly correlated with litterfall amount across planting densities and seasons (p > 0.05). Overall, our results show that Rtotal in American sycamore SRWC is dominated by the heterotrophic component (Rh), is strongly correlated to soil environmental conditions, and can be minimized by planting at a certain tree density (5000 tph).}, number={8}, journal={FORESTS}, author={Morkoc, Suna and Aguilos, Maricar and Noormets, Asko and Minick, Kevan J. and Ile, Omoyemeh and Dickey, David A. and Hardesty, Deanna and Kerrigan, Maccoy and Heitman, Joshua and King, John}, year={2022}, month={Aug} }
 @article{camacho_gannon_ahmed_mulvaney_heitman_amoozegar_leon_2022, title={Evaluation of imazapic and flumioxazin carryover risk for Carinata (Brassica carinata) establishment}, volume={5}, ISSN={["1550-2759"]}, url={https://doi.org/10.1017/wsc.2022.27}, DOI={10.1017/wsc.2022.27}, abstractNote={Abstract Carinata ( Brassica carinata A. Braun) is a potential crop for biofuel production, but the risk of injury resulting from carryover of soil herbicides used in rotational crops is of concern. The present study evaluated the carryover risk of imazapic and flumioxazin for carinata. Label rates of imazapic (70 g ai ha −1 ) and flumioxazin (107 g ai ha −1 ) were applied 24, 18, 12, 6, and 3 mo before carinata planting (MBP). The same herbicides were applied preemergence right after carinata planting at 1X, 0.5X, 0.25X, 0.125X, 0.063X, and 0X the label rate. When either herbicide was applied earlier than 3 MBP, there was no difference in plant density compared with the nontreated control. Carinata damage was <25% when flumioxazin or imazapic was applied at least 6 MBP in Clayton, NC (sandy loam soil), while in Jackson Springs, NC (coarser-textured soil and higher precipitation), at least 12 MPB were needed to lower plant damage to <25%. Preemergence application of 0.063X each herbicide decreased plant density by 40%, with damage reaching >25%. Quantification of herbicide residues in both soils showed that imazapic moved deeper in the soil profile than flumioxazin. This was more evident in Jackson Springs, where 0.68, 3.52, and 7.77 ng of imazapic g −1 soil were detected (15- to 20-cm depth) when the herbicide was applied at 12, 6 and 3 MBP, respectively, while no flumioxazin residues were detected at the same soil depths and times. When residues were 7.78 and 6.90 ng herbicide g −1 soil in the top 10 cm of soil for imazapic and flumioxazin, respectively, carinata exhibited at least 25% damage. Rotational intervals to avoid imazapic and flumioxazin damage to carinata should be between 6 and 12 MBP depending on soil type and environmental conditions, with longer intervals for the former than the latter.}, journal={WEED SCIENCE}, publisher={Cambridge University Press (CUP)}, author={Camacho, Manuel E. and Gannon, Travis W. and Ahmed, Khalied A. and Mulvaney, Michael J. and Heitman, Joshua L. and Amoozegar, Aziz and Leon, Ramon G.}, year={2022}, month={May} }
 @article{dick_gardner_frene_heitman_sucre_leggett_2022, title={Forest floor manipulation effects on the relationship between aggregate stability and ectomycorrhizal fungi}, volume={505}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2021.119873}, abstractNote={Forest floor and mineral soil manipulations influence the soil biogeochemical properties important for loblolly pine (Pinus taeda L.) tree growth. The impacts of forest floor manipulations on soil aggregate stability and the presence of ectomycorrhizal fungi (EMF), was assessed to elucidate the relationship between EMF abundance and aggregate stability. The study site consists of a 14-year-old loblolly pine plantation managed by Weyerhaeuser Company in the Lower Coastal Plain, approximately 8 miles east of New Bern, North Carolina, USA. The soil samples were collected from the top 7.62 cm of each soil treatment which includes three levels of forest floor retention: removed, control, and doubled and two levels of forest floor mixing with the mineral soil: mixed and unmixed. Ectomycorrhizal fungi abundance was evaluated by ester-linked fatty acid methyl ester analysis and microbial community functionality was assessed by acid-phosphatase activity measurement. Aggregate stability was assessed using the aggregate mean weight diameter approach. Results indicate that the forest floor manipulations had no significant impact on aggregate stability and EMF abundance. However, a positive relationship between EMF abundance and aggregate stability was identified. Removing the forest floor resulted in a soil bulk density increase of 0.18 g cm−3 compared to doubling the forest floor. Our results demonstrate that some mineral soil properties recover relatively quickly from forest floor manipulations. The study informs forest managers interested in how soil responds to forest floor manipulation and the interaction between EMF and aggregate stability.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Dick, David L. and Gardner, Terrence G. and Frene, Juan P. and Heitman, Joshua L. and Sucre, Eric B. and Leggett, Zakiya H.}, year={2022}, month={Feb} }
 @article{shehata_heitman_sayde_2022, title={High-Resolution Field Measurement of Soil Heat Capacity and Changes in Soil Moisture Using a Dual-Probe Heat-Pulse Distributed Temperature Sensing Approach}, volume={58}, ISSN={["1944-7973"]}, DOI={10.1029/2021WR031680}, abstractNote={Abstract Increasing interest in studying the variability of soil water content and its spatial scale dependency necessitates the development of new techniques to accurately monitor soil water over a wide range of spatial scales. Distributed Temperature Sensing (DTS) techniques offer unprecedented opportunities to measure temperature with a spatial resolution of a few centimeters over several kilometers, which can be used to measure soil moisture. This study is the first of its kind that investigates under field conditions the feasibility of combining the Dual‐Probe Heat‐Pulse (DPHP) technique with the DTS technology to measure soil thermal properties and variation in soil moisture. A field experiment was conducted over a 30 m transect in the Lake Wheeler Field laboratory in Raleigh, NC. Three different DPHP sensors were constructed from combinations of different fiber optic cables and heating elements and were tested to assess their performance and the effect of their construction characteristics on their accuracy. Measurements were taken over different soil moisture conditions and the system performance was compared against independent soil water content sensors. The system was able to track changes in soil water content with a mean RMSE of 0.02 m 3 m −3 using the optimal DPHP sensor. The key advantage of the tested system is that it does not need any site‐specific calibrations typically required for other DTS‐based systems. The findings of this study provide some practical information and measures that need to be taken for successful DTS‐DPHP construction and application under field conditions.}, number={6}, journal={WATER RESOURCES RESEARCH}, author={Shehata, Mahmoud and Heitman, Joshua and Sayde, Chadi}, year={2022}, month={Jun} }
 @article{kranz_rivers_mclaughlin_heitman_2022, title={Influence of compost application rate on nutrient and heavy metal mobility: Implications for stormwater management}, volume={9}, ISSN={["1537-2537"]}, url={https://doi.org/10.1002/jeq2.20403}, DOI={10.1002/jeq2.20403}, abstractNote={Abstract Amending soils with compost has become increasingly common in stormwater management practices. Compost can be a source and sink for nutrients and heavy metals, and it is important to understand the effect of compost on pollutant leaching under different hydrologic conditions. The objectives of this study were (a) to quantify the distribution coefficient ( K d ) of PO 4 –P and metals (Cd, Cr, Cu, Ni, Pb, Zn) for compost–soil blends and (b) to examine how compost rate alters leaching patterns of nutrients (NH 4 –N, NO 3 –N, PO 4 –P) and metals from compost–soil blends. Material consisted of a sandy loam subsoil, a yard‐waste compost, and compost–soil blends at 20 or 50% compost by volume. Materials were tested in sorption–desorption experiments using simulated stormwater (SW); columns with the materials were also leached with either SW or deionized (DI) water. As compost rate increased, the K d decreased for PO 4 –P and Cr but increased for Cd, Cu, Ni, and Zn. The addition of compost reduced the sorption of PO 4 –P and Cr, potentially making it a source of these pollutants. Simulated stormwater did not increase the amount of pollutants retained compared with DI water for compost blends, except for 100% compost columns. Nitrate was the only constituent that had a negative removal efficiency, suggesting the compost was a source of NO 3 –N. Column media retained >70% of the metals from the added stormwater solution. These results suggest that yard‐waste compost blends at ≤50% have the potential to retain certain pollutants from infiltrating stormwater, but this effect may decline after several storm events.}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Kranz, Christina N. and Rivers, Erin N. and McLaughlin, Richard A. and Heitman, Joshua L.}, year={2022}, month={Sep} }
 @article{sun_xiao_kidron_heitman_2022, title={Insights about biocrust effects on soil gas transport and aeration in drylands: Permeability, diffusivity, and their connection to hydraulic conductivity}, volume={427}, ISSN={["1872-6259"]}, DOI={10.1016/j.geoderma.2022.116137}, abstractNote={Soil gas transport properties and aeration are essential influencing factors of soil chemical and biochemical reactions, especially the respiration processes of plant roots and microorganisms. As ecosystem engineers in drylands, biocrusts may greatly alter surface soil gas transport properties and aeration, but their influences remain unclear and understudied. In a semiarid dryland ecosystem on the Chinese Loess Plateau, the air permeability of bare soil and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) were measured in-situ with naturally changing soil water content. Undisturbed soil samples were also taken for each treatment, and their air permeability and relative gas diffusivity at air-dried and near-saturated conditions, as well as saturated hydraulic conductivity, were determined in the laboratory. We further analyzed the relationship between saturated hydraulic conductivity and air permeability or relative gas diffusivity and calculated the gas and permeability continuity (specific air permeability and specific gas diffusivity) and tortuosity indexes at air-dry and near-saturation. Our results showed that biocrusts were associated with a significantly higher air permeability in contrast to bare soil, and the in situ mean air permeability ranked in order of moss crusts > mixed crusts > cyanobacterial crusts > bare soil. At air-dried condition, biocrusts increased surface soil air permeability by 26% and relative gas diffusivity by 46% as compared with bare soil through decreased surface soil bulk density. In contrast, at near saturation biocrusts decreased air permeability and relative gas diffusivity by 33% and 20%, respectively, which was attributed to pore-clogging by extracellular polymeric substances of biocrusts (3.37 vs. 2.27 mg g−1). Accordingly, at air-dried condition biocrusts increased specific air permeability by 11% and specific gas diffusivity by 30% but decreased tortuosity by 7%. In contrast, they decreased specific air permeability by 76% and specific gas diffusivity by 39% but increased tortuosity by 28% at near-saturated condition. Additionally, the saturated hydraulic conductivity of cyanobacterial, cyanobacterial-moss mixed, and moss crusts were respectively 77%, 69%, and 61% lower than that of bare soil. We found that the relationship between saturated hydraulic conductivity and air permeability or relative gas diffusivity of biocrusts at air-dried condition can be well fitted with a positive linear log–log model (R2 > 0.95). In general, the improved gas transport properties of surface soil caused by different types of biocrusts leads to better soil aeration, which in turn would facilitate microbial activity, soil respiration, and root growth; and impact surface soil water vapor movement induced by evaporation or condensation processes in drylands. Therefore, biocrusts should be carefully considered in further assessments of global dryland hydrology and carbon or nitrogen cycling under changing climate.}, journal={GEODERMA}, author={Sun, Fuhai and Xiao, Bo and Kidron, Giora J. and Heitman, Joshua L.}, year={2022}, month={Dec} }
 @article{bloszies_reberg-horton_heitman_woodley_grossman_hu_2022, title={Legume cover crop type and termination method effects on labile soil carbon and nitrogen and aggregation}, volume={4}, ISSN={["1435-0645"]}, url={https://doi.org/10.1002/agj2.21022}, DOI={10.1002/agj2.21022}, abstractNote={Abstract Growers use cover crops to provide nutrients for crops and build soil organic matter (SOM). Termination methods may alter the effects of cover crops on soil labile C and N. We examined how two cover crops and three termination methods affected soil microbes, soil aggregates, and C and N pools in an organic grain system. We compared crimson clover ( Trifolium incarnatum L.) (CC), hairy vetch ( Vicia villosa Roth) (HV), and a control together with disking, mowing, or a roller‐crimper for effects on hot‐water‐extractable carbohydrates, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), potentially mineralizable C and N, and aggregation (quantified by mean weight diameter [MWD]). Disking comprised flail mowing plots and then cultivating. Roller‐crimping occurred via a roller with blades. Vetch soil contained 14% higher MBC than no cover crop pretermination, possibly because of enhanced rhizodeposition. Planting CC resulted in 44% higher MBC than no cover crop a week after termination, likely due to its higher biomass C/N ratio. Disking decreased MWD relative to flail mowing in no cover crop soils at 4 wk after termination across both years at 0‐to‐5‐cm depth. In addition, MWD was lower under CC than under no cover crop for both the flail mowed and roller‐crimped treatments at 4 wk after termination across both years from 0 to 5 cm. This is possibly due to enhanced desiccation of the soil in bare plots after termination. Our results indicate that quantity and quality of biomass of different legume species, rather than termination methods, dominated effects on labile C.}, number={3}, journal={AGRONOMY JOURNAL}, publisher={Wiley}, author={Bloszies, Sean A. and Reberg-Horton, S. Chris and Heitman, Joshua L. and Woodley, Alex L. and Grossman, Julie M. and Hu, Shuijin}, year={2022}, month={Apr} }
 @article{havlin_austin_hardy_howard_heitman_2022, title={Nutrient Management Effects on Wine Grape Tissue Nutrient Content}, volume={11}, ISSN={["2223-7747"]}, url={https://doi.org/10.3390/plants11020158}, DOI={10.3390/plants11020158}, abstractNote={With limited research supporting local nutrient management decisions in North Carolina grape (Vitis vinifera) production, field studies (2015-17) were conducted to evaluate late season foliar nitrogen (N) application on leaf and petiole N concentration and yeast assimilable N (YAN) in the fruit. Foliar urea (1% v/v) was applied at different rates and application times beginning pre-and post-veraison. Compared to soil applied N, late season foliar N substantially enhanced petiole N and grape YAN. Smaller split N applications were generally more effective in increasing YAN than single larger N rates. These data demonstrate the value of assessing plant N content at full bloom with petiole N analysis or remote sensing to guide foliar N management decisions. Additional field studies (2008-11) were conducted to evaluate pre-bud soil applied phosphorus (P) and potassium (K) effects on petiole P and K nutrient status. Fertilizer P and K were initially broadcast applied (0-896 kg P2O5 ha-1; 0-672 kg K2O ha-1) prior to bud-break in 2008-09 and petiole P and K at full bloom soil test P and K were monitored for three to four years after application. Soil test and petiole P and K were significantly increased with increasing P and K rates, which subsequently declined to near unfertilized levels over the sampling time depending on site and P and K rate applied. These data demonstrate the value of annually monitoring petiole P and K levels to accurately assess plant P and K status to better inform nutrient management decisions.}, number={2}, journal={PLANTS-BASEL}, author={Havlin, John L. and Austin, Robert and Hardy, David and Howard, Adam and Heitman, Josh L.}, year={2022}, month={Jan} }
 @article{xia_zheng_heitman_shi_2022, title={Soil pore size distribution shaped not only compositions but also networks of the soil microbial community}, volume={170}, ISSN={["1873-0272"]}, DOI={10.1016/j.apsoil.2021.104273}, abstractNote={Soil pore size and arrangement control the heterogeneous distribution of nutrients, water, and air and, therefore, are likely a superimposed and integrated factor dictating the soil microbial community structure. It is known that soil with more large pores can potentially harbor more diverse microbes under low hydraulic connectivity. Still, there is scant information on how soil pore size distribution (PSD) governs the composition and association of the microbial community. This work examined PSD effects on microbial community compositions and networks via marker gene high-throughput sequencing of both DNA and cDNA. Three soils with a large variation in silt content (~11–73%) and their combinations at different mass ratios were used to enhance the continuity in silt content and thus PSD. Investigations were made under different levels of total pore volume and pore hydraulic connectivity by incubating soils at varied bulk densities and moisture contents for 50 days. The total of six soils was dichotomized into two PSD groups based on soil water retention curves, with PSD-1 of more macro- and mesopores (>30 μm) and PSD-2 of more micropores (<30 μm). Effects of moisture treatments on both fungal and bacterial evenness and Shannon diversity index were pore size group specific, supporting the importance of pore hydraulic connectivity in regulating microbial diversity. PSD-1 soils promoted the proliferation of Betaproteobacteria, Bacteroidetes, and Eurotiales, whereas PSD-2 soils favored Alphaproteobacteria, Sordariomycetes, and Chaetothyriales. Pore hydraulic connectivity slightly and yet significantly affected the microbial relative abundance of PSD-2 soils, with Actinobacteria being more abundant under drier conditions. There were less intra- and interkingdom associations in PSD-2 than PSD-1 soils, and such differences were little affected by pore volume and pore hydraulic connectivity. Our work highlighted PSD-dependent soil microbial distributions and associations, but ecological consequences need to be further examined.}, journal={APPLIED SOIL ECOLOGY}, author={Xia, Qing and Zheng, Ningguo and Heitman, Joshua L. and Shi, Wei}, year={2022}, month={Feb} }
 @article{fu_horton_ren_heitman_2021, title={A general form of Archie's model for estimating bulk soil electrical conductivity}, volume={597}, ISSN={["1879-2707"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85102588939&partnerID=MN8TOARS}, DOI={10.1016/j.jhydrol.2021.126160}, abstractNote={Electrical conductivity can be used as a surrogate to study the spatial and temporal variabilities of a number of soil properties, e.g., porosity, salinity, clay content and soil moisture. In this study, we develop a general form of Archie’s model that describes the relationship between soil electrical conductivity (σ) and volumetric water content (θ). The input parameters include θ, σ values at dry and saturated conditions (σdry and σsat), soil porosity (ϕ) and sand, silt and clay contents. A value of 2 was given to the water phase exponent (w) based on model calibration with σ and θ datasets obtained from 15 soils. The general form of Archie’s model was evaluated by comparing soil σ estimates to measured σ values from an additional 6 soils. The new model performed well by providing estimates with root mean square errors in the range of 0.008–0.399 dS m−1 and relative errors ranging from 0.7% to 29.8%. The new model is simple, easy to use and ready for further evaluation on a wide range of soil conditions.}, journal={JOURNAL OF HYDROLOGY}, author={Fu, Yongwei and Horton, Robert and Ren, Tusheng and Heitman, J. L.}, year={2021}, month={Jun} }
 @article{crozier_carvalho_johnson_chinn_heitman_2021, title={Appropriate "marginal" farmlands for second-generation biofuel crops in North Carolina}, volume={6}, ISSN={["2471-9625"]}, DOI={10.1002/ael2.20041}, abstractNote={Abstract Current research on bioenergy crops shows that perennial grasses can yield substantial amounts of dry biomass with relatively low inputs of water and fertilizer. In order to minimize competition with food production, it has been suggested that bioenergy crops could be directed to land areas less suitable for commodity crops, commonly referred to as “marginal” lands. These are land units with inherent limitations to vegetative growth and production, which may be due to several factors (soil physical and chemical properties, climatic conditions, etc.). However the term “marginal” is an adjective with imprecise meaning, and objective criteria for determining “marginal” lands for siting bioenergy crops are necessary. Here we propose that such criteria may be based on soil survey classifications and realistic yield estimates, and we show an example of its use to justify site selection for bioenergy crops in different regions of North Carolina.}, number={1}, journal={AGRICULTURAL & ENVIRONMENTAL LETTERS}, author={Crozier, C. R. and Carvalho, H. D. R. and Johnson, A. and Chinn, M. and Heitman, J. L.}, year={2021} }
 @article{lewis_amoozegar_mclaughlin_heitman_2021, title={Comparison of Cornell sprinkle infiltrometer and double-ring infiltrometer methods for measuring steady infiltration rate}, volume={9}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20322}, abstractNote={Abstract Infiltration rate measurements are used to assess soil health and develop land management practices to address runoff from precipitation and irrigation. Differences in observed infiltration rates determined by available methods can be attributed to both the technique and soil property differences. The primary objective of this study was to compare two methods for measuring steady infiltration rate: the Cornell sprinkle infiltrometer (single‐ring) method (CSI), and the double‐ring infiltrometer method (DRI). Measurements were made at four sites using four replications of 13 sets of conditions (52 total paired measurements). The relationship between CSI and DRI measurements was significant ( p < .001) and strong ( R 2 = .71). For 8 of 13 conditions, there was no difference between CSI and DRI steady infiltration rates. Variability in measurements was high (CVs ranged from 0.04 to 1.18) but similar for both methods. Both CSI and DRI results were strongly related to saturated hydraulic conductivity of the surface soil layer determined using a laboratory constant head method on intact soil cores. Overall, results suggest that estimates of steady infiltration rate determined by the CSI and standard DRI methods are comparable.}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Lewis, John and Amoozegar, Aziz and McLaughlin, Richard A. and Heitman, Joshua L.}, year={2021}, month={Sep} }
 @article{fu_lu_ren_horton_heitman_2021, title={Estimating soil water retention curves from soil thermal conductivity measurements}, volume={603}, ISSN={["1879-2707"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85119952884&partnerID=MN8TOARS}, DOI={10.1016/j.jhydrol.2021.127171}, abstractNote={The soil water retention curve represents the relationship between soil water content (θ) and matric potential (ψ). The van Genuchten (vG) model is commonly used to characterize the shape of a θ(ψ) curve. Based on the similarities between θ(ψ) curves and soil thermal conductivity (λ) versus θ curves, Lu and Dong proposed a unified conceptual λ(θ) model (LD model) for estimating λ(θ) curves from θ(ψ) curves. Their work makes it possible to relate the shapes of λ(θ) curves to θ(ψ) curves. In this study, we present an empirical approach to estimate the vG model parameter m from the LD model shape parameter p based on a model calibration with θ(ψ) and λ(θ) datasets obtained from 10 soils. The saturated water content θs and the vG model parameter α are estimated from selected soil properties (i.e., bulk density, particle density, particle size distribution and organic carbon content), and the residual water content θr is estimated from the LD model parameter θf. For model evaluation, the θ(ψ) curves of six soils were estimated from measured λ(θ) values and selected soil properties, and were compared to direct θ(ψ) measurements. The proposed method performed well with root mean square errors of estimated θ values ranging from 0.015 to 0.052 cm3 cm−3 and bias ranging from −0.009 to 0.040 cm3 cm−3. We conclude that the proposed method accurately estimates θ(ψ) curves from λ(θ) curves and selected soil properties.}, journal={JOURNAL OF HYDROLOGY}, author={Fu, Yongwei and Lu, Sen and Ren, Tusheng and Horton, Robert and Heitman, J. L.}, year={2021}, month={Dec} }
 @article{fu_horton_heitman_2021, title={Estimation of soil water retention curves from soil bulk electrical conductivity and water content measurements}, volume={209}, ISSN={["1879-3444"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85100632832&partnerID=MN8TOARS}, DOI={10.1016/j.still.2021.104948}, abstractNote={Measurement of soil water retention curves (SWRCs) is time consuming, and there is no single laboratory device available to measure a SWRC over an entire range of relevant pressures. The van Genuchten (vG) model is commonly used to characterize the shape of the SWRC. Bulk soil electrical conductivity as a function of water content, σ(θ), has been used to estimate hydraulic properties of unsaturated soils, thus making it possible to relate σ(θ) and SWRC. The saturated and residual water content values, θs and θr, can be estimated from soil bulk density and particle size distribution. In this study, we present an approach to estimate vG parameters m and α from σ measured at saturated and residual soil water contents, as well as σ(θ) values measured at intermediate water contents. A thermo-time domain reflectometry (thermo-TDR) sensor is used to measure σ and θ of the same soil sample volume. SWRCs for three soils (Glassil 530 sand, Tennessee silt loam and Illinois clay loam with bulk densities ranging from 1.52 to 1.67 g cm−3, 1.05 to 1.25 g cm−3 and 1.05 to 1.2 g cm−3, respectively) are estimated from σ(θ) measurements and compared with direct SWRC measurements obtained with a tension table and pressure plate extractors. Additional comparisons are made using data obtained from the literature. The proposed method to estimate SWRCs performs well when compared to direct SWRC measurements (with an average RMSE and an average bias of 0.041 cm3 cm−3 and 0.008 cm3 cm−3, respectively). Results indicate that the new σ(θ) based method accurately estimates SWRCs.}, journal={SOIL & TILLAGE RESEARCH}, author={Fu, Yongwei and Horton, Robert and Heitman, Josh}, year={2021}, month={May} }
 @article{schulker_jackson_fonteno_heitman_albano_2021, title={Exploring Substrate Water Capture in Common Greenhouse Substrates through Preconditioning and Irrigation Pulsing Techniques}, volume={11}, ISSN={["2073-4395"]}, DOI={10.3390/agronomy11071355}, abstractNote={Particles in a substrate create a network of pore pathways for water to move through, with size and shape determining the efficacy of these channels. Reduced particle size diversity can lead to increased leachate, poor substrate hydration, and an inefficient irrigation practice. This research examined the hydration characteristics of three greenhouse substrate components at three preconditioned initial moisture contents using subirrigation under five different irrigation durations and three water depths (2 mm, 20 mm, and 35 mm). Sphagnum peatmoss, coconut coir, and aged pine bark were tested at 67%, 50%, and 33% initial moisture (by weight). The objectives were to determine the impact of varying irrigation event durations (5, 10, 20, 30, 60 min) over a 60-min period, and the further influence of water depth and initial moisture, on the water capture abilities of peat, coir, and pine bark. The number of irrigation events depended on the irrigation event time of that experimental unit divided by the total time of 60 min, varying from 12, 6, 3, 2, and 1 event. Hydration efficiency was influenced by initial moisture content (IMC), water depth, pulsing duration, and inherent substrate characteristics (hydrophobicity/hydrophilicity). Initial MC had the largest impact on peat, regardless of water level or irrigation duration. Lower IMCs increased the hydrophobic response of peat, further reducing the amount of water the substrate was able to absorb. Pine bark had a 5–10% decrease in initial hydration between 67%, 50%, and 33% IMC, while coir’s hydrophilic nature reduced any IMC affects. At 50% IMC or less, coir had the highest volumetric water content (VWC) across all substrates, pulsing durations, and water depths. Water depth was found to increase initial hydration and final hydration 6–8% across all substrates. These three materials had altered and varied water capture responses depending on the combination of treatments employed. This work demonstrated the effects of intensity and exposure on substrates and the need for more integrated research for improving water use efficiency on container crops.}, number={7}, journal={AGRONOMY-BASEL}, author={Schulker, Brian A. and Jackson, Brian E. and Fonteno, William C. and Heitman, Joshua L. and Albano, Joseph P.}, year={2021}, month={Jul} }
 @article{morris_vann_heitman_collins_heiniger_2021, title={Maximizing soybean yield by understanding planting date, maturity group, and seeding rate interactions in North Carolina}, volume={9}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.20603}, abstractNote={Growers across theU.S. Southeast use a diversity of soybean [Glycine max (L.) Merr.] planting dates, maturity groups, and seeding rates for soybean production depending on their rotational complexity. Studies were conducted across seven North Carolina environments in 2019 and 2020 to determine the effect of planting date (mid-March through mid-July), maturity group (MG 2–8), and seeding rate (185,329–432,434 seeds ha–1) on soybean emergence, stand, and yield. Across environments, soybean typically emerged more quickly with later planting dates; however, there were location-specific variations in soybean emergence due to weather conditions around the time of planting. The longest and shortest emergence periods were 26 d for soybean planted in mid-March and 4 d for soybean planted in June and July, respectively. In the higher yielding environments, yield was maximized with MG 3–4 cultivars planted at early April planting dates and yield declined as planting was delayed. In the low yield environments, yield was maximized with late April to mid-May planting dates, typically with MG 5–7 cultivars. There was a penalty in both yield environments to planting past mid-May and in the low yield environments for planting before mid-April. Across environments, yields tended to be more similar among cultivars higher than MG 3 at planting dates in June and July. The effect of seeding rate on soybean yield was variable across planting dates, maturity groups, and yield environments. Future research is needed in North Carolina to validate the planting date and maturity group interactions on yield observed in this experiment to capture more variation in weather conditions.}, journal={CROP SCIENCE}, author={Morris, Tristan C. and Vann, Rachel A. and Heitman, Josh and Collins, Guy D. and Heiniger, Ryan W.}, year={2021}, month={Sep} }
 @article{tian_chen_cai_gao_ren_heitman_horton_2021, title={New pedotransfer functions for soil water retention curves that better account for bulk density effects}, volume={205}, ISSN={["1879-3444"]}, DOI={10.1016/j.still.2020.104812}, abstractNote={Abstract Pedotransfer functions (PTFs) describing soil water retention curves (WRCs) have been widely used in crop, soil, and land surface models. A limitation of the available PTFs is that they fail to account for shape changes in WRCs due to bulk density variations caused by soil tillage, compaction, and other processes. This study develops new PTFs that include bulk density effects on the WRC shape. A new framework is introduced to build the bulk density-associated PTFs based on a widely-used WRC dataset. The new PTFs were validated by comparing the performance with two common PTFs from the literature using two independent datasets. The results show that the newly developed PTFs provide reliable WRC estimates for the validation datasets, with mean RMSE values of 0.055 and 0.059 m3 m-3, respectively. The accuracy of the new PTFs is comparable or in some cases better than the common PTFs. While the literature PTFs investigated do not always properly describe bulk density effects on WRC changes, the new PTFs effectively account for such effects on the WRC shape, thus have the potential to be integrated into crop and soil management models to represent bulk density impacts on WRCs due to anthropogenic (e.g., plowing and compaction) and natural (e.g., wetting/drying) processes.}, journal={SOIL & TILLAGE RESEARCH}, author={Tian, Zhengchao and Chen, Jiazhou and Cai, Chongfa and Gao, Weida and Ren, Tusheng and Heitman, Joshua L. and Horton, Robert}, year={2021}, month={Jan} }
 @article{morris_vann_collins_heitman_kulesza_2021, title={Planting date and maturity group impact on soybean seed quality in the southeastern United States}, volume={11}, ISSN={["1435-0645"]}, DOI={10.1002/agj2.20913}, abstractNote={Abstract The impacts on soybean seed quality from shifting to using earlier soybean planting dates (PDs) and earlier‐maturing varieties in the southeastern United States are not well understood. The objective of this study was to determine the impact of diverse PDs and maturity groups (MGs) on soybean protein content, oil content, seed damage, and purple seed stain. Studies were installed across seven North Carolina locations in 2019 and 2020 to determine the impact of PD (mid‐March through mid‐July) and MG (2–7) on seed quality. Protein content declined as planting was delayed for the early MGs (2–5) but was stable across PD for the later MGs (6–7). It was observed that early‐maturing varieties (MG ≤5) had a lower protein content than the later‐maturing varieties (MGs 6–7). The oil content was greater in the early MGs (MGs 2–4) compared with the later MGs (MGs 5–7), with oil content and protein content having an inverse relationship. Seed damage was greatest when planting before late April with early MGs (MGs 2–4). Less purple seed stain was found in MGs 5–7 compared with the earlier MGs across all PDs. Further research is needed to understand how to minimize seed damage and purple seed stain as producers consider shifting to an earlier production system for the associated yield benefits in North Carolina and across the southeastern United States.}, journal={AGRONOMY JOURNAL}, author={Morris, Tristan C. and Vann, Rachel A. and Collins, Guy D. and Heitman, Joshua and Kulesza, Stephanie B.}, year={2021}, month={Nov} }
 @article{rivers_heitman_mclaughlin_howard_2021, title={Reducing roadside runoff: Tillage and compost improve stormwater mitigation in urban soils}, volume={280}, ISSN={["1095-8630"]}, DOI={10.1016/j.jenvman.2020.111732}, abstractNote={Soils adjacent to urban surfaces are often impaired by construction activities that degrade the natural structure and function of the soil, resulting in altered physical, hydraulic, and vegetative properties that limit the infiltration, storage, and filtration of stormwater runoff. A management approach to enhance the efficacy of vegetated roadside soils for runoff control is the use of compost in conjunction with tillage to improve soil conditions and facilitate improved hydrological function, the establishment of vegetative biomass, and increased nutrient and pollutant attenuation. The purpose of this study was to determine the efficacy of soil improvement measures to reduce runoff volumes and improve water quality along roadsides over time. The effects of tillage with and without compost on 1) bulk density and infiltration rates, 2) runoff volumes, and 3) runoff water quality were evaluated during multiple storm events along two long-established interstate roadsides in North Carolina during 2015 and 2017. Experimental plots were established in the grassed areas adjacent to roads and consisted of an untreated control, tillage only, and tillage amended with compost. Tillage alone did not reduce runoff in roadside soils, however, tillage with compost did improve runoff capture. The patterns in hydrologic performance within and among sites suggests that the incorporation of compost in tilled soils may influence storage potential through different effects on soil properties, such as decreasing bulk density or improving vegetation establishment, thereby increasing evapotranspirative withdrawals, depending on soil texture. Tillage increased sediment concentrations in runoff, however, net export of sediments was reduced with the inclusion of compost due to the reduction of runoff quantities compared to undisturbed areas and tillage alone. Control and treatment plots were equally effective in reducing dissolved nutrient and metal concentrations, however, the improved hydrologic performance in plots with compost decreased net nutrient and metal export in most storms. The results of this study suggest that the incorporation of compost in compacted urban soils may provide significant improvements for biological and physical soil properties that affect stormwater interception and infiltration.}, number={111732}, journal={JOURNAL OF ENVIRONMENTAL MANAGEMENT}, author={Rivers, Erin N. and Heitman, Joshua L. and McLaughlin, Richard A. and Howard, Adam M.}, year={2021}, month={Feb} }
 @article{ile_aguilos_morkoc_heitman_king_2021, title={Root Biomass Distribution and Soil Physical Properties of Short-Rotation Coppice American Sycamore (Platanus occidentalis L.) Grown at Different Planting Densities}, volume={12}, ISSN={["1999-4907"]}, DOI={10.3390/f12121806}, abstractNote={Short rotation woody crops (SRWCs) provide sustainable, renewable biomass energy and offer potential ecosystem services, including increased carbon storage, reduced greenhouse gas emissions, and improved soil health. Establishing SRWCs on degraded lands has potential to enhance soil properties through root and organic matter turnover. A better understanding of SRWC planting density and its associated root turnover impacts on soil–air–water relations can improve management. In this study, we investigate the effects of planting density for a low-input American sycamore SRWC (no fertilization/irrigation) on soil physical properties for a degraded agricultural site in the North Carolina piedmont. The objectives were (1) to estimate the distributions of coarse and fine root biomass in three planting densities (10,000, 5000, and 2500 trees per hectare (tph)) and (2) to assess the effects of planting density on soil hydraulic properties and pore size distribution. Our results show that planting at 10,000 tph produced significantly higher amounts of fine root biomass than at lower planting densities (p < 0.01). In the 25,000 tph plots, there was significantly higher amounts of coarse root biomass than for higher planting densities (p < 0.05). The 10,000 tph plots had lower plant available water capacity but larger drainable porosity and saturated hydraulic conductivity compared with lower planting densities (<0.05). The 10,000 tph plots total porosity was more dominated by larger pore size fractions compared with the 5000 and 2500 tph. Generally, our findings show similar patterns of soil hydraulic properties and pore size distributions for lower planting densities. The results from 10,000 tph indicate a higher air-filled pore space at field capacity and more rapid drainage compared with lower planting densities. Both characteristics observed in the 10,000 tph are favorable for aeration and oxygen uptake, which are especially important at wet sites. Overall, the results suggest that improved soil health can be achieved from the establishment of American sycamore SRCs on marginal lands, thereby providing a green pathway to achieving environmental sustainability with woody renewable energy.}, number={12}, journal={FORESTS}, author={Ile, Omoyemeh Jennifer and Aguilos, Maricar and Morkoc, Suna and Heitman, Joshua and King, John S.}, year={2021}, month={Dec} }
 @article{fu_lu_heitman_ren_2021, title={Root influences on soil bulk density measurements with thermo-time domain reflectometry}, volume={403}, ISSN={["1872-6259"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85105587572&partnerID=MN8TOARS}, DOI={10.1016/j.geoderma.2021.115195}, abstractNote={• Root influences on soil bulk density measurements with thermo-TDR technique are quantified. • The extended de Vires heat capacity model is used to account for the root effects. • A critical root density that affects thermo-TDR measurements is determined. The thermo-TDR (time domain reflectometry) technique has been applied for measuring soil bulk density (ρ b ) in-situ. However, the accuracy of thermo-TDR measured ρ b data, as influenced by plant roots, has not been studied. In this study, we applied the extended de Vries heat capacity model to examine the influences of roots on thermo-TDR sensor performance for measuring ρ b dynamics in the root zone. Soil samples were collected at multiple depths and horizontal positions over time during a maize growth period, and ρ b values were determined gravimetrically and indirectly from thermo-TDR measurements. Results showed that by using the extended de Vries model, the thermo-TDR measured ρ b agreed well with the gravimetric values. Ignoring root contribution to bulk soil heat capacity introduced 6.7%, 13.8% and 13.9% errors in thermo-TDR measured ρ b data on the loamy sand, sandy loam, and clay loam soils, respectively. A critical root density of 0.037 g cm −3 was determined beyond which roots may induce ρ b errors greater than 0.1 g cm −3 with the thermo-TDR technique.}, journal={GEODERMA}, author={Fu, Yongwei and Lu, Yili and Heitman, Joshua and Ren, Tusheng}, year={2021}, month={Dec} }
 @article{camacho_heitman_gannon_amoozegar_leon_2021, title={Seed germination responses to soil hydraulic conductivity and polyethylene glycol (PEG) osmotic solutions}, volume={462}, ISSN={["1573-5036"]}, url={https://doi.org/10.1007/s11104-021-04857-5}, DOI={10.1007/s11104-021-04857-5}, number={1-2}, journal={PLANT AND SOIL}, author={Camacho, Manuel E. and Heitman, Joshua L. and Gannon, Travis W. and Amoozegar, Aziz and Leon, Ramon G.}, year={2021}, month={May}, pages={175–188} }
 @article{kool_tong_tian_heitman_sauer_horton_2021, title={Soil water retention and hydraulic conductivity dynamics following tillage (vol 193, pg 95, 2019)}, volume={207}, ISSN={["1879-3444"]}, DOI={10.1016/j.still.2020.104853}, journal={SOIL & TILLAGE RESEARCH}, author={Kool, D. and Tong, B. and Tian, Z. and Heitman, J. L. and Sauer, T. J. and Horton, R.}, year={2021}, month={Mar} }
 @article{stephenson_carvalho_castillo_crozier_smyth_heitman_2021, title={Water use and biomass yield of bioenergy crops in the North Carolina Piedmont}, volume={113}, ISSN={["1435-0645"]}, DOI={10.1002/agj2.20646}, number={3}, journal={AGRONOMY JOURNAL}, author={Stephenson, Thomas D. and Carvalho, Henrique D. R. and Castillo, Miguel S. and Crozier, Carl R. and Smyth, Thomas J. and Heitman, Joshua L.}, year={2021}, month={May}, pages={2463–2473} }
 @article{zhang_ren_heitman_horton_2020, title={Advances in heat-pulse methods: Measuring near-surface soil water content}, volume={84}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20150}, abstractNote={Abstract Soil water content (θ) influences physical, chemical, and biological processes in the soil. Near‐surface θ (<1‐cm depth) is particularly important for surface energy partitioning, but few techniques are available for near‐surface in situ θ measurements. Heat‐pulse sensors can be used to determine the soil volumetric heat capacity, which is linearly related to θ. Here we describe the principles and procedures of determining near‐surface in situ θ with a heat pulse sensor. The main limitations and potential errors associated with the method are also presented. When ambient soil temperature drift and the soil–air interface effects are addressed, the error in the heat‐pulse‐determined θ is greatly reduced. For an example, data series with θ data determined by gravimetric initial θ and heat‐pulse‐based change in θ (Δθ), results agree well with gravimetric θ values, yielding a coefficient of determination of 0.95. We conclude that heat‐pulse sensors are useful tools for continuously and nondestructively determining near‐surface θ of non‐shrink–swell soils.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Zhang, Xiao and Ren, Tusheng and Heitman, Joshua and Horton, Robert}, year={2020}, pages={1376–1383} }
 @article{heitman_zhang_xiao_ren_horton_2020, title={Advances in heat-pulse methods: Measuring soil water evaporation with sensible heat balance}, volume={84}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20149}, abstractNote={Abstract Soil water evaporation is an important process in hydrology, engineering, and agriculture. Few techniques are capable of measuring soil water evaporation in situ. An approach has been developed to measure in situ subsurface soil water evaporation using a soil sensible heat balance (SHB) with measurement data obtained from multi‐needle heat‐pulse sensors. Terms in the SHB (i.e., sensible heat flux and change in sensible heat storage) are calculated from heat‐pulse sensor derived soil temperature and thermal property (i.e., thermal conductivity and heat capacity) measurements for a thin soil layer with thickness corresponding to the sensor geometry. The quantity of latent heat required for soil water vaporization can be determined as the residual to the SHB (i.e., change in heat flux with depth minus change in sensible heat storage with time) for the soil layer. Dividing latent heat (per unit time) by heat of vaporization for water allows data to be converted to evaporation rate. Numerical analysis indicates that the SHB approach is most sensitive to the heat flux component of the SHB. Laboratory and field tests indicate that SHB results compare favorably with mass‐balance and micrometeorologic approaches for evaporation measurement, with SHB typically differing by <0.2 mm d −1 from the reference methods.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Heitman, J. L. and Zhang, X. and Xiao, X. and Ren, T. and Horton, R.}, year={2020}, pages={1371–1375} }
 @article{tian_kojima_heitman_horton_ren_2020, title={Advances in thermo-time domain reflectometry technique: Measuring ice content in partially frozen soils}, volume={84}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20160}, abstractNote={Abstract Ice content (θ i ) is a critical parameter affecting soil thermal, mechanical, and hydraulic properties in cold regions. Few techniques are available for accurately determining θ i in laboratory samples and in situ. A combined heat‐pulse and time domain reflectometry (thermo‐TDR) sensor, which measures soil thermal properties and electrical properties simultaneously, can be used to estimate θ i . The thermo‐TDR method determines θ i by using a heat‐capacity‐based ( C ‐based) approach or a thermal‐conductivity‐based (λ‐based) approach. Here, we describe the principles and procedures of such approaches. The C ‐based thermo‐TDR approach is simple to use and provides reasonable θ i values at temperatures below −5°C, but it fails at higher temperatures. The λ‐based approach, which solves for θ i from thermo‐TDR measurements with an iterative method, gives more accurate θ i estimates than does the C ‐based approach and extends the thermo‐TDR measurement range to temperatures near the freezing point of water. Therefore, the λ‐based thermo‐TDR method is preferred for determining θ i in partially frozen soils.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Tian, Zhengchao and Kojima, Yuki and Heitman, Joshua L. and Horton, Robert and Ren, Tusheng}, year={2020}, pages={1519–1526} }
 @article{caudle_osmond_heitman_ricker_miller_wills_2020, title={Comparison of Soil Health Metrics for a Cecil Soil in the North Carolina Piedmont}, volume={84}, journal={Soil Science Society  of America Journal}, author={Caudle, C. and Osmond, D. and Heitman, J. and Ricker, M. and Miller, G. and Wills, S.}, year={2020}, pages={978–983} }
 @article{schulker_jackson_fonteno_heitman_albano_2020, title={Comparison of Water Capture Efficiency through Two Irrigation Techniques of Three Common Greenhouse Soilless Substrate Components}, volume={10}, ISSN={["2073-4395"]}, DOI={10.3390/agronomy10091389}, abstractNote={Substrate wettability is an important factor in determining effective and efficient irrigation techniques for container-grown crops. Reduced substrate wettability can lead to lower substrate water capture, excessive leaching and poor plant growth. This research examined substrate water capture using surface and subirrigation under three initial moisture contents (IMC). Sphagnum peat moss, coconut coir, and pine bark were tested at IMCs of 67% 50%, and 33%. Substrate water capture was influenced by both IMC and irrigation technique. Surface irrigation increased the water capture of coir and peat, regardless of IMC, whereas IMC influenced pine bark water capture more than irrigation method. Surface-irrigated coir at or above 50% IMC provided the greatest water capture across all treatments. The first irrigation had the highest capture rate compared to all other events combined. Container capacities of pine bark and coir were unaffected by IMC and irrigation type, but the CC of peat was less by ~ 40% volumetrically under low IMC conditions. Coir, had the greatest ability to capture water, followed by pine bark and peat, respectively. Moisture content, irrigation type and component selection all influence the water capture efficiency of a container substrate.}, number={9}, journal={AGRONOMY-BASEL}, author={Schulker, Brian A. and Jackson, Brian E. and Fonteno, William C. and Heitman, Joshua L. and Albano, Joseph P.}, year={2020}, month={Sep} }
 @article{fields_fonteno_jackson_heitman_owen_2020, title={Comparison of Water Capture Efficiency through Two Irrigation Techniques of Three Common Greenhouse Soilless Substrate Components}, volume={10}, number={1393}, journal={Agronomy}, author={Fields, J.S. and Fonteno, W.C. and Jackson, B.E. and Heitman, J.L. and Owen, J.S.}, year={2020} }
 @article{tian_ren_horton_heitman_2020, title={Estimating soil bulk density with combined commercial soil water content and thermal property sensors}, volume={196}, ISSN={["1879-3444"]}, DOI={10.1016/j.still.2019.104445}, abstractNote={Abstract Accurate information of soil bulk density (ρb) is essential for many models that predict soil water, gas, and heat transfer processes and for estimating soil carbon pools. Several indirect methods have been used to estimate ρb as a derivative of various soil properties. One approach is to estimate ρb from soil thermal conductivity (λ) and volumetric water content (θw) measured with a custom fabricated sensor (thermo-TDR). In this study, we introduce a new approach to determine ρb with a combination of commercially available θw and thermal property sensors. Repacked samples of four differently-textured soils and a field experiment on a clay soil were used to evaluate the ability of four available sensors from METER Group, Inc. (Pullman, WA, USA) to estimate ρb. The θw was measured with the GS3 and EC-5 sensors, and soil λ was determined with the TR-1 and SH-1 thermal property sensors. The θw and λ measurements were used to determine ρb inversely from a λ-model. Compared with the GS3 sensor, the EC-5 sensor provided more accurate measurements of θw for the investigated soils, and thus, the EC-5 sensor was used with the new ρb estimation approach. Both TR-1 and SH-1 sensors gave accurate λ estimates when compared to modeled values. The ρb estimates with the TR-1/EC-5 and SH-1/EC-5 sensor combination methods agreed well with independent gravimetrically-derived ρb values of the repacked samples and the in-situ measurements, with average root mean square errors of 0.12 and 0.13 Mg m−3, respectively. Thus, the commercial multi-sensor combinations can provide accurate ρb estimates similar to those with custom fabricated thermo-TDR sensors, and they are simpler to operate than the custom fabricated sensors.}, journal={SOIL & TILLAGE RESEARCH}, author={Tian, Zhengchao and Ren, Tusheng and Horton, Robert and Heitman, Joshua L.}, year={2020}, month={Feb} }
 @article{tian_ren_heitman_horton_2020, title={Estimating thermal conductivity of frozen soils from air-filled porosity}, volume={84}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20102}, abstractNote={Abstract Soil thermal conductivity (λ) is an important thermal property for environmental, agricultural, and engineering heat transfer applications. Existing λ models for frozen soils are complicated to use because they require estimates of both liquid water content and ice content. This study introduces a new approach to estimate λ of partially frozen soils from air‐filled porosity ( n a ), which can be determined by using an oven‐drying method. A λ and n a relationship was established based on measurements for 28 partially frozen soils. A strong exponential relationship between λ and n a was found (with R 2 of 0.82). Independent tests on 10 partially frozen soils showed that the exponential λ– n a model produced reliable λ estimates with a RMSE of 0.319 W m −1 K −1 , which was smaller than those of two widely used λ models for partially frozen soils. The λ– n a model is easier to use than existing models, because it requires fewer parameters. Note that the λ‐ n a model ignores the effect of temperature on λ of frozen soils and is most applicable to soil at temperatures of at least −4 °C.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Tian, Zhengchao and Ren, Tusheng and Heitman, Joshua L. and Horton, Robert}, year={2020}, pages={1650–1657} }
 @article{shehata_heitman_ishak_sayde_2020, title={High-Resolution Measurement of Soil Thermal Properties and Moisture Content Using a Novel Heated Fiber Optics Approach}, volume={56}, ISSN={["1944-7973"]}, DOI={10.1029/2019WR025204}, abstractNote={Abstract Hydrological parameters are scale dependent. Efficient monitoring techniques capable of measuring hydrological parameters, such as soil moisture content ( θ ), over a wide range of spatial scales are essential for understanding the complexity of water and energy movement across the landscape. Techniques to measure θ over spatial scales in the range from centimeters to thousands of meters, however, are sorely lacking. Recent improvements in the distributed temperature sensing (DTS) technology supported the development of novel techniques to fill that gap. However, improvements in the accuracy and applicability of DTS techniques are still needed. This study investigates the possibility of improving the accuracy of the fiber optics dual‐probe heat‐pulse (FO‐DPHP) DTS technique by using a new design to maintain the spacing between the FO‐DPHP probes and by introducing a novel data interpretation approach. The accuracy of the novel FO‐DPHP design was tested at different θ in a sand column experiment. The FO‐DPHP measurements obtained using traditional and novel data interpretation approaches were compared against independent measurements from several calibrated soil water content (EC5) sensors. Monte‐Carlo analyses were also performed to assess the impact of DTS measurement errors on the accuracy achieved using the data interpretation approaches. The novel design and data interpretation approach allowed for accurate measurements of soil thermal properties and θ without the need to perform a hard‐to‐achieve soil‐specific calibration. Measured θ had mean errors and standard deviations <0.03 and <0.01 m 3 m −3 , respectively, for moisture conditions ranging from dry to near saturation. The standard deviation in the measured heat capacity was <0.01 MJ m −3 K −1 .}, number={7}, journal={WATER RESOURCES RESEARCH}, author={Shehata, Mahmoud and Heitman, Joshua and Ishak, Joseph and Sayde, Chadi}, year={2020}, month={Jul} }
 @article{fields_owen_stewart_heitman_caron_2020, title={Modeling water fluxes through containerized soilless substrates using HYDRUS}, volume={19}, ISSN={["1539-1663"]}, DOI={10.1002/vzj2.20031}, abstractNote={Abstract Containerized crop production can enhance plant health and ensure environmental sustainability, yet proper management requires improved understanding of water fluxes and storage within soilless substrates. Numerical simulation tools developed to simulate water movement in porous media, such as HYDRUS‐3D, may help to quantify effective hydraulic properties of soilless substrates but have not yet been tested in this capacity. Therefore, this study had three main objectives: (a) to assess the accuracy of HYDRUS‐3D for simulating water flow through peat‐ and bark‐based soilless substrates by comparing measured and modeled drainage and water storage; (b) to determine sensitivity of model outputs to individual hydraulic parameters; and (c) to compare model parameterization using three laboratory characterization methods (instantaneous profile sorption, instantaneous profile desorption, and evaporation) vs. inverse modeling with HYDRUS. The results showed that the modeled water contents and drainage timing and amounts were most sensitive to saturated volumetric water content (θ s ) and least sensitive to saturated hydraulic conductivity ( K s ). With regard to parameterization methods, the inverse modeling approach provided the most accurate water balance simulations for both substrates, followed by the sorption method. These two methods estimated lower peak water contents and greater drainage compared with simulations parameterized using desorption and evaporation measurements. Overall, the study results showed that the Richards equation, as calculated using HYDRUS, can provide accurate simulations of water flux through containers when properly calibrated, though sorption‐derived parameters may suffice when model optimization is impractical.}, number={1}, journal={VADOSE ZONE JOURNAL}, author={Fields, Jeb S. and Owen, James S., Jr. and Stewart, Ryan D. and Heitman, Josh L. and Caron, Jean}, year={2020} }
 @article{tian_chen_cai_gao_ren_heitman_horton_2020, title={New Pedotransfer Functions for Soil Water Retention Curves that Better Account for Bulk Density Effects}, volume={205}, number={104812}, journal={Soil and Tillage Research}, author={Tian, Z. and Chen, J. and Cai, C. and Gao, W. and Ren, T. and Heitman, J.L. and Horton, R.}, year={2020} }
 @article{fu_lu_heitman_ren_2020, title={Root-Induced Changes in Soil Thermal and Dielectric Properties Should not be Ignored}, volume={370}, number={114352}, journal={Geoderma}, author={Fu, Y. and Lu, Y. and Heitman, J.L. and Ren, T.}, year={2020} }
 @article{fields_fonteno_jackson_heitman_owen_2020, title={The Use of Dewpoint Hygrometry to Measure Low Water Potentials in Soilless Substrate Components and Composites}, volume={10}, ISSN={["2073-4395"]}, DOI={10.3390/agronomy10091393}, abstractNote={Plant water availability in soilless substrates is an important management consideration to maximize water efficiency for containerized crops. Changes in the characteristics (i.e., shrink) of these substrates at low water potential (<−1.0 MPa) when using a conventional pressure plate-base can reduce hydraulic connectivity between the plate and the substrate sample resulting in inaccurate measures of water retention. Soilless substrate components Sphagnum peatmoss, coconut coir, aged pine bark, shredded pine wood, pine wood chips, and two substrate composites were tested to determine the range of volumetric water content (VWC) of surface-bound water at water potentials between −1.0 to −2.0 MPa. Substrate water potentials were measured utilizing dewpoint hygrometry. The VWC for all components or composites was between 5% and 14%. These results were considerably lower compared to previous research (25% to 35% VWC) utilizing conventional pressure plate extraction techniques. This suggests that pressure plate measurements may overestimate this surface-bound water which is generally considered unavailable for plant uptake. This would result in underestimating available water by as much as 50%.}, number={9}, journal={AGRONOMY-BASEL}, author={Fields, Jeb S. and Fonteno, William C. and Jackson, Brian E. and Heitman, Joshua L. and Owen, James S., Jr.}, year={2020}, month={Sep} }
 @article{kranz_mclaughlin_johnson_miller_heitman_2020, title={The effects of compost incorporation on soil physical properties in urban soils – A concise review}, volume={261}, ISSN={0301-4797}, url={http://dx.doi.org/10.1016/j.jenvman.2020.110209}, DOI={10.1016/j.jenvman.2020.110209}, abstractNote={Incorporation of compost into soil can significantly alter soil physical properties, nutrient dynamics, and vegetation establishment. Strategic compost application to disturbed, degraded urban soil may provide benefits to soil properties. This review compared twenty-five peer-reviewed studies that evaluated changes in soil bulk density, infiltration rate, hydraulic conductivity, and water retention where compost was incorporated into urban soils. A wide range of compost rates and incorporation depths were evaluated in these studies across many soil types. Compost incorporation generally reduced bulk density, enhanced infiltration and hydraulic conductivity, and increased water content and plant available water, compared to unamended controls. In the four studies on runoff water quality, compost incorporation often resulted in higher initial nutrient content in runoff water, but also enhanced grass growth and reduced sediment loss. Few studies evaluated multiple compost application rates or incorporation depths, and the ways in which compost application rates were reported varied widely between studies making it difficult to directly compare them. Four studies investigated the long-term effects of compost incorporation, and there was no clear pattern of why some soils display enhanced physical properties over time and others do not. Compost was largely reported to have a positive effect on degraded urban soils. Little research has focused on the longevity of compost in urban soils after one application, and thus, this would be a valuable topic of further investigation.}, journal={Journal of Environmental Management}, publisher={Elsevier BV}, author={Kranz, Christina N. and McLaughlin, Richard A. and Johnson, Amy and Miller, Grady and Heitman, Joshua L.}, year={2020}, month={May}, pages={110209} }
 @article{tong_kool_heitman_sauer_gao_horton_2020, title={Thermal Property Values of a Central Iowa Soil as Functions of Soil Water Content and Bulk Density or of Soil Air Content}, volume={71}, DOI={https://doi.org/10.1111/ejss.12856}, abstractNote={Abstract Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content ( θ ) and bulk density ( ρ b ). Both θ and ρ b change with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes with θ and ρ b . The objective of this study is to examine how changes in ρ b with time after tillage impact soil thermal properties (volumetric heat capacity, C v , thermal diffusivity, k , and thermal conductivity, λ ). The study provides thermal property values as functions of θ and ρ b and of air content ( n air ) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated ( θ at pressure head of −50 kPa) and oven‐dry conditions. Generally, k and λ increased with increasing ρ b at the three water conditions. The C v increased as ρ b increased in the oven‐dry and unsaturated conditions and decreased as ρ b increased in the saturated condition. For a given θ , a larger ρ b was associated with larger thermal property values, especially for λ . The figures of C v , k and λ versus θ and ρ b , as well as C v , k and λ versus n air , represented the range of soil conditions following tillage. Trends in the relationships of thermal property values with θ and ρ b were described by 3‐D surfaces, whereas each thermal property had a linear relationship with n air . Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varying θ and ρ b . The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions of θ and ρ b or as linear functions of n air . Highlights Thermal property values for a range of θ and ρ b were measured on undisturbed soil cores. Freshly tilled soil thermal property values were quite dynamic temporally. The thermal property values of a tilled soil were described as 3‐D surfaces with θ and ρ b . The thermal property values of a tilled soil varied linearly with n air .}, number={2}, journal={European Journal of Soil Sciences}, author={Tong, B. and Kool, D. and Heitman, J.L. and Sauer, T.J. and Gao, Z. and Horton, R.}, year={2020}, month={Jun}, pages={169–178} }
 @article{tong_kool_heitman_sauer_gao_horton_2020, title={Thermal property values of a central Iowa soil as functions of soil water content and bulk density or of soil air content}, volume={71}, ISSN={["1365-2389"]}, DOI={10.1111/ejss.12856}, abstractNote={Abstract Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content ( θ ) and bulk density ( ρ b ). Both θ and ρ b change with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes with θ and ρ b . The objective of this study is to examine how changes in ρ b with time after tillage impact soil thermal properties (volumetric heat capacity, C v , thermal diffusivity, k , and thermal conductivity, λ ). The study provides thermal property values as functions of θ and ρ b and of air content ( n air ) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated ( θ at pressure head of −50 kPa) and oven‐dry conditions. Generally, k and λ increased with increasing ρ b at the three water conditions. The C v increased as ρ b increased in the oven‐dry and unsaturated conditions and decreased as ρ b increased in the saturated condition. For a given θ , a larger ρ b was associated with larger thermal property values, especially for λ . The figures of C v , k and λ versus θ and ρ b , as well as C v , k and λ versus n air , represented the range of soil conditions following tillage. Trends in the relationships of thermal property values with θ and ρ b were described by 3‐D surfaces, whereas each thermal property had a linear relationship with n air . Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varying θ and ρ b . The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions of θ and ρ b or as linear functions of n air . Highlights Thermal property values for a range of θ and ρ b were measured on undisturbed soil cores. Freshly tilled soil thermal property values were quite dynamic temporally. The thermal property values of a tilled soil were described as 3‐D surfaces with θ and ρ b . The thermal property values of a tilled soil varied linearly with n air .}, number={2}, journal={EUROPEAN JOURNAL OF SOIL SCIENCE}, author={Tong, Bing and Kool, Dilia and Heitman, Joshua L. and Sauer, Thomas J. and Gao, Zhiqiu and Horton, Robert}, year={2020}, month={Mar}, pages={169–178} }
 @article{lu_liu_zhang_heitman_horton_ren_2020, title={Thermo-time domain reflectometry method: Advances in monitoring in situ soil bulk density}, volume={84}, ISSN={["1435-0661"]}, DOI={10.1002/saj2.20147}, abstractNote={Abstract Soil bulk density (ρ b ) is a critical parameter for describing soil structure and physical processes, yet traditional methods are unable to capture spatial and temporal changes in ρ b . Recently the thermo–time domain reflectometry (thermo‐TDR) technique has been applied to determine in situ ρ b on the basis of soil thermal property and water content measurements. Here, we present theory, instrumentation, procedures, and comments for monitoring in situ ρ b with the thermo‐TDR sensor. We conclude that the thermo‐TDR sensor offers a useful tool for determining ρ b continuously and nondestructively.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Lu, Yili and Liu, Xiaona and Zhang, Meng and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2020}, pages={1354–1360} }
 @article{roper_osmond_heitman_2019, title={A Response to "Reanalysis Validates Soil Health Indicator Sensitivity and Correlation with Long-term Crop Yields"}, volume={83}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2019.06.0198}, abstractNote={We published data showing that current soil health indicator (SHI) assessments do not consistently detect differences in a range of soil management practices implemented in North Carolina soils. Van Es and Karlen reanalyzed our data and asserted that it validates SHI correlation to crop yields and sensitivity to management as measured by the Comprehensive Assessment of Soil Health (CASH). We respond to van Es and Karlen with a more representative analysis of our data showing that individual SHI measurements are not predictive of crop yield from the 30‐yr North Carolina agronomic trial. Regressions for aggregate stability ( r 2 = 0.07) and P ( r 2 = 0.18) show that neither SHI sufficiently predicts corn yield for this dataset and show no obvious pattern based on tillage intensity. Relationships between corn ( Zea mays L.) yield and most biological SHI had r 2 ≤ 0.18, with only soil protein being moderately predictive of corn yield ( r 2 = 0.45). The CASH index to assess overall soil health by integrating physical, chemical, and biological SHI measurements into a single value of soil health is also not predictive of corn yield in the trial ( r 2 = 0.12). It is possible that current sampling and analytical procedures for assessing soil health do not consistently detect differences in productivity from soils with regional differences in land and ecological resources. We believe that calibrating SHI assessments to quantifiable agroecological outcomes instead of statistical rankings will reduce bias across regions and create a more inclusive framework for quantifying soil health.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Roper, Wayne R. and Osmond, Deanna L. and Heitman, Joshua L.}, year={2019}, pages={1842–1845} }
 @article{tian_kojima_heitman_horton_ren_2019, title={Advances in Thermo-Time Domain Reflectometry Technique: Measuring Ice Content in Partially Frozen Soils}, volume={4}, ISSN={2377-8741}, url={http://dx.doi.org/10.2136/msa2019.0003}, DOI={10.2136/msa2019.0003}, number={1}, journal={Methods of Soil Analysis}, publisher={Soil Science Society of America}, author={Tian, Zhengchao and Kojima, Yuki and Heitman, Joshua L. and Horton, Robert and Ren, Tusheng}, year={2019}, pages={0} }
 @article{tian_kool_ren_horton_heitman_2019, title={Approaches for estimating unsaturated soil hydraulic conductivities at various bulk densities with the extended Mualem-van Genuchten model}, volume={572}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2019.03.027}, abstractNote={The Mualem-van Genuchten model has been widely used for estimating unsaturated soil hydraulic conductivity (Ku) from measured saturated hydraulic conductivity (Ks) and fitted water retention curve (WRC) parameters. Soil bulk density (ρb) variations affect the accuracy of Ku estimates. In this study, we extend the Mualem-van Genuchten model to account for the ρb effect with ρb-related WRC and Ks models. We apply two functions (A and B) that relate the van Genuchten WRC model to ρb and two models (1 and 2) that estimate Ks with various ρb. By combining the ρb-related WRC functions and Ks models, we develop four integrated approaches (i.e., A1, A2, B1, and B2) for estimating Ku at various ρb. Ku measurements made on five soils with various textures and ρb are used to evaluate the accuracy of the four approaches. The results show that all approaches produce reasonable Ku estimates, with average root mean square errors (RMSEs) less than 0.35 (expressed in dimensionless unit because logarithmic Ku values are used). Approach A2, with an average RMSE of 0.25, agrees better with Ku measurements than does Approach A1 that has an average RMSE of 0.28. This is because Model 2 accounts for the WRC shape effect near saturation. Approaches A1 and A2 give more accurate Ku estimates than do Approaches B1 and B2 which both have average RMSEs of 0.35, because Function A performs better in estimating WRCs than does Function B. The proposed approaches could be incorporated into simulation models for improved prediction of water, solute, and gas transport in soils.}, journal={JOURNAL OF HYDROLOGY}, author={Tian, Zhengchao and Kool, Dilia and Ren, Tusheng and Horton, Robert and Heitman, Joshua L.}, year={2019}, month={May}, pages={719–731} }
 @article{roper_robarge_osmond_heitman_2019, title={Comparing Four Methods of Measuring Soil Organic Matter in North Carolina Soils}, volume={83}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2018.03.0105}, abstractNote={Core Ideas Results of agronomic management effects on SOM are inconsistent among methods. Correlations among methods of measuring SOM differ depending on soil. Soil organic matter content should be compared using similar procedures. Soil organic matter (SOM) provides many beneficial soil ecosystem services for sustainable soil management, but it is unclear how results from different methods of measuring SOM should be compared when making soil management decisions. To compare different methods, we used 84 soil samples from long-term agronomic trials in the coastal plain, piedmont, and mountain regions of North Carolina. Coastal plain and mountain trials included combinations of tillage and management (conventional vs. organic), whereas piedmont trials were configured to evaluate tillage intensity. The methods used to measure SOM were Walkley-Black (WB), mass loss on ignition (LOI), automated dry combustion (ADC), and humic matter (HM) colorimetry. Correlations among LOI, WB, and ADC were significant (p < 0.0001) for SOM measured from the total population of soils, but variability due to location implied that HM had no correlation to other methods. For measures of soil organic carbon compared to SOM, the WB results were biased high compared to ADC, and ADC was more strongly correlated to LOI than WB. When using the methods to evaluate the effects of agronomic management on SOM, results varied for different methods and locations. Conservation management did not consistently accumulate more SOM than other soil management practices, and no method consistently differentiated soils based on management. Variation in the composition of SOM measured using conventional methods may be causing discrepancies in reported changes in SOM content over time. To avoid confusion about how agronomic management affects SOM, assessments should limit comparisons to methodologies with similar measurement protocols.}, number={2}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Roper, Wayne R. and Robarge, Wayne P. and Osmond, Deanna L. and Heitman, Joshua L.}, year={2019}, pages={466–474} }
 @article{spivey_edmisten_wells_jordan_heitman_wilkerson_2019, title={Cotton Development and Yield Response to Irrigation, Planting Date, and Cultivar in North Carolina}, volume={23}, journal={Journal of Cotton Science}, author={Spivey, T.A. and Edmisten, K.L. and Wells, R. and Jordan, D. and Heitman, J.L. and Wilkerson, G.G.}, year={2019}, pages={148–160} }
 @article{spivey_edmisten_wells_jordan_heitman_wilkerson_2019, title={Cotton Growth and Yield Response to Short-Term Tillage Systems and Planting Date in North Carolina}, volume={23}, journal={Journal of Cotton Science}, author={Spivey, T.A. and Edmisten, K.L. and Wells, R. and Jordan, D. and Heitman, J.L. and Wilkerson, G.G.}, year={2019}, pages={270–283} }
 @article{fu_tian_amoozegar_heitman_2019, title={Measuring dynamic changes of soil porosity during compaction}, volume={193}, ISSN={0167-1987}, url={http://dx.doi.org/10.1016/j.still.2019.05.016}, DOI={10.1016/j.still.2019.05.016}, abstractNote={Soil porosity and pore-size distribution changes in response to compaction are important for heat, water, and air flow in soils. In this study, we used the thermo-time domain reflectometry (thermo-TDR) technique to investigate dynamics of in-situ soil porosity and pore-size distribution as affected by number of traffic passes, water content and soil depth. The study was conducted at a field site located near Clayton, NC, USA. A roller was dragged across the length of a 3- by 12-m plot three to five times to repeatedly compact the soil after tillage. Nine thermo-TDR probes, installed at 2.5-, 7.5-, and 12.5-cm depths (representing 0–5, 5–10, and 10–15 cm depth intervals, respectively) at three locations within the plot, were used to determine dynamic changes in soil porosity after each compaction event. Pore-size distribution changes within the top soil layer were determined for a subset of conditions by measuring in-situ infiltration at low tension using a mini disk infiltrometer. Nine core samples were also collected (considered to be a destructive method) near each thermo-TDR probe for measuring total porosity and water content after each compaction. Results showed that the thermo-TDR technique can accurately monitor the change of soil porosity during soil compaction compared to the destructive core method. Variability of replicated soil porosity measurements by the thermo-TDR technique (with a root mean square error (RMSE) of 0.011 m3 m−3 and mean standard error (MSE) of 0.010 m3 m−3) was lower than that of the core method (RMSE = 0.017 m3 m−3, MSE = 0.019 m3 m−3). As expected, total soil porosity decreased with the number of passes; a major portion of compaction (59–89% of the total porosity decrease) occurred during the first pass. The trend of topsoil (0–5 cm) compaction differed from that of subsoil layers (5–10 and 10–15 cm). Changes in porosity were highly sensitive to soil water content. For the sandy-textured soil in this study, soil porosity decreased as water content increased (during compaction period), and the maximum compaction (associated with the lowest porosity) was reached at an initial water content range between 0.08 and 0.10 g g-1. Above this range, the compaction level decreased with increasing water content. In addition, there was a shift in pore-size distribution for the surface layer. More importantly, pore-size distribution continued to change with additional traffic passes even after soil total porosity became stable.}, journal={Soil and Tillage Research}, publisher={Elsevier BV}, author={Fu, Yongwei and Tian, Zhengchao and Amoozegar, Aziz and Heitman, Josh}, year={2019}, month={Oct}, pages={114–121} }
 @article{kool_tong_tian_heitman_sauer_horton_2019, title={Soil water retention and hydraulic conductivity dynamics following tillage}, volume={193}, ISSN={0167-1987}, url={http://dx.doi.org/10.1016/j.still.2019.05.020}, DOI={10.1016/j.still.2019.05.020}, abstractNote={Soil bulk density (ρb) may be purposely reduced in agricultural fields using tillage to improve hydraulic properties. However, tillage alters the soil structure, resulting in unstable soils. As the soil stabilizes, ρb increases over time. While this is known, studies on soil hydraulic properties in tilled soils, including comparisons between tilled and non-tilled soils, commonly assume a rigid soil structure. This study presents changes in soil water retention and saturated hydraulic conductivity (Ksat) as ρb increased dynamically with time following tillage at a loam-textured field site. Over the summer of 2015, soil cores were collected at several depths below the surface following precipitation events. Soil water retention curves and Ksat were determined using pressure cells and the constant head method, respectively. Tillage reduced ρb to 0.94 g cm−3. Changes in ρb increased with depth, reaching a ρb of 1.11 g cm−3 in the 0–5 cm layer, and a ρb of 1.42 g cm−3 at the deepest tilled layer. Soil water retention curves were markedly steeper for samples with higher ρb, indicating an overall increase in water retained at a soil matric potential (Ψ) of −33 kPa. Evaluation of two modeling approaches for water retention as a function ρb indicated that changes in water retention with increases in ρb could be reasonably estimated if a matching point was used. No clear relationship between Ksat and ρb was obvious for ρb < 1.06 cm3 cm−3, but for ρb > 1.06 cm3 cm−3, Ksat decreased markedly (order of magnitude) as ρb increased. Hydraulic properties varied strongly depending on time since tillage and soil depth, and results have implications for models of tilled soils, as well as for studies comparing tilled and non-tilled soils.}, journal={Soil and Tillage Research}, publisher={Elsevier BV}, author={Kool, D. and Tong, B. and Tian, Z. and Heitman, J.L. and Sauer, T.J. and Horton, R.}, year={2019}, month={Oct}, pages={95–100} }
 @article{dold_heitman_giese_howard_havlin_sauer_2019, title={Upscaling Evapotranspiration with Parsimonious Models in a North Carolina Vineyard}, volume={9}, ISSN={2073-4395}, url={http://dx.doi.org/10.3390/agronomy9030152}, DOI={10.3390/agronomy9030152}, abstractNote={Water stress can positively or negatively impact grape yield and yield quality, and there is a need for wine growers to accurately regulate water use. In a four-year study (2010–2013), energy balance fluxes were measured with an eddy-covariance (EC) system in a North Carolina vineyard (Vitis vinifera cv. Chardonnay), and evapotranspiration (ET) and the Crop Water Stress Index (CWSI) calculated. A multiple linear regression model was developed to upscale ET using air temperature (Ta), vapor pressure deficit (VPD), and Landsat-derived Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI). Daily ET reached values of up to 7.7 mm day−1, and the annual ET was 752 ± 59 mm, as measured with the EC system. The grapevine CWSI was between 0.53–0.85, which indicated moderate water stress levels. Median vineyard EVI was between 0.22 and 0.72, and the EVI range (max–min) within the vineyard was 0.18. The empirical models explained 75%–84% of the variation in ET, and all parameters had a positive linear relationship to ET. The Root Mean Square Error (RMSE) was 0.52–0.62 mm. This study presents easily applicable approaches to analyzing water dynamics and ET. This may help wine growers to cost-effectively quantify water use in vineyards.}, number={3}, journal={Agronomy}, publisher={MDPI AG}, author={Dold, Christian and Heitman, Joshua and Giese, Gill and Howard, Adam and Havlin, John and Sauer, Tom}, year={2019}, month={Mar}, pages={152} }
 @article{tian_gao_kool_ren_horton_heitman_2018, title={Approaches for Estimating Soil Water Retention Curves at Various Bulk Densities With the Extended Van Genuchten Model}, volume={54}, ISSN={["1944-7973"]}, DOI={10.1029/2018WR022871}, abstractNote={Soil bulk density (ρb) variations influence soil hydraulic properties, such as the water retention curve (WRC), but they are usually ignored in soil water simulation models. We extend the van Genuchten WRC model parameters to account for ρb variations using a series of empirical expressions. WRC measurements made on eight soils with various ρb, and textures are used to calibrate these ρb-related empirical equations. Accordingly, two approaches are developed to estimate WRCs of soils at various ρb. Another eight soils with a wide range of ρb and textures are used to evaluate the accuracy of the new approaches. Approach 1 estimates WRCs for each soil at various ρb using a WRC measurement made at a reference ρb and the soil texture fractions. This approach gives reasonable WRC estimates for the eight validation soils, with an average root-mean-square error (RMSE) of 0.025 m3/m3 and an average determination coefficient (R2) of 0.94. For Approach 2, a WRC measurement made at a reference ρb and one additional water content-matric potential value measured at a different ρb value are used, which produces WRC estimates with an average RMSE of 0.017 m3/m3 and an average R2 of 0.97. The methodology used in Approach 2 is also applied to the Brooks and Corey WRC model to obtain accurate and precise WRC estimates. The proposed approaches have the potential to be incorporated into simulation models for estimating soil hydraulic properties that are affected by transient and variable ρb.}, number={8}, journal={WATER RESOURCES RESEARCH}, author={Tian, Zhengchao and Gao, Weida and Kool, Dilia and Ren, Tusheng and Horton, Robert and Heitman, Joshua L.}, year={2018}, month={Aug}, pages={5584–5601} }
 @article{kustas_agam_alfieri_mckee_prueger_hipps_howard_heitman_2018, title={Below canopy radiation divergence in a vineyard: implications on interrow surface energy balance}, volume={37}, ISSN={0342-7188 1432-1319}, url={http://dx.doi.org/10.1007/s00271-018-0601-0}, DOI={10.1007/s00271-018-0601-0}, number={3}, journal={Irrigation Science}, publisher={Springer Science and Business Media LLC}, author={Kustas, W. P. and Agam, N. and Alfieri, J. G. and McKee, L. G. and Prueger, J. H. and Hipps, L. E. and Howard, A. M. and Heitman, J. L.}, year={2018}, month={Oct}, pages={227–237} }
 @article{kojima_heitman_sakai_kato_horton_2018, title={Bulk density effects on soil hydrologic and thermal characteristics: A numerical investigation}, volume={32}, ISSN={["1099-1085"]}, DOI={10.1002/hyp.13152}, abstractNote={Abstract Soil bulk density (ρ b ) is commonly treated as static in studies of land surface dynamics. Magnitudes of errors associated with this assumption are largely unknown. Our objectives were to (a) quantify ρ b effects on soil hydrologic and thermal properties and (b) evaluate effects of ρ b on surface energy balance and heat and water transfer. We evaluated 6 soil properties, volumetric heat capacity, thermal conductivity, soil thermal diffusivity, water retention characteristics, hydraulic conductivity, and vapour diffusivity, over a range of ρ b , using a combination of 6 models. Thermal conductivity, water retention, hydraulic conductivity, and vapour diffusivity were most sensitive to ρ b , each changing by fractions greater than the associated fractional changes in ρ b . A 10% change in ρ b led to 10–11% change in thermal conductivity, 6–11% change in saturated and residual water content, 49–54% change in saturated hydraulic conductivity, and 80% change in vapour diffusivity. Subsequently, 3 field seasons were simulated with a numerical model (HYDRUS‐1D) for a range of ρ b values. When ρ b increased 25% (from 1.2 to 1.5 Mg m −3 ), soil temperature variation decreased by 2.1 °C in shallow layers and increased by 1 °C in subsurface layers. Surface water content differed by 0.02 m 3 m −3 for various ρ b values during drying events but differences mostly disappeared in the subsurface. Matric potential varied by >100 m of water. Surface energy balance showed clear trends with ρ b . Latent heat flux decreased 6%, sensible heat flux increased 9%, and magnitude of ground heat flux varied by 18% (with a 25% ρ b increase). Transient ρ b impacted surface conditions and fluxes, and clearly, it warrants consideration in field and modelling investigations.}, number={14}, journal={HYDROLOGICAL PROCESSES}, author={Kojima, Yuki and Heitman, Joshua L. and Sakai, Masaru and Kato, Chihiro and Horton, Robert}, year={2018}, month={Jul}, pages={2203–2216} }
 @article{o’brien_desutter_casey_daigh_heitman_derby_khan_2018, title={Daytime Surface Energy Fluxes over Soil Material Remediated Using Thermal Desorption}, volume={1}, ISSN={2639-6696}, url={http://dx.doi.org/10.2134/age2018.08.0027}, DOI={10.2134/age2018.08.0027}, abstractNote={Core Ideas Surface energy balance was quantified with micro‐Bowen ratio instrumentation. Surface energy balance was similar over native topsoil and soils treated with thermal desorption. Thermal desorption did not alter soil temperature dynamics or evaporation. A mix of topsoil and thermal desorption–treated soil matched surface energy balance of topsoil best. Remediation efforts to reduce contaminant concentrations in soils often alter soil properties. Since these alterations can affect the capacity of soil to function, their extent and magnitude may dictate future land use. This study addresses the suitability of soils for agricultural production after remediation of petroleum hydrocarbons using ex situ thermal desorption by quantifying the daytime surface energy balance prior to the growing season. The energy balance was quantified using micro‐Bowen ratio instrumentation to compare non‐contaminated topsoil (A) to both subsoil materials treated by thermal desorption (TD) and a 1:1 mixture (v/v) of TD and A (TDA). Despite differences in soil characteristics, the net radiation, soil heat flux, latent heat flux, and sensible heat flux were each similar among the three reclamation conditions over a period of 18 d. The fluctuations in these fluxes between the three conditions were attributed to natural variability, and they were not large enough to induce apparent inconsistencies in soil temperature dynamics or evaporative losses. Overall, these findings suggest the surface energy balance in thermal desorption–treated soils is similar to that of the native topsoil and that using a mixture of treated soils with native topsoil may even be a better representation of pre‐disturbance conditions.}, number={1}, journal={Agrosystems, Geosciences & Environment}, publisher={Wiley}, author={O’Brien, Peter L. and DeSutter, Thomas M. and Casey, Francis X. M. and Daigh, Aaron L.M. and Heitman, Joshua L. and Derby, Nathan E. and Khan, Eakalak}, year={2018}, month={Nov}, pages={180027} }
 @article{tian_kool_ren_horton_heitman_2018, title={Determining in-situ unsaturated soil hydraulic conductivity at a fine depth scale with heat pulse and water potential sensors}, volume={564}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2018.07.052}, abstractNote={Abstract Unsaturated hydraulic conductivity (K) of surface soil changes substantially with space and time, and it is of great importance for many ecological, agricultural, and hydrological applications. In general, K is measured in the laboratory, or more commonly, predicted using soil water retention curve and saturated hydraulic conductivity. In the field, K can be determined through infiltration experiments. However, none of these approaches are capable of continuously monitoring K in-situ at fine depth scales. In this study, we propose and investigate an approach to continuously estimate fine depth-scale K dynamics under field conditions. Evaporation rate and change in water storage in a near-surface soil layer are measured with the heat pulse method. Then, water flux density at the lower boundary of the soil layer is estimated from evaporation rate, change in water storage, and rainfall or irrigation rate using a simple water balance approach. Finally, K values at different soil depths are derived using the Buckingham-Darcy equation from water flux densities and measured water potential gradients. A field experiment is performed to evaluate the performance of the proposed approach. K values at 2-, 4-, 7.5-, and 12.5-cm depths are estimated with the new approach. The results show that in-situ K estimates vary with time following changes in soil water content, and the K-water content relationship changes with depth due to the difference in bulk density. In-situ estimated K-matric potential curves agree well with those measured in the laboratory. In-situ K estimates also show good agreement with the Mualem-van Genuchten model predictions, with an average root mean square error in log10 (K, mm h−1) of 0.54 and an average bias of 0.17. The new approach provides reasonable in-situ K estimates and has potential to reveal the influences of natural soil conditions on hydraulic properties as they change with depth and time.}, journal={JOURNAL OF HYDROLOGY}, author={Tian, Zhengchao and Kool, Dilia and Ren, Tusheng and Horton, Robert and Heitman, Joshua L.}, year={2018}, month={Sep}, pages={802–810} }
 @article{tian_lu_ren_horton_heitman_2018, title={Improved thermo-time domain reflectometry method for continuous in-situ determination of soil bulk density}, volume={178}, ISSN={["1879-3444"]}, DOI={10.1016/j.still.2017.12.021}, abstractNote={Abstract Quantifying the dynamics of surface soil bulk density (ρb) is important for characterizing water, heat, and gas exchanges in agricultural and environmental applications. Unfortunately, very few approaches are available for continuous in-situ monitoring of ρb. The soil heat capacity-based (C-based) thermo-time domain reflectometry (thermo-TDR) approach has been used to measure ρb in-situ, but this approach gives ρb estimates with relatively large errors. In this study, we present a new soil thermal conductivity-based (λ-based) thermo-TDR approach for continuous and automatic determination of ρb variation in-situ. An error analysis, literature data, and field experiments were used to evaluate the performance of the C-based and λ-based approaches. The error analysis undertaken on hypothetical soils indicated that the new λ-based approach was less sensitive to errors in the measurement inputs than was the C-based approach when the same relative errors occurred, except on very dry soils. Thermo-TDR measurements reported in the literature on seven soils showed that the new λ-based approach provided more accurate and precise ρb estimates, with coefficient of determination (R2) of 0.70 and root mean square error (RMSE) of 0.103 Mg m−3, than did the C-based approach which gave ρb with R2 of 0.32 and RMSE of 0.178 Mg m−3. Two field experiments were conducted to test the performance of the new λ-based thermo-TDR approach for monitoring ρb dynamics. The results showed that following tillage surface ρb increased by about 35% within 40 days. The ρb obtained by the λ-based thermo-TDR approach agreed well with independent core sampling measurements, with an average RMSE of 0.122 Mg m−3. The C-based approach failed to give acceptable ρb estimates in most cases because of probe deflection and environmental factors. We conclude that the new λ-based thermo-TDR approach is a promising method for continuous in situ measurements of ρb.}, journal={SOIL & TILLAGE RESEARCH}, author={Tian, Zhengchao and Lu, Yili and Ren, Tusheng and Horton, Robert and Heitman, Joshua L.}, year={2018}, month={May}, pages={118–129} }
 @article{rosas-anderson_taggart_heitman_miller_sinclair_rufty_2018, title={Partitioning between evaporation and transpiration from Agrostis stolonifera L. during light and dark periods}, volume={260}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2018.05.018}, abstractNote={Pressures on water availability for irrigation of turfgrasses continue in many parts of the United States as climate and weather patterns shift and populations increase. It is essential to understand underlying factors controlling water loss to more precisely predict irrigation requirements and develop new strategies for improving effective use of water. In this study, we investigate two key components of potential water loss from a bentgrass (Agrostis stolonifera L.) system that have not previously been examined in detail: 1) water loss in darkness, and 2) water loss through evaporation directly from the soil. The experiments were conducted in controlled environment chambers with intact cores from the field. An automated gravimetric system and soil moisture probes allowed precise measurements of water loss over ranges of vapor pressure deficits (VPD). The gravimetric and soil probe results indicated that substantial evapotranspiration occurred in darkness, at rates 40 to 60% of that in the light across VPDs. Simulations using field weather data from dry and humid environments indicated nighttime water loss rates would be expected to be 30 to 40% of that in the light. Using cores treated with a fast-acting, desiccating herbicide that eliminated transpiration but kept core resistances intact, evaporation directly from the soil surface was estimated to account for 40% of total water loss in the light and 60 to 70% in the dark. The results, collectively, indicated that water loss in darkness must be separately accounted for to accurately estimate daily evapotranspiration totals and irrigation requirements. Furthermore, because of the very high potential for evaporative water loss in the light and dark, efforts to improve water use efficiencies in the turfgrass system should include strategies that regulate both transpiration by the plant and evaporation from the soil surface.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Rosas-Anderson, Pablo and Taggart, Matthew J. and Heitman, Joshua L. and Miller, Grady L. and Sinclair, Thomas R. and Rufty, Thomas W.}, year={2018}, month={Oct}, pages={73–79} }
 @article{arya_heitman_2018, title={Response to "Comment on 'A Non-Empirical Method for Computing Pore Radii and Soil Water Characteristics from Particle Size Distribution' by Arya and Heitman (2015)"}, volume={82}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2018.01.0063r}, abstractNote={Soil Science Society of America JournalVolume 82, Issue 6 p. 1595-1596 Response Response to “Comment on ‘A Non-Empirical Method for Computing Pore Radii and Soil Water Characteristics from Particle Size Distribution’ by Arya and Heitman (2015)” Lalit M. Arya, Lalit M. Arya Soil consultant, Oceanside, CA, 92057Search for more papers by this authorJoshua L. Heitman, Corresponding Author Joshua L. Heitman josh_heitman@ncsu.edu Soil Science Department, North Carolina State University, Raleigh, NC, 27601Corresponding author (josh_heitman@ncsu.edu).Search for more papers by this author Lalit M. Arya, Lalit M. Arya Soil consultant, Oceanside, CA, 92057Search for more papers by this authorJoshua L. Heitman, Corresponding Author Joshua L. Heitman josh_heitman@ncsu.edu Soil Science Department, North Carolina State University, Raleigh, NC, 27601Corresponding author (josh_heitman@ncsu.edu).Search for more papers by this author First published: 25 October 2018 https://doi.org/10.2136/sssaj2018.01.0063r All Rights reserved. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume82, Issue6November-December 2018Pages 1595-1596 RelatedInformation}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Arya, Lalit M. and Heitman, Joshua L.}, year={2018}, pages={1595–1596} }
 @article{kojima_heitman_noborio_ren_horton_2018, title={Sensitivity analysis of temperature changes for determining thermal properties of partially frozen soil with a dual probe heat pulse sensor}, volume={151}, ISSN={["1872-7441"]}, DOI={10.1016/j.coldregions.2018.03.022}, abstractNote={Determining thermal conductivity (λ) and volumetric heat capacity (C) of partially frozen soils with a dual probe heat pulse (DPHP) sensor is challenging because an applied heat pulse melts ice surrounding the heater probe. Examining DPHP temperature changes with a commonly-used analytical solution that only accounts for heat conduction leads to inaccurate λ and C estimates for partially frozen soils at temperatures between −5 °C and 0 °C. In order to determine λ and C accurately and simultaneously, it is necessary to understand how various properties of partially frozen soil influence the temperature changes produced by DPHP sensors. The objective of this study is to determine the sensitivity of DPHP temperature changes to soil conditions and soil thermal properties. A numerical solution for radial heat conduction with soil freezing and thawing is developed. A series of simulations are performed, in which various errors are imposed onto a selected model parameter while other model parameters are held constant, and sensitivity coefficient values (φ) of the time of maximum probe temperature (tm) and of the maximum probe temperature rise (Tm) for each parameter are calculated. Temperature changes at the measurement probe are quite sensitive to initial soil temperature (φ values for tm and for Tm are −0.99 and 0.99, respectively), λ (φ value for tm is −0.93), and parameters determining the shape of the soil freezing characteristic (FC) curve, i.e., saturated water content θs (φ values for tm and for Tm are 0.59 and −0.73, respectively) and n (φ values for tm and for Tm are −2.7 and 2.4, respectively). Temperature changes are not very sensitive to C (φ values for tm and for Tm are 0.034 and −0.15, respectively). Although previous investigations tried to determine C by inverse analysis, this sensitivity analysis shows that the influence of C on temperature response to a heat pulse is masked by that of the FC. Thus, λ and FC parameters are the best candidate parameters to be determined by inverse analysis of DPHP data. This new result will guide further testing of DPHP sensors in partially frozen soils.}, journal={COLD REGIONS SCIENCE AND TECHNOLOGY}, author={Kojima, Yuki and Heitman, Joshua L. and Noborio, Kosuke and Ren, Tusheng and Horton, Robert}, year={2018}, month={Jul}, pages={188–195} }
 @article{zhang_ren_heitman_horton_2018, title={Summary of Advances in Heat-Pulse Methods: Measuring Near-Surface Soil Water Content}, volume={82}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2018.04.0138}, abstractNote={Core Ideas Describes the method for determining near‐surface water content with heat pulse sensors. Temperature data prior to a heat‐pulse are used to reduce ambient temperature effects. The PILS–ABC model is used to minimize errors because of the soil–air interface. Surface layer soil water content is important for evaporation, surface energy balance, seed germination, residue decomposition, microbial activity, and many other biological, chemical, and physical processes. The standard method (i.e., the gravimetric method) for measuring soil water content requires destructive sampling and is unsuitable for continuous measurement. Techniques such as neutron thermalization and time domain reflectometry suffer relatively large errors in measuring soil water content near the surface. In a recent Methods of Soil Analysis article, the authors present the principles and procedures for using a heat‐pulse sensor to determine near‐surface soil water content.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Zhang, Xiao and Ren, Tusheng and Heitman, Joshua and Horton, Robert}, year={2018}, pages={1015–1015} }
 @article{lu_liu_zhang_heitman_horton_ren_2018, title={Summary of Thermo-Time Domain Reflectometry Method: Advances in Monitoring In Situ Soil Bulk Density}, volume={82}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2018.01.0053}, abstractNote={Soil bulk density (ρb) is a key indicator of soil compaction and soil health that relates to water infiltration, plant rooting depth, nutrient availability, and soil microbial activity. Under field conditions, ρb usually varies with time and depth because of agronomic practices, root growth, and environmental processes (e.g., rainfall events, wetting/drying, and freezing/thawing). The traditional technique (i.e., the coring method) for determining ρb has the problems of destructive sampling, labor intensive, and is unable to capture the spatial and temporal variations. In a chapter of the recent Methods of Soil Analysis book, we present a review of the theory, instrumentation, and procedures of the thermo–time domain reflectometry (thermo-TDR) technique for monitoring in situ ρb (2). A thermo-TDR sensor (Fig. 1) measures soil thermal properties and water content (θ) concurrently by integrating the functions of the heat-pulse and TDR sensors. The method employs available models that relate heat capacity (C) or thermal conductivity (λ) to soil texture, θ, and ρb. With the prior information of sand/clay fractions and specific heat of soil solids, ρb is estimated inversely from θ and C or λ measurements made with thermo-TDR sensors. Laboratory and field tests have shown that the relative errors in ρb estimates are generally within 10%. The new method provides in situ and continuous ρb measurements with no calibration requirement, thus offers the potential for studying coupled heat and water processes in deformable soils where ρb changes with time and depth. Schematic view of the configuration for the 1 thermo-TDR sensor. The drawings are not to scale.}, number={4}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Lu, Yili and Liu, Xiaona and Zhang, Meng and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2018}, pages={733–733} }
 @article{kustas_anderson_alfieri_knipper_torres-rua_parry_nieto_agam_white_gao_et al._2018, title={THE GRAPE REMOTE SENSING ATMOSPHERIC PROFILE AND EVAPOTRANSPIRATION EXPERIMENT}, volume={99}, ISSN={["1520-0477"]}, DOI={10.1175/BAMS-D-16-0244.1}, abstractNote={Abstract Particularly in light of California’s recent multiyear drought, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sustainability of high-value crops. Providing this information requires the development of tools applicable across the continuum from subfield scales to improve water management within individual fields up to watershed and regional scales to assess water resources at county and state levels. High-value perennial crops (vineyards and orchards) are major water users, and growers will need better tools to improve water-use efficiency to remain economically viable and sustainable during periods of prolonged drought. To develop these tools, government, university, and industry partners are evaluating a multiscale remote sensing–based modeling system for application over vineyards. During the 2013–17 growing seasons, the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected micrometeorological and biophysical data within adjacent pinot noir vineyards in the Central Valley of California. Additionally, each year ground, airborne, and satellite remote sensing data were collected during intensive observation periods (IOPs) representing different vine phenological stages. An overview of the measurements and some initial results regarding the impact of vine canopy architecture on modeling ET and plant stress are presented here. Refinements to the ET modeling system based on GRAPEX are being implemented initially at the field scale for validation and then will be integrated into the regional modeling toolkit for large area assessment.}, number={9}, journal={BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY}, author={Kustas, William P. and Anderson, Martha C. and Alfieri, Joseph G. and Knipper, Kyle and Torres-Rua, Alfonso and Parry, Christopher K. and Nieto, Hector and Agam, Nurit and White, William A. and Gao, Feng and et al.}, year={2018}, month={Sep}, pages={1791–1812} }
 @article{basinger_jennings_monks_mitchem_chaudhari_heitman_havlin_howard_spayd_2018, title={Vegetation-Free Strip Width Affects Growth, Berry Composition, and Yield of Cabernet franc in Vigorous Growing Environments}, volume={2}, ISSN={2469-7974 2469-7974}, url={http://dx.doi.org/10.5344/catalyst.2018.17005}, DOI={10.5344/catalyst.2018.17005}, abstractNote={Summary Goals: In regions such as the eastern United States, excess vine vigor can be problematic. In this region, it is common to plant a perennial grass between rows, which can compete with vines for water and nutrients. The purpose of this research was to determine the effect of vegetation-free strip (VFS) width beneath the planted row on vine growth and fruit quality. The current recommendation for VFS width is 90 to 120 cm. However, modification of the VFS width can provide additional competition, limiting vine vigor. Determining the optimal width and effect of the VFS on vine size, berry composition, and yield would allow growers to optimize groundcover management in this region. Key Findings: Reducing VFS width decreased pruning weight/m cordon, shoot number/m cordon, lateral shoot number/cane, and summer fresh hedging weights. Narrowing the VFS width was most effective in the two of four years with the least rainfall. Yield/m cordon was reduced by narrowing VFS width, but not to below normal adjusted crop loads. Cluster weight, number of berries/cluster, and cluster number/m cordon were also reduced by narrowing VFS width. Berry soluble solids and total anthocyanins increased and TA decreased with decreasing VFS width, improving berry quality. Postveraison natural weed population growth in the VFS did not affect vine growth or fruit yield and composition. Impact and Significance: In the eastern United States, high rainfall and humidity promote excessive vine growth and immense pest pressure for Vitis vinifera production. Improved canopy characteristics could increase fruit quality by reducing pest pressure, by increasing soluble solids and total anthocyanin concentrations, and by improving the balance between pH and titratable acidity (TA). Increasing competition for water and nutrients during the growing season (by narrowing the VFS or allowing late-season weed competition) may be an effective way to accomplish these improvements. In this study, narrower VFS width in a tall fescue ( Festuca arundinacea var. ‘Kentucky 31’) groundcover reduced vine vegetative growth and positively influenced berry composition. Vineyard weed populations that established naturally postveraison did not affect vine size, yield, or fruit quality.}, number={1}, journal={Catalyst: Discovery into Practice}, publisher={American Society for Enology and Viticulture}, author={Basinger, Nicholas T. and Jennings, Katherine M. and Monks, David W. and Mitchem, Wayne E. and Chaudhari, Sushila and Heitman, Joshua L. and Havlin, John L. and Howard, Adam M. and Spayd, Sara E.}, year={2018}, month={Jun}, pages={15–23} }
 @article{mohammadshirazi_mclaughlin_heitman_brown_2017, title={A multi-year study of tillage and amendment effects on compacted soils}, volume={203}, ISSN={["1095-8630"]}, DOI={10.1016/j.jenvman.2017.07.031}, abstractNote={Constructing roads and buildings often involves removal of topsoil, grading, and traffic from heavy machinery. The result is exposed, compacted subsoil with low infiltration rate (IR), which hinders post-construction vegetation establishment and generates significant runoff, similar to impervious surfaces. Our goal was to assess tillage and adding amendments for improving density and maintaining perviousness of subsoils compacted during construction. The effects of tillage with and without amendments on (1) soil compaction, (2) IR, and (3) vegetative growth at five sites in North Carolina, USA were evaluated over a period of up to 32 months. The sites, representing a range of soil conditions, were located at three geographic regions; one in the Sandhills (located in Coastal Plain), one in the mountains, and three in the Piedmont. Amendments varied by site and included: (1) compost, (2) cross-linked polyacrylamide (xPAM), and (3) gypsum. Bulk density (BD) and soil penetration resistance (PR) tests were used to characterize soil physical condition. The IR was measured using a Cornell Sprinkle Infiltrometer. Vegetative growth was evaluated by measuring shoot mass and vegetative cover at all sites and root density at the Piedmont sites. Tillage decreased BD and PR compared to the compacted soil at four out of five sites for observations ranging from 24 to 32 months. Compost was applied to four sites prior to tillage and reduced BD in two of them compared to tillage alone. The IR in the tilled plots was maintained at about 3–10 times that of the compacted soil among the five sites over the monitoring periods. Adding amendments did not increase IR relative to tillage alone except at one Piedmont site, where compost and xPAM increased IR at 12 months and compost at 24 months after site establishment. Vegetative responses to tillage and amendments were inconsistent across sites. Results suggest that tillage is a viable option to reduce bulk density and increase infiltration for areas with compacted soils where vegetation is to be established, and that the effect is maintained for at least several years.}, journal={JOURNAL OF ENVIRONMENTAL MANAGEMENT}, author={Mohammadshirazi, Fatemeh and McLaughlin, Richard A. and Heitman, Joshua L. and Brown, Virginia K.}, year={2017}, month={Dec}, pages={533–541} }
 @article{zhang_ren_heitman_horton_2017, title={Advances in Heat-Pulse Methods: Measuring Near-Surface Soil Water Content}, volume={2}, ISSN={2377-8741}, url={http://dx.doi.org/10.2136/msa2015.0032}, DOI={10.2136/msa2015.0032}, number={1}, journal={Methods of Soil Analysis}, publisher={Soil Science Society of America}, author={Zhang, Xiao and Ren, Tusheng and Heitman, Joshua and Horton, Robert}, year={2017}, pages={0} }
 @article{heitman_zhang_xiao_ren_horton_2017, title={Advances in Heat-Pulse Methods: Measuring Soil Water Evaporation with Sensible Heat Balance}, volume={2}, ISSN={2377-8741}, url={http://dx.doi.org/10.2136/msa2015.0029}, DOI={10.2136/msa2015.0029}, number={1}, journal={Methods of Soil Analysis}, publisher={Soil Science Society of America}, author={Heitman, J.L. and Zhang, X. and Xiao, X. and Ren, T. and Horton, R.}, year={2017}, pages={0} }
 @article{vann_fisher_wells_jordan_heitman_2017, title={Alternative Ridging Practices for Flue-Cured Tobacco Production in North Carolina}, volume={3}, ISSN={2374-3832}, url={http://dx.doi.org/10.2134/cftm2017.02.0016}, DOI={10.2134/cftm2017.02.0016}, abstractNote={Core Ideas Alternative ridging methods could prove beneficial for tobacco producers. Conservation tillage efforts have demonstrated little success. Fine‐textured soils will require special management considerations. Soil resistance is considered to be a limiting production factor. Coarse‐textured soils appear to be better suited than fine‐textured soils. With increasing farm size and the necessity for timely field preparation, flue‐cured tobacco ( Nicotiana tabacum L.) producers in North Carolina would benefit from alternatives to current ridging practices. Research was conducted in 2012 and 2013 to evaluate the effects of differing ridging methods on soil physical properties and the growth and development of flue‐cured tobacco. In each environment, two alternative ridging methods were compared with the grower standard of spring ridging (SR): fall ridging (FR) and rotary ridging (RR) in the Piedmont, and FR and no ridging (NR) in the Coastal Plain. In the Piedmont, FR reduced leaf yield and value when compared with RR and SR systems. Reduced yield and value were a result of high soil resistance that inhibited plant growth. In the Coastal Plain, treatments imposed did not affect the soil physical properties or tobacco yield and quality. Results indicate that FR and NR systems are acceptable alternative ridging methods for the production of flue‐cured tobacco in the sandy Coastal Plain growing region. Alternatively, FR should not be used in the Piedmont growing region due to the fine soil texture that is prone to high resistance.}, number={1}, journal={Crop, Forage & Turfgrass Management}, publisher={Wiley}, author={Vann, Matthew C. and Fisher, Loren R. and Wells, Randy and Jordan, David L. and Heitman, Joshua L.}, year={2017}, month={Jun}, pages={cftm2017.02.0016} }
 @article{wang_zhang_xiao_heitman_horton_ren_2017, title={An Empirical Calibration for Heat-Balance Sap-Flow Sensors in Maize}, volume={109}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2016.10.0611}, abstractNote={Core Ideas Sap flow errors with heat‐balance sap‐flow sensors are quantified. An empirical equation is established for correcting heat‐balance sap‐flow measurements in maize. Independent tests proved the usefulness of the calibration equation in maize. Sap flow measurements with heat‐balance sap‐flow (HBSF) sensors are subject to errors due to temperature heterogeneity across the plant stem. Here we develop and evaluate an empirical calibration for HBSF sensors to measure transpiration rates ( T ) of maize ( Zea mays L.). A pot experiment was used to establish an empirical calibration equation relating T determined by a mass balance method and sap flow velocity ( V ) measured with HBSF sensors. The calibration equation was tested in a field weighing lysimeter study, a pot study from the literature, and an additional dataset where V was measured with HBSF sensors, and T was determined from independent measurements of evapotranspiration and evaporation. In all studies, HBSF sensor measured V overestimated T , and the errors displayed diurnal dynamics: small in the evening and early morning, became larger with increasing T , and reached a maximum when solar irradiance was the largest. A linear calibration equation, T’ = 0.65 V + 0.39, was established to convert measured V (g plant −1 h −1 ) values to corrected transpiration rates T’ (g plant −1 h −1 ). Using this equation, the largest sap flow error was reduced by 60, 50, and 50% in the lysimeter experiment, pot experiment, and field study, respectively.}, number={3}, journal={AGRONOMY JOURNAL}, author={Wang, Yueyue and Zhang, Xiao and Xiao, Xinhua and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2017}, pages={1122–1128} }
 @article{tian_ren_kojima_lu_horton_heitman_2017, title={An improved thermo-time domain reflectometry method for determination of ice contents in partially frozen soils}, volume={555}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/J.JHYDROL.2017.10.055}, DOI={10.1016/J.JHYDROL.2017.10.055}, abstractNote={Measuring ice contents (θi) in partially frozen soils is important for both engineering and environmental applications. Thermo-time domain reflectometry (thermo-TDR) probes can be used to determine θi based on the relationship between θi and soil heat capacity (C). This approach, however, is accurate in partially frozen soils only at temperatures below −5 °C, and it performs poorly on clayey soils. In this study, we present and evaluate a soil thermal conductivity (λ)-based approach to determine θi with thermo-TDR probes. Bulk soil λ is described with a simplified de Vries model that relates λ to θi. From this model, θi is estimated using inverse modeling of thermo-TDR measured λ. Soil bulk density (ρb) and thermo-TDR measured liquid water content (θl) are also needed for both C-based and λ-based approaches. A theoretical analysis is performed to quantify the sensitivity of C-based and λ-based θi estimates to errors in these input parameters. The analysis indicates that the λ-based approach is less sensitive to errors in the inputs (C, λ, θl, and ρb) than is the C-based approach when the same or the same percentage errors occur. Further evaluations of the C-based and λ-based approaches are made using experimentally determined θi at different temperatures on eight soils with various textures, total water contents, and ρb. The results show that the λ-based thermo-TDR approach significantly improves the accuracy of θi measurements at temperatures ≤−5 °C. The root mean square errors of λ-based θi estimates are only half those of C-based θi. At temperatures of −1 and −2 °C, the λ-based thermo-TDR approach also provides reasonable θi, while the C-based approach fails. We conclude that the λ-based thermo-TDR method can reliably determine θi even at temperatures near the freezing point of water (0 °C).}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Tian, Zhengchao and Ren, Tusheng and Kojima, Yuki and Lu, Yili and Horton, Robert and Heitman, Joshua L.}, year={2017}, month={Dec}, pages={786–796} }
 @article{peng_heitman_horton_ren_2017, title={Determining Near-Surface Soil Heat Flux Density Using the Gradient Method: A Thermal Conductivity Model-Based Approach}, volume={18}, ISSN={["1525-7541"]}, DOI={10.1175/jhm-d-16-0290.1}, abstractNote={Abstract In the gradient method, soil heat flux density at a known depth G is determined as the product of soil thermal conductivity λ and temperature T gradient. While measuring λ in situ is difficult, many field studies readily support continuous, long-term monitoring of soil T and water content θ in the vadose zone. In this study, the performance of the gradient method is evaluated for estimating near-surface G using modeled λ and measured T. Hourly λ was estimated using a model that related λ to θ, soil bulk density ρb, and texture at 2-, 6-, and 10-cm depths. Soil heat flux Gm was estimated from modeled λ and measured T gradient (from thermocouples). The Gm results were evaluated with heat flux data GHP determined using independent measured λ and T gradient from heat-pulse probes. The λ model performed well at the three depths with 3.3%–7.4% errors. The Gm estimates were similar to GHP (agreed to within 15.1%), with the poorest agreement at the 2-cm soil depth, which was caused mainly by the relatively greater variability in ρb. Accounting for temporal variations in ρb (with core method) improved the accuracies of λ and Gm at the 2-cm depth. Automated θ monitoring approaches (e.g., time domain reflectometry), rather than gravimetric sampling, captured the temporal dynamics of near-surface λ and G well. It is concluded that with continuous θ and T measurements, the λ model–based gradient method can provide reliable near-surface G. Under conditions of soil disturbance or deformation, including temporally variable ρb, data improves the accuracy of G data.}, number={8}, journal={JOURNAL OF HYDROMETEOROLOGY}, author={Peng, Xiaoyang and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2017}, month={Aug}, pages={2285–2295} }
 @misc{heitman_2017, title={Essential soil physics, an introduction to soil processes, functions, structure, and mechanics}, volume={182}, number={3}, journal={Soil Science}, author={Heitman, J. L.}, year={2017}, pages={114–114} }
 @article{wang_heitman_smyth_crozier_franzluebbers_gehl_lee_2017, title={Impact of Bioenergy Crop Production on North Carolina Piedmont Soil Properties}, volume={109}, journal={Agronomy Journal}, author={Wang, Z. and Heitman, J.L. and Smyth, T.J. and Crozier, C.R. and Franzluebbers, A. and Gehl, R. and Lee, S.}, year={2017}, pages={1–11} }
 @article{peng_wang_heitman_ochsner_horton_ren_2017, title={Measurement of soil-surface heat flux with a multi-needle heat-pulse probe}, volume={68}, ISSN={["1365-2389"]}, DOI={10.1111/ejss.12421}, abstractNote={Summary Soil‐surface heat flux ( G 0 ), an important component of the surface energy balance, is often determined by summing soil heat flux ( G z ) at a depth ( z ) below the surface and the rate of change in soil heat storage (Δ S ) in the layer above z . The soil heat flux G z is commonly measured with passive heat flux plates, but self‐calibrating plates or additional corrections are required to obtain accurate data. In some cases, Δ S is neglected because of the difficulty of monitoring the dynamics of volumetric heat capacity ( C ), which might lead to erroneous estimates of G 0 . To overcome these limitations, we introduce the heat‐pulse method for measuring G 0 with a multi‐needle heat‐pulse probe (HPP). Soil temperature ( T ) distribution, thermal conductivity (λ) and C of the 0–52‐mm layer were measured hourly on five consecutive days with an 11‐needle HPP, and G z at 50‐mm depth ( G 50 ) and Δ S of the 0–50‐mm layer (Δ S 0–50 ) were determined by the gradient and calorimetric methods, respectively. Independent measurements of G 50 with a self‐calibrating heat flux plate and Δ S 0–50 calculated with the de Vries model C were used to evaluate the HPP data. With reliable G 50 and Δ S 0–50 measurements, the HPP‐based G 0 data agreed well with those estimated from the independent method (with a mean absolute difference of 4.5 W m −2 ). Supporting measurements showed that determining G z at the 50‐mm depth minimized the likelihood of errors from evaporation below the measurement depth. The multi‐needle HPP provides a reliable way to determine G 0 in situ . Additional analysis demonstrated that by reducing the number of needles from 11 to 5, the datalogging requirement was reduced by half and G 0 was still determined with acceptable accuracy. Highlights Heat flux at the soil surface ( G 0 ) was monitored by the heat‐pulse technique. A multi‐needle heat‐pulse probe (HPP) was used to measure subsurface soil heat flux ( G z ) and heat storage concurrently. Appropriate measurement depths of G z were determined to minimize the effects of subsurface latent heat sink on G 0 . A simplified calculation reduced the datalogging requirement of the multi‐needle HPP.}, number={3}, journal={EUROPEAN JOURNAL OF SOIL SCIENCE}, author={Peng, X. and Wang, Y. and Heitman, J. . and Ochsner, T. and Horton, R. and Ren, T.}, year={2017}, month={May}, pages={336–344} }
 @article{roper_osmond_heitman_wagger_reberg-horton_2017, title={Soil Health Indicators Do Not Differentiate among Agronomic Management Systems in North Carolina Soils}, volume={81}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2016.12.0400}, abstractNote={Core Ideas Soil health metrics were not differentiated in long-term agronomic trials. Soil health tests produced different results and were not consistent with management. Soil health indicators should be tested in different agroecological regions. Recent soil tests evaluating “soil health” on a broad scale may not properly consider the intrinsic limitations of soil properties, and have not been assessed in regionally unique soil conditions. To evaluate three soil tests in North Carolina, we used long-term agronomic management trials from three distinct physiographic regions: mountain (22 yr), piedmont (32 yr), and coastal plain (17 yr). Mountain and coastal plain trials included combinations of organic or chemical management with or without tillage; the piedmont trial included nine different tillage treatments. Soil samples were collected and submitted for analysis as recommended by the North Carolina Department of Agriculture and Consumer Services, Haney soil health test (HSHT), and Cornell comprehensive assessment of soil health (CASH). Plant nutrient concentrations varied but were still sufficient for crops. The CASH physical soil indicators, such as surface hardness and aggregate stability, were not statistically different, regardless of tillage intensity or management. Biological soil indicators (e.g., CO2 respiration) responded differently to management, but this differentiation was inconsistent among locations and tests. Despite many years of conservation management, the CASH results described mountain soils as “low” or “very low” soil health for all but no-till organic management, which received a “medium” score. The HSHT results considered soil from all but moldboard plowing (piedmont) to be in good health. Finally, there was no correlation between soil health tests and crop yields from North Carolina soils. Soil health tests should be calibrated to better differentiate among soil management effects that vary depending on intrinsic soil limitations.}, number={4}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Roper, Wayne R. and Osmond, Deanna L. and Heitman, Joshua L. and Wagger, Michael G. and Reberg-Horton, S. Chris}, year={2017}, pages={828–843} }
 @article{wang_heitman_smyth_crozier_franzluebbers_lee_gehl_2017, title={Soil Responses to Bioenergy Crop Production in the North Carolina Piedmont}, volume={109}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2017.02.0068}, abstractNote={Core Ideas Three bioenergy and two traditional cropping systems were compared in the North Carolina Piedmont. Bioenergy crops sorghum, switchgrass, and giant mischanthus produced large yields. Removal of N, P, and K was least for perennial bioenergy crops. Perennial bioenergy crops had slightly poorer soil physical conditions after 3 yr. Organic C pools were greatest with giant miscanthus and fescue. Bioenergy crops are potential alternatives to traditional row‐crop and pasture/hay systems. A trial comparing effects of bioenergy to traditional production on soil properties was established in 2012 under no‐till in the North Carolina Piedmont. Five cropping systems included: giant miscanthus ( Miscanthus × giganteus ), switchgrass ( Panicum virgatum L.), biomass sorghum ( Sorghum bicolor spp.), tall fescue [ Schedonorus arundinaceus (Schreb.) Dumort.], and corn ( Zea mays L.)/wheat ( Triticum aestivum L.)/soybean ( Glycine max L.) rotation. Soil samples were collected before and 3 yr after trial establishment. Sorghum produced average yield of 21.5 Mg ha −1 in 2012 to 2015. Miscanthus and switchgrass reached yield plateaus of 21 and 15 Mg ha −1 , respectively, and removed significantly less N, P, and K than other crops, due to their rhizome systems and lower fertilizer requirements. They did not, however, demonstrate advantages over annual crops in soil physical properties. Soils under miscanthus and switchgrass had the least macropores and lowest saturated hydraulic conductivity. Summed to 30‐cm soil depth, miscanthus maintained similar soil organic C as with tall fescue (58.6 vs. 55.0 Mg C ha −1 ), whereas soil organic C under sorghum and switchgrass were lowest (average of 49.5 Mg ha −1 ). Microbial biomass soil C under miscanthus (0–12‐cm depth) was significantly greater than under annual crops. Negative effects of switchgrass on soil physical properties and organic C and N might have been due to tillage required for establishment. Typical bioenergy crops do not appear to have major negative or positive effects on soil properties in the North Carolina Piedmont.}, number={4}, journal={AGRONOMY JOURNAL}, author={Wang, Zan and Heitman, Joshua L. and Smyth, T. Jot and Crozier, Carl R. and Franzluebbers, Alan and Lee, Sage and Gehl, Ronald J.}, year={2017}, pages={1368–1378} }
 @article{zhang_lu_heitman_horton_ren_2017, title={Temporal Changes of Soil Water Retention Behavior as Affected by Wetting and Drying Following Tillage}, volume={81}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2017.01.0038}, abstractNote={Soil structure-dependent properties are subject to changes with time and depth under the influences of agronomic practices and environmental factors. Wetting and drying (W/D) cycles following tillage alter the structure and pore-related functions of field soils. This study investigates the effects of W/D cycles on temporal changes of soil porosity and water retention curves (SWRCs) of a tilled layer (0- to 15-cm) during a post-tillage period. Soil volumetric water content (θ) and matric potential (ψₘ) dynamics at three depths were monitored continuously, and the total porosity (Pₜ) was determined gravimetrically. Nine W/D cycles were identified in the experimental period. Soil Pₜ decreased gradually with time and depth and became relatively stable after four W/D cycles, and the SWRCs shifted toward higher θ values at a specific ψₘ. The magnitude of SWRC change was relatively small during the first to third W/D cycles when the degrees of saturation were relatively low, reached the maximum after the fourth W/D cycle during which the soil was nearly saturated, and became less significant thereafter. Soil water holding capacity was improved during the W/D processes mainly due to the reduction of effective porosity and development of residual porosity. During the earlier four W/D cycles, a higher initial θ also contributed to the increase of the residual porosity, and thus enhanced the soil water holding capacity. The difference, however, tended to disappear in later W/D cycles. The data show clearly that the θ–ψₘ relationships following tillage are dynamic.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Zhang, Meng and Lu, Yili and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2017}, pages={1288–1295} }
 @article{lu_liu_zhang_heitman_horton_ren_2017, title={Thermo–Time Domain Reflectometry Method: Advances in Monitoring In Situ Soil Bulk Density}, volume={2}, ISSN={2377-8741}, url={http://dx.doi.org/10.2136/msa2015.0031}, DOI={10.2136/msa2015.0031}, number={1}, journal={Methods of Soil Analysis}, publisher={Soil Science Society of America}, author={Lu, Yili and Liu, Xiaona and Zhang, Meng and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2017}, pages={0} }
 @article{fields_owen_stewart_heitman_2017, title={Utilizing the HYDRUS model as a tool for understanding soilless substrate water dynamics}, volume={7}, ISSN={0567-7572 2406-6168}, url={http://dx.doi.org/10.17660/actahortic.2017.1168.41}, DOI={10.17660/actahortic.2017.1168.41}, number={1168}, journal={Acta Horticulturae}, publisher={International Society for Horticultural Science (ISHS)}, author={Fields, J.S. and Owen, J.S., Jr. and Stewart, R.D. and Heitman, J.L.}, year={2017}, month={Jul}, pages={317–324} }
 @article{wang_ochsner_heitman_horton_xue_ren_2017, title={Weighing Lysimeter Data Confirm the Accuracy and Precision of the Heat-Pulse Technique for Measuring Daily Soil Evaporation}, volume={81}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2017.02.0049n}, abstractNote={Core Ideas Multi‐needle heat‐pulse probes are applied for measuring daily evaporation rate. Measurement accuracy and precision are confirmed with weighing lysimeter data. The probes provide a new way to monitor daily evaporation rate continuously. The heat‐pulse technique, which is based on the sensible heat balance, has been developed for measuring soil‐water evaporation ( E ). The accuracy and precision of the technique has been previously tested with the Bowen ratio method and micro‐lysimeters, which are themselves subject to considerable uncertainties. This study evaluated the accuracy and precision of the heat‐pulse technique using direct, continuous, and nondestructive E measurements from a weighing lysimeter. Multi‐needle heat‐pulse probes were installed in a silt loam soil at four locations in a 22.5‐m 3 (3‐m × 3‐m × 2.5‐m) weighing lysimeter to measure soil thermal conductivity, heat capacity, and temperature gradients in the 0‐ to 5‐cm layer. Daily E rates were estimated with sensible heat balance theory. Independent daily E rates obtained directly from a weighing lysimeter were used to evaluate the accuracy of heat‐pulse E estimates during a 10‐d drying period. Potential daily evaporation ( E 0 ) was also computed using the Penman–Monteith equation. The E / E 0 ratio was >0.9 for the first 4 d but fell sharply thereafter and approached a stable value of 0.4. There was a linear relationship between heat‐pulse values and weighing lysimeter values, with a slope of 0.95 and an offset of 0.09 mm d −1 . The absolute error of the heat‐pulse E ranged from −0.02 to 0.29 mm d −1 (or −1 to 8% of the true value), and the RMSE was 0.15 mm d −1 . The SD of the heat‐pulse E data ranged from 0.07 to 0.51 mm d −1 , and the coefficients of variation ranged from 3 to 14%. We concluded that the heat‐pulse technique can provide daily E measurements with good accuracy and precision.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Wang, Yueyue and Ochsner, Tyson and Heitman, Joshua and Horton, Robert and Xue, Xuzhang and Ren, Tusheng}, year={2017}, pages={1074–1078} }
 @article{lu_liu_heitman_horton_ren_2016, title={Determining Soil Bulk Density with Thermo-Time Domain Reflectometry: A Thermal Conductivity-Based Approach}, volume={80}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2015.08.0315}, abstractNote={The bulk density (ρb) of a tilled soil layer usually varies with depth and time. It is difficult to measure in situ ρb with available instruments. Here we present a new approach that is capable of monitoring in situ ρb based on thermal conductivity (λ) measurements. The proposed approach relies on an empirical model that relates λ to soil particle-size distribution, ρb, and volumetric water content (θ). The thermo-time domain reflectometry (thermo-TDR) sensor measures λ and θ simultaneously, and knowing soil texture a priori, ρb is estimated using the empirical model. The approach was tested using datasets obtained on repacked and intact soil samples with a wide range of ρb and θ. Further evaluations were made using in situ ρb measurements with thermo-TDR sensors in four tillage treatments. The laboratory results showed that the λ-based thermo-TDR method was able to provide reliable ρb with root mean square errors (RMSE) within 0.17 g cm⁻³. Under field conditions, the λ-based thermo-TDR method also provided accurate ρb estimates with relative error generally within 10%. Under both laboratory and field conditions, the λ-based thermo-TDR method performed better than the heat capacity (C)-based thermo-TDR method. Differences were attributed mainly to C errors resulting from probe deflections, while λ measurements with the thermo-TDR method were not affected by probe deflections. The λ-based approach provides a way to obtain nondestructive, repeated, and in situ ρb estimates with the thermo-TDR method both in laboratory and field settings.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Lu, Yili and Liu, Xiaona and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2016}, pages={48–54} }
 @article{mohammadshirazi_brown_heitman_mclaughlin_2016, title={Effects of tillage and compost amendment on infiltration in compacted soils}, volume={71}, ISSN={["1941-3300"]}, DOI={10.2489/jswc.71.6.443}, abstractNote={Soils are compacted during land development through soil excavation and heavy equipment traffic. Compacted soils have limited infiltration and are susceptible to erosion. Infiltration can be enhanced by various approaches including tillage and compost addition. The objective of this study was to determine the efficacy of tillage and adding compost to reduce stormwater runoff and sediment loss by improving infiltration in simulated postconstruction soils. Tillage treatments were tested at two sites in the Piedmont region of North Carolina (Piedmont 1 and 2). Prior to applying tillage and amendment, soils at both sites were graded to remove the surface horizon and compacted with a vibratory roller. At Piedmont 1, the treatments were compacted with no tillage, shallow (15 cm [5.9 in] depth) tillage (ST), and deep (30 cm [11.8 in] depth) tillage (DT). At Piedmont 2 the treatments were compacted, DT, and DT with incorporated compost (DT+Com). The grass seed mixtures recommended by the North Carolina Department of Transportation for the location (Piedmont) and time of planting were applied at each site. Runoff volumes (RV) and total suspended solids were measured after each of the first 12 and 13 storm events at Piedmont 1 and 2, respectively. Infiltration rate (IR) and bulk density (BD) were determined five and seven months after establishment at Piedmont 1 and 2, respectively. At both sites, RV and total amount of soil loss were reduced with tillage by 60% to 82% during the monitoring period. Neither deeper tillage nor incorporating compost significantly affected these results. Grass establishment was significantly better with tillage. The IRs measured at the end of the monitoring period were around 1 cm h<sup>−1</sup> (0.4 in hr<sup>−1</sup>) in the compacted treatment but ranged from 19 to 33 cm h<sup>−1</sup> (7.5 to 13 in hr<sup>−1</sup>) in the tilled treatments, again with no effects of tillage depth or compost. The results suggest that tillage to a depth of at least 15 cm (6 in) can be highly effective for improving soil conditions and reducing runoff and erosion from soils compacted as the result of construction activities.}, number={6}, journal={JOURNAL OF SOIL AND WATER CONSERVATION}, author={Mohammadshirazi, F. and Brown, V. K. and Heitman, J. L. and McLaughlin, R. A.}, year={2016}, pages={443–449} }
 @article{kool_kustas_ben-gal_lazarovitch_heitman_sauer_agam_2016, title={Energy and evapotranspiration partitioning in a desert vineyard}, volume={218}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2016.01.002}, abstractNote={The challenge of partitioning energy and evapotranspiration (ET) components was addressed over a season (bud break till harvest) in a wine grape vineyard located in an extreme arid region. A below canopy energy balance approach was applied to continuously estimate evaporation from the soil (E) while system ET was measured using eddy covariance. Below canopy energy balance was assessed at the dry midrow position as well as the wet irrigated position directly underneath the vine row, with E calculated as the residual of measured net radiation, soil heat flux, and computed sensible heat flux. The variables used to compute sensible heat flux included soil surface temperature measured using infrared thermometers and below-canopy wind speed in a soil resistance formulation that required a modified wind factor. The E derived from below canopy energy balance was reasonable at daily intervals although it underestimated micro-lysimeter E measurements, suggesting there may have been advected energy from the midrow to the below-vine position. Seasonal partitioning indicated that total E amounted to 9–11% of ET. In addition, empirical functions from the literature relating crop coefficients (Kcb) to plant size, appeared to give reasonable results under full canopy, albeit with some day to day variation, but underestimated Kcb during the growing period.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Kool, D. and Kustas, W. P. and Ben-Gal, A. and Lazarovitch, N. and Heitman, J. L. and Sauer, T. J. and Agam, N.}, year={2016}, month={Mar}, pages={277–287} }
 @article{kool_heitman_lazarovitch_agam_sauer_ben-gal_2016, title={In Situ Thermistor Calibration for Improved Measurement of Soil Temperature Gradients}, volume={80}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2016.05.0134}, DOI={10.2136/sssaj2016.05.0134}, abstractNote={Core Ideas Soil temperature gradients are important for soil (latent) heat flux estimation. Heat‐pulse sensor thermistors' temperature differences were on the order of 0.2°C. In situ calibration reduced uncertainty between thermistors to about 0.06°C. In situ calibrated offsets between thermistors were similar to laboratory results. Offsets were found to change very little over a 5‐yr period. Accurate measurement of soil temperature gradients is important for the estimation of soil heat flux and latent heat flux, both major components of the surface energy balance. Soil temperature gradients are commonly measured using heat‐pulse sensors equipped with thermistors. In this study, individual thermistors showed absolute temperature differences on the order of 0.2°C when placed under uniform temperature conditions. These differences compromised measurement of soil temperature gradients over small depth increments and/or conditions with relatively minor variation in temperatures. An in situ calibration approach was found to reduce the uncertainty between thermistors to about 0.05°C in a vineyard under arid conditions. In situ calibration results were similar to laboratory results before and after field deployment for temperatures ranging between 4 and 60°C. Thermistor offsets were found to change very little over a 5‐yr period, indicating that pre‐ or post‐laboratory calibration could be sufficient. The in situ approach can be useful when calibration prior to field deployment is unavailable and/or sensor failure prevents post‐field calibration.}, number={6}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={Kool, Dilia and Heitman, Joshua L. and Lazarovitch, Naftali and Agam, Nurit and Sauer, Thomas J. and Ben-Gal, Alon}, year={2016}, month={Nov}, pages={1514–1519} }
 @article{partitioning evaporation and transpiration in a maize field using heat-pulse sensors for evaporation measurement_2016, volume={59}, ISSN={2151-0032 2151-0040}, url={http://dx.doi.org/10.13031/trans.59.11059}, DOI={10.13031/trans.59.11059}, abstractNote={<abstract> . Evapotranspiration (ET) is the sum of soil water evaporation (E) and plant transpiration (T). E and T occur simultaneously in many systems with varying levels of importance, yet it is often very challenging to distinguish these fluxes separately in the field. Few studies have measured all three terms (ET, E, and T), and in the few cases where such measurements have been obtained, E is typically determined via destructive lysimetery. For 43 days in a fully developed maize ( L.) field, we continuously measured E using heat-pulse sensors and soil sensible heat balance, T using sap-flow gauges, and ET using an eddy covariance system. Crop evapotranspiration (ET<sub>c</sub>) was also calculated from the crop coefficient (K<sub>c</sub>) and the reference evapotranspiration (ET<sub>o</sub>), which was determined with the standardized Penman-Monteith equation. During the measurement period, E and T accounted for 13% and 87% of E+T, respectively. E responded to variations in soil moisture and net radiation, whereas T changed primarily with net radiation. All three ET estimation methods (individually measured E+T, eddy covariance ET, and crop ET<sub>c</sub>) demonstrated similar temporal trends and strong correlations (R<sup>2</sup> of 0.76 for ET<sub>c</sub> vs. E+T and 0.77 for ET vs. E+T), with the values of individually measured E+T close to crop ET<sub>c</sub> but larger than eddy covariance ET during the measurement period. Disparities in measurements were likely due to variations in measurement scale, which did not reflect the full range of field variability for individually measured E and T, and differences in response to declining soil moisture among the three approaches. Overall, the results support the need for individual measurement of each term (E, T, and ET) when attempting to interpret ET partitioning and suggest that soil heat-pulse sensors provide a viable complement to previously tested approaches for continuously determining E for ET partitioning during wetting-drying periods.}, number={2}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, year={2016}, month={Apr}, pages={591–599} }
 @article{kojima_heitman_flerchinger_ren_horton_2016, title={Sensible Heat Balance Estimates of Transient Soil Ice Contents}, volume={15}, ISSN={1539-1663}, url={http://dx.doi.org/10.2136/vzj2015.10.0134}, DOI={10.2136/vzj2015.10.0134}, abstractNote={Core Ideas Soil ice content is difficult to quantify. A sensible heat balance with heat pulse probes may indicate soil ice contents. A sensible heat balance can determine transient soil ice content from −5 to 0°C. Soil ice contents below −5°C can be determined with heat capacity changes. Heat pulse probes can monitor soil ice contents at and below 0°C. Soil ice content is an important component for winter soil hydrology. The sensible heat balance (SHB) method using measurements from heat pulse probes (HPPs) is a possible way to determine transient soil ice content. In a previous study, in situ soil ice content estimates with the SHB method were inaccurate, due to thermal conductivity errors and the use of relatively long time steps for calculations. The objective of this study is to reexamine the SHB method for soil ice content determination. A soil freezing and thawing laboratory experiment was performed with soil columns and heat exchangers. Transient soil ice contents in the soil columns during soil freezing and thawing were determined with the SHB method. The SHB method was able to determine dynamic changes in soil ice contents during initial freezing and final thawing for soil temperatures between −5 and 0°C when latent heat values associated with ice formation or with thawing were relatively large. During an extended freezing period, when soil temperatures were below −5°C, the small associated latent heat fluxes were below the sensitivity of the SHB method, and the SHB method did not provide accurate estimates of ice contents with time. However, the soil ice contents during the extended freezing period could be estimated well from changes in volumetric heat capacity ( C ) determined with HPP. Thus, combining the SHB method for initial freezing and final thawing, with a change in C method for extended freezing periods, allowed determination of dynamic soil ice contents for the entire range of freezing and thawing soil temperatures investigated. HPPs were able to measure soil ice contents.}, number={5}, journal={Vadose Zone Journal}, publisher={Wiley}, author={Kojima, Yuki and Heitman, Joshua L. and Flerchinger, Gerald N. and Ren, Tusheng and Horton, Robert}, year={2016}, month={May}, pages={vzj2015.10.0134} }
 @article{arya_heitman_2015, title={A Non-Empirical Method for Computing Pore Radii and Soil Water Characteristics from Particle-Size Distribution}, volume={79}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2015.04.0145}, abstractNote={Soil water characteristics (SWC) is a common requirement in studies of soil physics and hydrology, and modeling this property is preferred because experimental measurements are error-prone, time-consuming, and costly. However, unknown empirical parameters in SWC models remain a source of uncertainty. This study proposes a formulation for computing pore radii and SWCs from routinely available particle-size distribution (PSD), bulk density, and particle density data, without the need for incorporating unknown empirical parameters. The proposed model emerged from combining attributes of natural-packed soil structure with those of a counterpart hypothetical structure consisting of spherical particles, and has the form where rin is the pore radius for a given fraction of particles on the PSD curve, Φ is the porosity, wi is the fraction solid mass, ρb is the bulk density, ni is the number of spherical particles that can be formed using the fraction solid mass, and Ri is the mean particle radius for the fraction. The model was applied to calculate SWC for 41 soils consisting of loam, clay, sandy loam, and sand textures. Root mean square residuals (RMSRs) of log-transformed pressure heads were calculated to assess goodness of agreement between experimental pressure heads and those predicted by the non-empirical model of this study and the empirical model of Arya et al. The distribution of RMSR values (log10|h|, cm) showed a range from 0.021 to 1.309. When viewed in conjunction with plotted SWC curves, results showed reasonable to excellent agreement with experimental data in about 75% of the cases. Barring a few exceptions, predictions of the proposed model also agreed well with predictions of the empirical model of Arya et al.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Arya, Lalit M. and Heitman, Joshua L.}, year={2015}, pages={1537–1544} }
 @inproceedings{kays_mclaughlin_heitman_mohammadshirazi_brown_2015, title={Amending Soils for Enhanced Infiltration of Stormwater}, ISBN={9780784479025}, url={http://dx.doi.org/10.1061/9780784479025.012}, DOI={10.1061/9780784479025.012}, abstractNote={Rainfall events on urban compacted soils increase the volume and rate of stormwater runoff. A research study was conducted recently in North Carolina to investigate soil amendments to enhance infiltration into compacted soils. Sites were located in the coastal plain, piedmont, and mountain regions and the sites had sand, sandy clay, and sandy clay loam textured subsoils, respectively. The soil profiles were exhumed into the subsoils and compacted to simulate urban disturbed conditions. Physical treatments/amendments included compacted (control), shallow tillage (15 cm), and deep tillage (30 cm). Fertility amendments included agricultural lime and fertilizer according to soil test results. Triplicate plots were randomized on each of the sites. Fescue grass was seeded, mulched, and covered with jute matting. Steady state infiltration rate, bulk density, cone penetrometer, grass shoot biomass, and grass root biomass measurements were taken over the study period. Runoff from natural rainfall events was measured for twelve storm events at the two piedmont sites. Tillage greatly increased the infiltration rates and the effect remained after three years. There was evidence of some decline in infiltration rates at the mountain site, but none at the other sites, even though the bulk densities tended to increase over time at all sites. Doubling recommended lime rates, or adding compost, or water absorbing polyacrylamide usually had no effect on infiltration rates. The initial infiltration rates for compacted soils were usually < 1 cm hr -1 but the rates improved over several years to up to 10 cm hr -1 . This was somewhat surprising, but the trend was evident at all sites. The tilled soils had infiltration rates of 20 to 35 cm hr -1 at the end of at least two years. Because this far exceeds expected rainfall of 3 to 6 cm hr -1 for 2 to 10 year recurrence storms, the results suggest that treated areas may be able to accept significant amounts of runoff from impervious areas.}, booktitle={International Low Impact Development Conference 2015}, publisher={American Society of Civil Engineers}, author={Kays, Barrett L. and McLaughlin, Richard and Heitman, Joshua and Mohammadshirazi, Fatemeh and Brown, Virginia}, year={2015}, month={Jan} }
 @article{xiao_kuang_sauer_heitman_horton_2015, title={Bare Soil Carbon Dioxide Fluxes with Time and Depth Determined by High-Resolution Gradient-Based Measurements and Surface Chambers}, volume={79}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2015.02.0079}, abstractNote={Soil CO2 production rates and fluxes vary with time and depth. The shallow near-surface soil layer is important for myriad soil processes, yet knowledge of dynamic CO2 concentrations and fluxes in this complex zone is limited. We used a concentration gradient method (CGM) to determine CO2 production and effluxes with depth in shallow layers of a bare soil. The CO2 concentration was continuously measured at 13 depths in the 0- to 200-mm soil layer. For an 11-d period, 2% of the soil CO2 was produced below a depth of 175 mm, 8% was produced in the 50- to 175-mm soil layer, and 90% was produced in the 0- to 50-mm soil layer. Soil CO2 concentration showed similar diurnal patterns with temperature in deeper soil layers and out-of-phase diurnal patterns in surface soil layers. Soil CO2 flux from most of the soil layers can be described by an exponential function of soil temperature, with temperature sensitivity (Q10) ranging from 1.40 to 2.00 (1.62 ± 0.17). The temperature-normalized CO2 fluxes are related to soil water content with a positive linear relationship in surface soil layers and a negative relationship in deep soil layers. The CO2 fluxes from CGM and chamber methods had good agreement at multiple time scales, which showed that the CGM method was able to estimate near-surface soil CO2 fluxes and production. The contrasting patterns between surface and deep layers of soil CO2 concentration and fluxes suggest the necessity of intensive CO2 concentration measurements in the surface soil layer for accurate determination of soil-atmosphere CO2 flux when using the CGM.}, number={4}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Xiao, X. and Kuang, X. and Sauer, T. J. and Heitman, J. L. and Horton, R.}, year={2015}, pages={1073–1083} }
 @article{giese_wolf_velasco-cruz_roberts_heitman_2015, title={Cover Crop and Root Pruning Impacts on Vegetative Growth, Crop Yield Components, and Grape Composition of Cabernet Sauvignon}, volume={66}, ISSN={["1943-7749"]}, DOI={10.5344/ajev.2014.14100}, abstractNote={Complete vineyard floor cover cropping (inter- and intrarow) and vine root pruning were evaluated as tools to restrict vegetative growth of <i>Vitis vinifera</i> cv. Cabernet Sauvignon grapevines. Treatments were arranged in a split-plot, randomized, complete block design with cover crop schemes as main plots and annual vine root pruning (RP), or not (NRP), as subplots. Five perennial grasses as complete floor cover crops were compared to a more conventional under-trellis herbicide strip combined with KY-31 fescue interrows. KY-31 fescue and orchardgrass each reduced shoot growth rate by >30% in 2006 and >20% in 2007, below that of the herbicide-strip control vines. Root pruning independently reduced shoot growth rates. The combination of cover crop and RP decreased dormant pruning weights more than did the additive effects of either factor applied alone. Pruning weights in 2010 were reduced 8% below the control by RP, by 15% by cover crop, but by 38% when both treatments were applied. Leaf petiole N concentration at bloom was ~11% lower in RP vines in two of three years evaluated, but did not differ among vines grown with different cover crops. Stem water potential (Ψ<sub>stem</sub>) was not affected by treatments. Cover cropping did not reduce crop yield with the exception of reduced yield due to KY-31 fescue in 2006. Berry weights were slightly reduced by a RP × year interaction from 2007 to 2009 and by a year effect in 2011 compared to 2010. While complete vineyard floor cover cropping and root pruning were effective tools to reduce vine size and vigor, effects on canopy architecture and primary fruit chemistry were minimal and more influenced by seasonal variation.}, number={2}, journal={AMERICAN JOURNAL OF ENOLOGY AND VITICULTURE}, author={Giese, Gill and Wolf, Tony K. and Velasco-Cruz, Ciro and Roberts, Lucas and Heitman, Josh}, year={2015}, month={May}, pages={212–226} }
 @article{tian_heitman_horton_ren_2015, title={Determining Soil Ice Contents during Freezing and Thawing with Thermo-Time Domain Reflectometry}, volume={14}, ISSN={1539-1663}, url={http://dx.doi.org/10.2136/vzj2014.12.0179}, DOI={10.2136/vzj2014.12.0179}, abstractNote={Core Ideas An optimum heat application strategy was established for measuring thermal properties with the heat pulse method in partially frozen soils. At temperatures ≤ −5°C, T-TDR probes were able to measure soil ice content changes with acceptable accuracy. At temperatures between −5 and 0°C, soil ice contents could be estimated from water content before freezing, TDR measured unfrozen water content, and T-TDR measured total water content at temperatures below −5°C. Determining soil ice content during freezing and thawing is important and challenging for both engineering and environmental issues. The thermo-time domain reflectometry (T-TDR) probe, which can monitor unfrozen soil water content and soil thermal properties simultaneously, has the potential to measure ice content in partially frozen soils. The objective of this study was to identify an optimum heat application strategy for measuring soil thermal properties with T-TDR probes in partially frozen soil while minimizing ice melting during the process. The optimized heating schemes were then applied for monitoring soil ice content dynamics during freezing and thawing. The results indicated that the heat pulse method failed at temperatures between −5 and 0°C because of temperature field disturbances from latent heat of fusion. When soil temperatures were ≤ −5°C, ice melting during heat pulse applications could be limited effectively with a combination of 60-s heat-pulse duration and 450 J m−1 heating strength, or a 90-s heat-pulse duration and heating strength of 450 to 900 J m−1. With the optimized heating scheme, T-TDR probes were able to measure soil ice content changes at ≤ −5°C during freezing and thawing, and the errors were within ±0.05 m3 m−3 in sandy loams and within ±0.1 m3 m−3 in soils with high clay content. At temperatures between −5 and 0°C, soil ice contents could not be measured accurately with the heat-pulse method directly, but they could be estimated coarsely from water content before freezing, TDR measured unfrozen water content, and T-TDR measured total water content at temperatures below −5°C.}, number={8}, journal={Vadose Zone Journal}, publisher={Wiley}, author={Tian, Zhengchao and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2015}, month={Aug}, pages={vzj2014.12.0179} }
 @article{peng_heitman_horton_ren_2015, title={Field evaluation and improvement of the plate method for measuring soil heat flux density}, volume={214}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2015.09.001}, abstractNote={Soil heat flux is an important component of the energy balance at the land surface. Heat flux plates have been used widely to measure soil heat flux, but suffer from errors such as heat flow distortion and soil–plate contact resistance. The Philip correction and self-calibrating heat flux plates have been applied to minimize measurement errors. The objectives of this study were to evaluate the effectiveness of heat flux plate correction methods and to introduce improved approaches for applying these methods under field conditions. Soil heat flux at a depth (z) below the surface (Gz) was measured with conventional and self-calibrating plates buried at 2, 6, and 10 cm in a bare soil. Adjacent to the soil heat flux plates, soil thermal conductivity (λs) and temperature gradients were measured simultaneously with heat-pulse sensors, allowing Gz to be determined with the gradient method. The gradient method values were used as a standard to evaluate the performance of the heat flux plates. Temporal λs values were also estimated from soil sand content, bulk density and water content using a thermal conductivity model. At the 6- and 10-cm depths, the conventional plates underestimated Gz by 4.3–10.2 W m−2 due to heat flow distortion errors resulting from a mismatch between λs and plate thermal conductivity (λp). When the Philip correction was applied, both the measured and modeled λs values improved the accuracy of conventional heat flux plates. However, the modeling approach simplified the procedure for obtaining λs. The self-calibrating plate effectively corrected Gz errors associated with heat flow distortion (accurate to within 6.4 W m−2) at the 6 cm and 10 cm depths. At the 2 cm depth, both types of plates produced erroneous Gz data, which were attributed to alterations in the thermal field and heat flux pattern around the plates due to blocking convective heat and water transfer. We also demonstrated that the heating process of the self-calibrating plate could bias Gz data by disturbing the heat flow field around the plate. Voltage signals during and shortly after self-calibration should be discarded from data analysis. With these corrections, heat flux plates can provide an effective method for measuring soil heat flux.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Peng, Xiaoyang and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2015}, month={Dec}, pages={341–349} }
 @article{xiao_zhang_ren_horton_heitman_2015, title={Thermal Property Measurement Errors with Heat-Pulse Sensors Positioned near a Soil-Air Interface}, volume={79}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2014.12.0493n}, abstractNote={Heat‐pulse sensor measurements analyzed with pulsed infinite line source (PILS) theory have been widely used to measure soil properties. The PILS theory assumes that the measured soil medium is uniform and infinite. When the sensors are positioned near the soil surface, the effects of the heterogeneity associated with the soil–air interface should not be ignored. In 1999, Philip and Kluitenberg (PK99) proposed an analytical solution using an instantaneous heating model to analyze the effects of the soil–air interface on soil thermal property measurements with heat‐pulse sensors. The purpose of this study is to test the PK99 instantaneous heat source solution under controlled laboratory conditions. Soil thermal properties including volumetric heat capacity, thermal diffusivity, and thermal conductivity were measured with a commercially available dual‐needle heat‐pulse sensor buried at different depths beneath the soil surface. Three soil materials, sand, loamy sand, and sandy clay loam, were tested at both air‐dry and saturated moisture conditions. With shallow sensor burial, measured thermal properties were underestimated by up to 50%, similar to the predicted thermal properties from the PK99 analytical solution, due to the effects of the soil–air interface. Using PK99 to adjust thermal property values obtained from shallow sensors has potential to improve estimates of water content, evaporation, and other soil measurements derived from heat‐pulse sensors.}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Xiao, X. and Zhang, X. and Ren, T. and Horton, R. and Heitman, J. L.}, year={2015}, pages={766–771} }
 @article{kang_mclaughlin_amoozegar_heitman_duckworth_2015, title={Transport of dissolved polyacrylamide through a clay loam soil}, volume={243}, ISSN={["1872-6259"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84920432092&partnerID=MN8TOARS}, DOI={10.1016/j.geoderma.2014.12.022}, abstractNote={Polyacrylamide (PAM) is becoming a widely used soil conditioning and erosion control agent, and a better understanding of its transport is required to improve its use. In this study vertical PAM transport through a clay loam soil was investigated using thin soil columns (7.62-cm diameter × 2-cm thick) under saturated condition. The columns received a water-soluble, anionic PAM solution (16 Mg mol− 1 with 50 mol% charge density) under pulse and step (continuous) inputs using a constant-head method. The pulse input was 500 mg L− 1 PAM solution applied for 0.6 pore volume (PV), after which the input was switched to deionized (DI) water for 25 PVs. The step input was 25 mg L− 1 PAM solution applied continuously for 129 PVs. Saturated hydraulic conductivity (Ksat) was measured prior to PAM application and was monitored during PAM and DI water leaching. Leachate samples were collected frequently with time from each column and analyzed for the dissolved PAM concentration. The PAM applications reduced Ksat to 1% of the initial Ksat (4 cm h− 1) under the pulse input and to 0.3% of the initial Ksat under the step input. Transport of PAM was best-fitted with a two-region (dual-porosity) model. The fitted retardation factor (R) was more than two-fold greater for the step input (R = 2695) than for the pulse input (R = 1242). The results from transport modeling and pore size distribution analysis suggested that viscous PAM solution contributes to a mechanical entrapment of the PAM molecules, clogging most water-conducting pores smaller than 225–274 μm in diameter. Under saturated condition, either the pulse or step input of dissolved PAM could reduce seepage with limited mobility in the soil profile.}, journal={GEODERMA}, author={Kang, Jihoon and McLaughlin, Richard A. and Amoozegar, Aziz and Heitman, Joshua L. and Duckworth, Owen W.}, year={2015}, month={Apr}, pages={108–114} }
 @misc{kool_agam_lazarovitch_heitman_sauer_ben-gal_2014, title={A review of approaches for evapotranspiration partitioning}, volume={184}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2013.09.003}, abstractNote={Partitioning of evapotranspiration (ET) into evaporation from the soil (E) and transpiration through the stomata of plants (T) is challenging but important in order to assess biomass production and the allocation of increasingly scarce water resources. Generally, T is the desired component with the water being used to enhance plant productivity; whereas, E is considered a source of water loss or inefficiency. The magnitude of E is expected to be quite significant in sparsely vegetated systems, particularly in dry areas or in very wet systems such as surface irrigated crops and wetlands. In these cases, ET partitioning is fundamental to accurately monitor system hydrology and to improve water management practices. This paper aims to evaluate and summarize available methods currently used to separately determine E and T components. We presuppose that, to test the accuracy of ET partitioning methods (measurements and/or modeling), all three components, i.e., E, T and ET, must be estimated independently, but recognize that sometimes one of the components is taken as the residual of the other two. Models that were validated against measurements for their ability to partition between E and T are briefly discussed. To compare approaches, 52 ET partitioning studies were considered regarding estimates of the relative amount of E and for success of agreement in closing the ET = E + T equation. The E/ET ratio was found to exceed 30% in 32 of the studies, which confirms the hypothesis that E often constitutes a large fraction of ET and deserves independent consideration. Only 20 studies estimated E and T as well as ET, and had varied results. A number of studies succeeded to estimate E + T to within 10% of measured ET. Future challenges include development of models simulating the components of ET separately and advancement of methods for continuous measurement of E, T and/or the ratio between the two.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Kool, D. and Agam, N. and Lazarovitch, N. and Heitman, J. L. and Sauer, T. J. and Ben-Gal, A.}, year={2014}, month={Jan}, pages={56–70} }
 @article{davis_horton_heitman_ren_2014, title={An Experimental Study of Coupled Heat and Water Transfer in Wettable and Artificially Hydrophobized Soils}, volume={78}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2013.05.0182}, abstractNote={The effect of soil wettability on coupled heat and water transfer in soil is not well understood. The objective of this work was to determine the effect of soil wettability on coupled heat and water transfer for two wettable soils and their artificially hydrophobized counterparts. Closed soil cells instrumented with heat-pulse sensors provided in situ measurements of soil temperature, soil volumetric water content (θ), soil thermal conductivity (λ), and soil thermal diffusivity (α). Nonlinear temperature distributions developed in response to the 150°C m−1 temperature gradients applied to the soil cells for both the wettable and hydrophobized soils due to soil moisture redistribution. Hydrophobized sand and silt loam soils had different responses relative to their wettable counterparts. Soil moisture redistribution was similar in the wettable and hydrophobized sand soils. Net water transfer was reduced by 56% in the hydrophobized silt loam compared with the wettable silt loam. Reduced net water transfer in the hydrophobized silt loam indicated that water vapor transfer must have been lower in the hydrophobized silt loam than in the wettable silt loam. Diffusive pathways for water vapor may increase due to hydrophobicity. In both the wettable and hydrophobized soils, λ and α decreased in the warm regions and increased in the cold regions of the soil cells due to soil moisture redistribution. Wettability is a function of water content, and relative to wettable soil, water redistribution in hydrophobized soil is reduced only when the water content is small enough for the soil to behave as hydrophobic. If the water content is large enough for a hydrophobized soil to behave as wettable, water redistribution is similar to that in a wettable soil.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Davis, Dedrick D. and Horton, Robert and Heitman, Joshua L. and Ren, Tusheng}, year={2014}, pages={125–132} }
 @article{giese_velasco-cruz_roberts_heitman_wolf_2014, title={Complete vineyard floor cover crops favorably limit grapevine vegetative growth}, volume={170}, ISSN={["1879-1018"]}, DOI={10.1016/j.scienta.2014.03.011}, abstractNote={Complete vineyard floor cover crops were evaluated in a long-term study for their ability to regulate excessive vegetative growth of the grapevine (Vitis vinifera L.) variety ‘Cabernet Sauvignon’. Treatments were: tall fescue (Festuca arundinacea Shreb.) ‘KY-31′ and ‘Elite II’, hard fescue (Festuca ovina L.) ‘Aurora Gold’, perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), and an under-trellis herbicide strip combined with KY-31 fescue interrows. Compared to herbicide-treated soil strip, Elite II fescue reduced vine pruning weights (kg/vine) 28%, individual cane weight (g) 20%, and canopy leaf layer number 25%. KY-31 fescue produced the greatest biomass and stand density, while perennial ryegrass produced the least biomass and Aurora Gold hard fescue produced the lowest stand density. Elite II fescue produced less biomass but equivalent stand density compared to KY-31 fescue. Treatments minimally impacted vine water potential (Ψmd, Ψstem), indicating that the grasses were not overly competitive with grapevines for soil moisture. All grass treatments tended to depress grapevine nitrogen levels relative to the under-trellis herbicide strip treatment, but no treatment resulted in vine nitrogen levels below the acceptable sufficiency range. Because of its establishment and growth characteristics, desired suppression of vine vegetative growth, and its low impact on crop yield, we considered Elite II fescue the optimal cover crop evaluated.}, journal={SCIENTIA HORTICULTURAE}, author={Giese, Gill and Velasco-Cruz, Ciro and Roberts, Lucas and Heitman, Josh and Wolf, Tony K.}, year={2014}, month={May}, pages={256–266} }
 @article{kojima_heitman_flerchinger_ren_ewing_horton_2014, title={Field Test and Sensitivity Analysis of a Sensible Heat Balance Method to Determine Soil Ice Contents}, volume={13}, ISSN={1539-1663}, url={http://dx.doi.org/10.2136/vzj2014.04.0036}, DOI={10.2136/vzj2014.04.0036}, abstractNote={Soil ice content impacts winter vadose zone hydrology. It may be possible to estimate changes in soil ice content with a sensible heat balance (SHB) method, using measurements from heat pulse (HP) sensors. Feasibility of the SHB method is unknown because of difficulties in measuring soil thermal properties in partially frozen soils. The objectives of this study were (i) to examine the SHB method for determining in situ ice content, and (ii) to evaluate the required accuracy of HP sensors for use in the SHB method. Heat pulse sensors were installed in a bare field to measure soil temperatures and thermal properties during freezing and thawing events. In situ soil ice contents were determined at 60‐min intervals with SHB theory. Sensitivity of the SHB method to temperature, heat capacity, thermal conductivity, and time step size was analyzed based on numerically produced soil freezing and thawing events. The in situ ice contents determined with the SHB method were sometimes unrealistically large or even negative. Thermal conductivity accuracy and time step size were the key factors contributing to SHB errors, while temperature and heat capacity accuracy had less influence. Ice content estimated with a 15‐min SHB time step was more accurate than that estimated with a 60‐min time step. Sensitivity analysis indicated that measurement errors in soil temperature and thermal conductivity should be less than ±0.05°C and ±20%, respectively, but the error in the soil heat capacity could vary by ±50%. Thus, improving the accuracy of thermal conductivity measurements and using short time steps are required to accurately estimate soil ice contents with the SHB method.}, number={9}, journal={Vadose Zone Journal}, publisher={Wiley}, author={Kojima, Yuki and Heitman, Joshua L. and Flerchinger, Gerald N. and Ren, Tusheng and Ewing, Robert P. and Horton, Robert}, year={2014}, month={Sep}, pages={vzj2014.04.0036} }
 @article{kang_amoozegar_heitman_mclaughlin_2014, title={Granular and Dissolved Polyacrylamide Effects on Erosion and Runoff under Simulated Rainfall}, volume={43}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2014.01.0022}, abstractNote={Polyacrylamide (PAM) has been demonstrated to reduce erosion under many conditions, but less is known about the effects of its application method on erosion and concentrations in the runoff water. A rainfall simulation study was conducted to evaluate the performance of an excelsior erosion control blanket (cover) and two PAM application methods. The treatments were (i) no cover + no PAM (control), (ii) cover + no PAM, (iii) cover + granular PAM (GPAM), and (iv) cover + dissolved PAM (DPAM) applied to soil packed in wooden runoff boxes. The GPAM or DPAM (500 mg L−1) was surface-applied at a rate of 30 kg ha−1 1 d before rainfall simulation. Rainfall was applied at 83 mm h−1 for 50 min and then repeated for another 20 min after a 30-min rest period. Runoff samples were analyzed for volume, turbidity in nephelometric turbidity units (NTU), total suspended solids (TSS), sediment particle size distribution, and PAM concentration. The cover alone reduced turbidity and TSS in runoff by >60% compared with the control (2315 NTU, 2777 mg TSS L−1). The PAM further reduced turbidity and TSS by >30% regardless of the application method. The median particle diameter of eroded sediments for PAM treatments was seven to nine times that of the control (12.4 μm). Loss of applied PAM in the runoff water (not sediment) was 19% for the GPAM treatment but only 2% for the DPAM treatment. Both GPAM and DPAM were effective at improving groundcover performance, but DPAM resulted in much less PAM loss.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Kang, Jihoon and Amoozegar, Aziz and Heitman, Joshua L. and McLaughlin, Richard A.}, year={2014}, pages={1972–1979} }
 @article{fields_fonteno_jackson_heitman_owen_2014, title={Hydrophysical properties, moisture retention, and drainage profiles of wood and traditional components for greenhouse substrates}, volume={49}, number={6}, journal={HortScience}, author={Fields, J. S. and Fonteno, W. C. and Jackson, B. E. and Heitman, J. L. and Owen, J. S.}, year={2014}, pages={827–832} }
 @article{holland_howard_heitman_sauer_giese_sutton_agam_ben-gal_havlin_2014, title={Implications of Tall Fescue for Inter-Row Water Dynamics in a Vineyard}, volume={106}, ISSN={0002-1962}, url={http://dx.doi.org/10.2134/agronj13.0488}, DOI={10.2134/agronj13.0488}, abstractNote={Vineyards in the southeastern United States face challenges including poor internal soil drainage, high precipitation, and warm temperatures. This environment causes elevated humidity, creating ideal conditions for fungal diseases. Maintaining tall fescue ( Schedonorus arundinaceus Shreb) and resident vegetation ground cover in vineyard inter‐rows is a common cultural practice in the region, believed to benefit grape ( Vitis vinifera L.) production by increasing competition for soil water and thereby favorably reducing vine vegetative growth. We hypothesized that, although inter‐row fescue may reduce soil water availability, it may also increase humidity within the vineyard. Our objectives were to assess surface vapor flux from two inter‐row treatments (bare soil and tall fescue) and to determine any corresponding effects on soil water content and humidity within the inter‐row. Surface vapor flux, soil water content, and vapor pressure (30 cm height aboveground) were measured in inter‐rows subjected to each treatment. Observed surface vapor flux for fescue inter‐row exceeded that of bare soil by a daily average of 1.1 mm during the grape growing season. Despite fescue inter‐row evapotranspiration (ET), soil water depletion was insufficient to produce stress in the vines. Fescue inter‐row vapor pressure increased compared to bare soil inter‐rows by an average of 2% ( P < 0.09) during the growing season. Data suggest that fescue ET may increase inter‐row humidity in warm, humid environments, while providing only modest influence on soil water availability. Additional work including increased plot size to accommodate fetch for microclimate measurements, and biological assessment of humidity implications for disease is warranted.}, number={4}, journal={Agronomy Journal}, publisher={Wiley}, author={Holland, S. and Howard, A. and Heitman, J. L. and Sauer, T. J. and Giese, W. and Sutton, T. B. and Agam, N. and Ben-Gal, A. and Havlin, J.}, year={2014}, month={Jul}, pages={1267–1274} }
 @article{deol_heitman_amoozegar_ren_horton_2014, title={Inception and Magnitude of Subsurface Evaporation for a Bare Soil with Natural Surface Boundary Conditions}, volume={78}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2013.12.0520}, abstractNote={A dry surface layer (DSL) forms when wet soil is exposed to the sun; development of a DSL coincides with a shift between surface and subsurface evaporation. There remains debate as to when this shift from surface to subsurface evaporation occurs relative to the timing of the shift between potential and falling‐rate evaporation. We performed a field experiment to investigate the onset of subsurface evaporation, development of the DSL, and the extent of the evaporation zone. Our objective was to determine the timing of the onset of subsurface evaporation with respect to decline in evaporation rates. We estimated total (surface plus subsurface) and subsurface soil evaporation rates using microlysimeter (water mass balance) and sensible heat balance (SHB) approaches, respectively, for a bare loamy sand soil under natural wetting and drying cycles. Results showed that the onset of subsurface evaporation coincided with the beginning of falling‐rate evaporation. The evaporation zone extended into the subsurface when evaporation rates fell below the potential rate but were still as high as 50% of potential evaporation. Over a 5‐d drying event, estimated evaporation zones were as deep as 4 to 9 mm, and the estimated DSL had a maximum depth of approximately 6 mm. A low soil water content‐dependent albedo was observed when evaporation occurred at potential rates, but albedo increased as evaporation rates declined. Data from the intensive observation period suggest that this increase in albedo corresponded to formation of a DSL and onset of subsurface evaporation. Overall, surface drying and formation of a DSL appeared to be a dominant process for this coarse‐texture soil exposed to ambient boundary conditions, even as evaporation rates remained relatively high (0.3 mm h −1 ).}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Deol, Pukhraj K. and Heitman, Joshua L. and Amoozegar, Aziz and Ren, Tusheng and Horton, Robert}, year={2014}, pages={1544–1551} }
 @article{zhang_heitman_horton_ren_2014, title={Measuring Near-Surface Soil Thermal Properties with the Heat-Pulse Method: Correction of Ambient Temperature and Soil-Air Interface Effects}, volume={78}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2014.01.0014}, abstractNote={Large temperature gradients and proximity to the soil–air interface affect the measurement accuracy of thermal properties with the heat‐pulse probe (HPP). The objective of this study is to improve the HPP methodology for measuring soil heat capacity ( C ) and thermal conductivity (λ) in the surface soil layer by reducing the effects of ambient temperature variation and the soil–air interface. Thermal properties of eight soil layers (0–6, 2–6, 6–12, 12–18, 18–24, 24–30, 30–36, and 36–42 mm) were measured with the HPP in a loamy sand soil in two experiments with varying moisture conditions. Results were compared with values estimated with the de Vries models. Temperature drift caused by natural warming and cooling was removed from the observed trend of ambient temperature change with time. The influence of the soil–air interface was taken into account with a new solution using pulsed infinite line source theory with adiabatic boundary conditions. When ambient temperature change was considered, the HPP were capable of providing reasonable thermal property results at soil depths greater than 6 mm. For the 0‐ to 6‐mm depth layer, the HPP signals were affected simultaneously by ambient temperature drift and the soil‐air interface, and mixed scenarios were produced. Around midday, the HPP temperature by time curves were distorted so seriously that the effect of ambient temperature drift could not be removed. At other times, large errors were observed in the estimated C and λ data, even when ambient temperature drift was removed. When the effect of the soil–air interface was accounted for, however, C and λ measurement accuracies in the 0‐ to 6‐mm layer were improved significantly. The RMSE of C was reduced from 0.43 MJ m −3 °C −1 to 0.29 MJ m −3 °C −1 in Exp. 1, and from 0.52 MJ m −3 °C −1 to 0.34 MJ m −3 °C −1 in Exp. 2. Significant error reduction was also observed in λ measurements. Thus, to obtain accurate field measurements of shallow soil thermal properties, the ambient temperature drift and the impact of the soil–air interface must be properly taken into account.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Zhang, Xiao and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2014}, pages={1575–1583} }
 @article{xiao_heitman_sauer_ren_horton_2014, title={Sensible Heat Balance Measurements of Soil Water Evaporation beneath a Maize Canopy}, volume={78}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2013.08.0371}, abstractNote={Soil water evaporation is an important component of the water budget in cropped fields; few methods are available for continuous and independent measurement. A sensible heat balance (SHB) approach has been demonstrated for continuously determining soil water evaporation under bare surface conditions. Applicability of SHB measurements beneath a crop canopy cover has not been evaluated. We tested SHB using heat-pulse sensors to estimate evaporation beneath a full maize (Zea mays L.) canopy. We also implemented a modified SHB approach incorporating below-canopy net radiation, which extended the range of conditions under which SHB is applicable. Evaporation was measured at three positions: row (R), interrow (I), and interrow with roots excluded (IE). Evaporation rates were generally small, averaging <0.7 mm d−1 across all dates, positions, and measurement methods during the drying period. The SHB evaporation estimates varied among R, I, and IE, with cumulative totals of 4.4, 7.4, and 7.9 mm, respectively, during a 12-d drying period. Lower soil water contents from plant water uptake reduced evaporation rates at R more appreciably with time than at the other positions; I and IE provided similar evaporation patterns. The SHB evaporation estimates at R and I were compared with microlysimeter data on 8 d. Correlation between approaches was modest (r2 = 0.61) but significant (p < 0.001) when compared separately at R and I positions. Correlation was improved (r2 = 0.81) when evaporation estimates were combined across positions, with differences between SHB and microlysimeters typically within the range of values obtained from microlysimeter replicates. Overall, the results suggest good potential for using SHB and modified SHB approaches to determine soil water evaporation in a cropped field. The SHB approach allowed continuous daily estimates of evaporation, separate from evapotranspiration and without destructive sampling.}, number={2}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Xiao, X. and Heitman, J. L. and Sauer, T. J. and Ren, T. and Horton, R.}, year={2014}, pages={361–368} }
 @article{duckworth_heitman_polizzotto_2014, title={Soil Water: From Molecular Structure to Behavior}, volume={5}, number={1}, journal={Nature Education}, author={Duckworth, O.W. and Heitman, J.L. and Polizzotto, M.L.}, year={2014} }
 @article{kool_ben-gal_agam_simunek_heitman_sauer_lazarovitch_2014, title={Spatial and diurnal below canopy evaporation in a desert vineyard: Measurements and modeling}, volume={50}, ISSN={["1944-7973"]}, DOI={10.1002/2014wr015409}, abstractNote={Abstract Evaporation from the soil surface ( E ) can be a significant source of water loss in arid areas. In sparsely vegetated systems, E is expected to be a function of soil, climate, irrigation regime, precipitation patterns, and plant canopy development and will therefore change dynamically at both daily and seasonal time scales. The objectives of this research were to quantify E in an isolated, drip‐irrigated vineyard in an arid environment and to simulate below canopy E using the HYDRUS (2‐D/3‐D) model. Specific focus was on variations of E both temporally and spatially across the inter‐row. Continuous above canopy measurements, made in a commercial vineyard, included evapotranspiration, solar radiation, air temperature and humidity, and wind speed and direction. Short‐term intensive measurements below the canopy included actual and potential E and solar radiation along transects between adjacent vine‐rows. Potential and actual E below the canopy were highly variable, both diurnally and with distance from the vine‐row, as a result of shading and distinct wetted areas typical to drip irrigation. While the magnitude of actual E was mostly determined by soil water content, diurnal patterns depended strongly on position relative to the vine‐row due to variable shading patterns. HYDRUS (2‐D/3‐D) successfully simulated the magnitude, diurnal patterns, and spatial distribution of E , including expected deviations as a result of variability in soil saturated hydraulic conductivity.}, number={8}, journal={WATER RESOURCES RESEARCH}, author={Kool, D. and Ben-Gal, A. and Agam, N. and Simunek, J. and Heitman, J. L. and Sauer, T. J. and Lazarovitch, N.}, year={2014}, month={Aug}, pages={7035–7049} }
 @article{haynes_mclaughlin_heitman_2013, title={Comparison of Methods to Remediate Compacted Soils for Infiltration and Vegetative Establishment}, volume={03}, ISSN={2162-5360 2162-5379}, url={http://dx.doi.org/10.4236/ojss.2013.35027}, DOI={10.4236/ojss.2013.35027}, abstractNote={The process of constructing roads and buildings usually involves the removal of topsoil and grading of the subsoil followed by a variety of activities using heavy equipment. This presents multiple challenges in attempts to establish vegetation on these areas: low nutrient soils with little organic matter, high bulk densities, and low infiltration rates. The goals of this preliminary study were to quantify the impacts of soil compaction remediation methods on infiltration, runoff water quality, and vegetation establishment. The objectives were to measure: 1) steady state infiltration rate (IR); 2) quantity and quality of storm water runoff; and 3) ground cover, biomass production, and rooting depth of vegetation during early establishment. We evaluated four treatments: a compacted soil (C), a compacted soil with core aeration (A), a compacted soil with deep (20 - 30 cm) tillage (DT), and a compacted soil with deep tillage and incorporated compost (CT). Sites 1 and 2 received C, A and DT treatments and Site 3 received only DT and CT treatments. At Site 1, runoff from natural rainfall events was collected in plastic tubs at the bottom of each 2 × 1 m plot, and samples were measured for volume and sediment. Infiltration rates were determined using a Cornell Sprinkle Infiltrometer at all three sites. At Site 1, the A treatment had a higher erosion rate during two of four rain events and higher runoff volume during three of four rain events, when compared to C and DT. However, the aerator was only able to penetrate 1 - 2 cm due to the compacted soil. Average event runoff ranged from 0 to 22% (0 - 9.3 mm), 10 to 60% (1.9 - 26.2 mm), and 0 to 3.5% (0 - 1.1 mm) of the total rainfall for C, A, and DT, respectively. There was no difference between C and A for vegetative biomass and IR, but both biomass and IR were greater in the DT plots. Treatment DT had an average IR of 15 cm·hr-1, compared to 0.16 and 0.21 cm·hr-1 for C and A, respectively. Roots were much more abundant at the 20 - 50 cm depths with DT. At Site 2, there were no significant differences in IR, with many values too low to be measured with the infiltrometer. Vegetative cover also did not differ between the three treatments due to poor (16% - 22% cover) grass establishment. Infiltration rates at Site 3 were measured immediately after tillage and were 10× those at Site 2, measured 2 months after tillage, but DT and CT values were not different. The results suggest that deep tillage prior to seeding could maximize long-term vegetation growth and provide areas of high infiltration to minimize post-construction stormwater discharges, as long as vigorous vegetation can be established quickly.}, number={05}, journal={Open Journal of Soil Science}, publisher={Scientific Research Publishing, Inc.}, author={Haynes, Matthew A. and McLaughlin, Richard A. and Heitman, Joshua L.}, year={2013}, pages={225–234} }
 @article{meijer_heitman_white_austin_2013, title={Measuring erosion in long-term tillage plots using ground-based lidar}, volume={126}, ISSN={0167-1987}, url={http://dx.doi.org/10.1016/j.still.2012.07.002}, DOI={10.1016/j.still.2012.07.002}, abstractNote={Erosion remains a serious problem for agricultural soils throughout the world. Tillage significantly affects a soil's susceptibility to erosion. Erosion research is usually conducted in situ by capturing eroded sediment in brief, natural or artificial rainfall events. Methods for measuring long-term erosion are needed to better understand long-term effects of soil management. Landscape change resulting from erosion may be accurately characterized using ground-based lidar. Ground-based lidar data were collected in 2010 at a long-term (28-yr) trial of nine tillage treatments in the North Carolina Piedmont. Tillage effects on plot-surface elevations were examined after removing large-scale variation in elevation (slope) by detrending with first- through fourth-order polynomials. Residuals represented the elevation difference from the trend for each location. Mean plot elevations were calculated for datasets from each detrending model and used to assess erosion. In the subsequent elevation analysis, data derived from the second-order polynomial had the highest R2, attributing 66% of the variation in elevation to block and treatment. Treatment elevations relative to no-till (NT) ranged from +3.20 cm in the fall chisel (CHfa) plots to −13.28 cm in the fall moldboard plow plus disk treatment. Weeds in lesser-tilled treatments such as CHfa and no-till plus in-row subsoiling resulted in artificially high elevation measurements. In general, the most intensely-tilled treatments had the lowest elevations and the least-tilled treatments had the highest. NT was used as the reference elevation for no change, and soil loss was calculated using these data along with field-collected estimates of bulk density. The relative elevation differences corresponded to a maximum soil loss of 1891 Mg ha−1, which corresponds to an average annual soil loss of 67.5 Mg ha−1 yr−1. Soil loss estimates were similar to others estimated from soil profile truncation. This research indicates that ground-based lidar data can be used to estimate soil elevation changes and thus soil loss due to tillage-induced erosion.}, journal={Soil and Tillage Research}, publisher={Elsevier BV}, author={Meijer, A.D. and Heitman, J.L. and White, J.G. and Austin, R.E.}, year={2013}, month={Jan}, pages={1–10} }
 @article{holland_heitman_howard_sauer_giese_ben-gal_agam_kool_havlin_2013, title={Micro-Bowen ratio system for measuring evapotranspiration in a vineyard interrow}, volume={177}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2013.04.009}, abstractNote={Sparse canopy systems such as vineyards are comprised of multiple components (e.g., vines, interrow soil and/or groundcover) that each contribute to system water and energy balance. Understanding component water and energy fluxes is critical for informing management decisions aimed at improving productivity and water use efficiency. Few methods are available to accurately and continuously measure component fluxes. We tested a novel micro-Bowen ratio (MBR) energy balance system for determining interrow evapotranspiration (ET) flux within a vineyard. Our objectives were to develop MBR methodology to measure ET flux from the vineyard interrow and to compare MBR ET measurements for bare soil and fescue interrow conditions to independent ET estimates. MBR methodology utilized measurement of air temperature and water vapor concentration at 1 and 6 cm heights within 2.7 m wide interrows. Measured ET rates were well correlated between MBR systems and micro-lysimeters for both fescue (R2 = 0.99) and bare surface (R2 = 0.89) interrow conditions, though MBR ET rates were larger than those determined from micro-lysimeters in both cases (20 and 60%, respectively). MBR daily ET estimates, determined by compositing measurements from fescue interrows and bare soil under vines, were also well correlated to (R2 = 0.70) and of similar magnitude as vineyard eddy covariance ET measurements during periods when the vines were dormant. Overall, MBR systems appeared to provide a reasonable approach to determine ET for the interrow component within the vineyard. Similar methodology may be useful to better understand components’ contributions to water and energy fluxes in other complex or sparse canopy systems.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Holland, S. and Heitman, J. L. and Howard, A. and Sauer, T. J. and Giese, W. and Ben-Gal, A. and Agam, N. and Kool, D. and Havlin, J.}, year={2013}, month={Aug}, pages={93–100} }
 @article{kojima_heitman_flerchinger_horton_2013, title={Numerical Evaluation of a Sensible Heat Balance Method to Determine Rates of Soil Freezing and Thawing}, volume={12}, ISSN={1539-1663}, url={http://dx.doi.org/10.2136/vzj2012.0053}, DOI={10.2136/vzj2012.0053}, abstractNote={In situ determination of soil freezing and thawing is difficult despite its importance for many environmental processes. A sensible heat balance (SHB) method using a sequence of heat pulse probes has been shown to accurately measure water evaporation in subsurface soil, and it has the potential to measure soil freezing and thawing. Determination of soil freezing and thawing may be more challenging than evaporation, however, because the latent heat of fusion is smaller than the latent heat of vaporization. Furthermore, convective heat flow associated with liquid water flow and occurrence of evaporation or condensation during freezing and thawing may cause inaccurate estimation of freezing and thawing with the SHB method. The objective of this study was to examine the applicability of the SHB concept to soil freezing and thawing. Soil freezing and thawing events were simulated with the simultaneous heat and water (SHAW) model. Ice contents were estimated by applying the SHB concept to numerical data produced by the SHAW model. Close agreement between the SHB‐estimated and the SHAW‐simulated ice contents were observed at depths below 24 mm. The main cause of inaccuracies with the SHB method was poor estimation of heat conduction at the 12‐mm depth, possibly due to simplifications of temporal or vertical distributions of temperature and thermal conductivity. The effects of convective heat flow and concurrent evaporation or condensation and freezing or thawing on the SHB method were small. The results indicate that the SHB method is conceptually suitable for estimating soil freezing and thawing. Independent, accurate estimates of thermal properties must be available to effectively use the SHB method to determine in situ soil freezing and thawing.}, number={1}, journal={Vadose Zone Journal}, publisher={Wiley}, author={Kojima, Yuki and Heitman, Joshua L. and Flerchinger, Gerald N. and Horton, Robert}, year={2013}, month={Feb}, pages={vzj2012.0053} }
 @book{mclaughlin_amoozegar_duckworth_heitman_2013, place={Raleigh}, title={Optimizing Soil-Polyacrylamide Interactions for Erosion Control at Construction Sites}, number={12-06-W.}, institution={NC Water Resources Research Institute}, author={McLaughlin, R. and Amoozegar, A. and Duckworth, O. and Heitman, J.}, year={2013} }
 @article{matthews_fiscus_smith_heitman_2013, title={Quantifying Plant Age and Available Water Effects on Soybean Leaf Conductance}, volume={105}, ISSN={0002-1962}, url={http://dx.doi.org/10.2134/agronj2012.0263}, DOI={10.2134/agronj2012.0263}, abstractNote={Given the ever‐present threat of drought and the knowledge that water availability is the strongest limiting factor in vegetation growth, it is important to characterize the effect of water limitations on agricultural production. In this study, a small field plot technique for controlling soil moisture content suitable for physiological research in moist, humid areas was tested. We characterized the effect of water stress on total leaf conductance ( g l ) for two distinct determinate soybean [ Glycine max (L.) Merr.] genotypes. Based on these findings, a model of g l as a function of plant age and soil moisture content was formulated and validated. The dependency of g l on plant age was well represented by a parabolic function that increased throughout the vegetative period, peaked around anthesis, and decreased throughout the reproductive period and senescence. A sigmoidal function explained the relation of g l to plant‐available soil water content. This new empirical model effectively quantifies the response of g l to plant‐available soil water and plant age with a functional form similar to the abscisic acid related Tardieu–Davies model.}, number={1}, journal={Agronomy Journal}, publisher={Wiley}, author={Matthews, Jessica L. and Fiscus, Edwin L. and Smith, Ralph C. and Heitman, Joshua L.}, year={2013}, month={Jan}, pages={28–36} }
 @article{kang_sowers_duckworth_amoozegar_heitman_mclaughlin_2013, title={Turbidimetric Determination of Anionic Polyacrylamide in Low Carbon Soil Extracts}, volume={42}, ISSN={["1537-2537"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84887582502&partnerID=MN8TOARS}, DOI={10.2134/jeq2013.07.0279}, abstractNote={Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM–hyamine complex. The PAM calibration curve with DI water showed a strong linear relationship (r2 = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L−1. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship (r2 > 0.97) and lowest detection limit (0.3 to 1.2 mg L−1), compared with those of the lower charge density PAMs (0.7 to 23 mg L−1). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Kang, Jihoon and Sowers, Tyler D. and Duckworth, Owen W. and Amoozegar, Aziz and Heitman, Joshua L. and McLaughlin, Richard A.}, year={2013}, pages={1902–1907} }
 @article{pan_boyles_white_heitman_2012, title={Characterizing Soil Physical Properties for Soil Moisture Monitoring with the North Carolina Environment and Climate Observing Network}, volume={29}, ISSN={["0739-0572"]}, DOI={10.1175/jtech-d-11-00104.1}, abstractNote={Abstract Soil moisture has important implications for meteorology, climatology, hydrology, and agriculture. This has led to growing interest in development of in situ soil moisture monitoring networks. Measurement interpretation is severely limited without soil property data. In North Carolina, soil moisture has been monitored since 1999 as a routine parameter in the statewide Environment and Climate Observing Network (ECONet), but with little soils information available for ECONet sites. The objective of this paper is to provide soils data for ECONet development. The authors studied soil physical properties at 27 ECONet sites and generated a database with 13 soil physical parameters, including sand, silt, and clay contents; bulk density; total porosity; saturated hydraulic conductivity; air-dried water content; and water retention at six pressures. Soil properties were highly variable among individual ECONet sites [coefficients of variation (CVs) ranging from 12% to 80%]. This wide range of properties suggests very different behavior among sites with respect to soil moisture. A principal component analysis indicated parameter groupings associated primarily with soil texture, bulk density, and air-dried water content accounted for 80% of the total variance in the dataset. These results suggested that a few specific soil properties could be measured to provide an understanding of differences in sites with respect to major soil properties. The authors also illustrate how the measured soil properties have been used to develop new soil moisture products and data screening for the North Carolina ECONet. The methods, analysis, and results presented here have applications to North Carolina and for other regions with heterogeneous soils where soil moisture monitoring is valuable.}, number={7}, journal={JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY}, publisher={American Meteorological Society}, author={Pan, Weinan and Boyles, R. P. and White, J. G. and Heitman, J. L.}, year={2012}, month={Jul}, pages={933–943} }
 @article{long_heitman_tobias_philips_song_2012, title={Co-Occurring Anammox, Denitrification, and Codenitrification in Agricultural Soils}, volume={79}, ISSN={0099-2240 1098-5336}, url={http://dx.doi.org/10.1128/AEM.02520-12}, DOI={10.1128/aem.02520-12}, abstractNote={ABSTRACT Anammox and denitrification mediated by bacteria are known to be the major microbial processes converting fixed N to N 2 gas in various ecosystems. Codenitrification and denitrification by fungi are additional pathways producing N 2 in soils. However, fungal codenitrification and denitrification have not been well investigated in agricultural soils. To evaluate bacterial and fungal processes contributing to N 2 production, molecular and 15 N isotope analyses were conducted with soil samples collected at six different agricultural fields in the United States. Denitrifying and anammox bacterial abundances were measured based on quantitative PCR (qPCR) of nitrous oxide reductase ( nosZ ) and hydrazine oxidase ( hzo ) genes, respectively, while the internal transcribed spacer (ITS) of Fusarium oxysporum was quantified to estimate the abundance of codenitrifying and denitrifying fungi. 15 N tracer incubation experiments with 15 NO 3 − or 15 NH 4 + addition were conducted to measure the N 2 production rates from anammox, denitrification, and codenitrification. Soil incubation experiments with antibiotic treatments were also used to differentiate between fungal and bacterial N 2 production rates in soil samples. Denitrifying bacteria were found to be the most abundant, followed by F. oxysporum based on the qPCR assays. The potential denitrification rates by bacteria and fungi ranged from 4.118 to 42.121 nmol N 2 -N g −1 day −1 , while the combined potential rates of anammox and codenitrification ranged from 2.796 to 147.711 nmol N 2 -N g −1 day −1 . Soil incubation experiments with antibiotics indicated that fungal codenitrification was the primary process contributing to N 2 production in the North Carolina soil. This study clearly demonstrates the importance of fungal processes in the agricultural N cycle.}, number={1}, journal={Applied and Environmental Microbiology}, publisher={American Society for Microbiology}, author={Long, Andrew and Heitman, Joshua and Tobias, Craig and Philips, Rebecca and Song, Bongkeun}, year={2012}, month={Oct}, pages={168–176} }
 @article{spence_osmond_childres_heitman_robarge_2012, title={Effects of Lawn Maintenance on Nutrient Losses Via Overland Flow During Natural Rainfall Events}, volume={48}, ISSN={1093-474X}, url={http://dx.doi.org/10.1111/j.1752-1688.2012.00658.x}, DOI={10.1111/j.1752-1688.2012.00658.x}, abstractNote={Spence, Porchè L., Deanna L. Osmond, Wesley Childres, Joshua L. Heitman, and Wayne P. Robarge, 2012. Effects of Lawn Maintenance on Nutrient Losses Via Overland Flow During Natural Rainfall Events. Journal of the American Water Resources Association (JAWRA) 48(5): 909‐924. DOI: 10.1111/j.1752‐1688.2012.00658.x Abstract: A sampling system was used to evaluate the effect of residential lawn management on nutrient losses via overland flow generated during natural rainfall events from three residential landscapes: a high maintenance fescue lawn (HMFL), a low maintenance fescue lawn (LMFL), and a mixed forested residential landscape (FRL). A sampling system was located in designated areas within each landscape such that 100% of the runoff follows natural flow paths to the outlet ports and collects in sterile Nalgene ® B 3 media bags (Thermo Fisher Scientific, Rochester, NY). A rainfall event was defined as producing ≥2.54 mm of water. A total of 87 rainfall events occurred during a 20‐month monitoring period. The total runoff volume collected from the LMFL was higher than from the HMFL and FRL, but on average <1% of the total rainfall was collected from the three landscapes. Mean nitrate concentrations from each lawn did not exceed 0.6 mg N/l. Nutrient unit area losses from the HMFL, LMFL, and FRL were 1,000 times less than fertilizer and throughfall inputs, which were due to the presence of well‐structured soils (low bulk densities) with high infiltration rates. This study demonstrated that the frequency of runoff, total runoff volumes, and nutrient losses during natural rainfall events are lower from highly maintained (i.e., irrigation, fertilizer application, and reseeding) densely uniform manicured lawns than low maintenance lawns and forested residential landscapes.}, number={5}, journal={JAWRA Journal of the American Water Resources Association}, publisher={Wiley}, author={Spence, Porchè L. and Osmond, Deanna L. and Childres, Wesley and Heitman, Joshua L. and Robarge, Wayne P.}, year={2012}, month={May}, pages={909–924} }
 @book{meijer_walters_white_heitman_howard_2012, title={Long-term Tillage Effects on Corn and Soybean Yield in the Piedmont}, number={AG 439 80}, journal={SoilFact}, institution={NC Cooperative Extension}, author={Meijer, A. and Walters, R.D. and White, J.G. and Heitman, J.L. and Howard, A.}, year={2012} }
 @article{xiao_lu_heitman_horton_ren_2012, title={Measuring Subsurface Soil-Water Evaporation with an Improved Heat-Pulse Probe}, volume={76}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj2011.0052n}, abstractNote={Recently a three‐needle heat‐pulse probe has been used to monitor subsurface soil‐water evaporation dynamics. Several of these probes have to be installed precisely at different depths to measure subsurface evaporation for multiple soil layers, and approximation of the shallow temperature gradient is limited by needle spacing. In this study, an 11‐needle heat‐pulse probe, including four heating needles among the 11 temperature needles and 1‐mm spacing between the upper‐most needles, is used to determine soil‐water evaporation in the 0‐ to 5‐cm soil layer. A field test showed that 4 d after irrigation, evaporation was observed in the 1.5‐ to 4‐ and 4‐ to 10‐mm soil layers and that the peak evaporation rate in the 1.5‐ to 4‐ and 4‐ to 10‐mm soil layer were 0.26 and 0.18 mm h −1 , respectively. After 5 d, the bottom of the evaporation zone propagated to a depth of 17 mm, and the peak evaporation rate in the 10‐ to 17‐mm soil layer reached 0.15 mm h −1 . After 6 d, there was significant evaporation occurring in the 17‐ to 23‐ mm soil layer with a peak evaporation rate of 0.15 mm h −1 . The new 11‐needle heat‐pulse probe was better able to measure the depth and time dynamics of subsurface soil water evaporation for multiple soil layers by improving on the previous three‐needle design.}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Xiao, Zhang and Lu, Sen and Heitman, Joshua and Horton, Robert and Ren, Tusheng}, year={2012}, pages={876–879} }
 @article{deol_heitman_amoozegar_ren_horton_2012, title={Quantifying nonisothermal subsurface soil water evaporation}, volume={48}, ISSN={0043-1397}, url={http://dx.doi.org/10.1029/2012WR012516}, DOI={10.1029/2012wr012516}, abstractNote={[1] Accurate quantification of energy and mass transfer during soil water evaporation is critical for improving understanding of the hydrologic cycle and for many environmental, agricultural, and engineering applications. Drying of soil under radiation boundary conditions results in formation of a dry surface layer (DSL), which is accompanied by a shift in the position of the latent heat sink from the surface to the subsurface. Detailed investigation of evaporative dynamics within this active near-surface zone has mostly been limited to modeling, with few measurements available to test models. Soil column studies were conducted to quantify nonisothermal subsurface evaporation profiles using a sensible heat balance (SHB) approach. Eleven-needle heat pulse probes were used to measure soil temperature and thermal property distributions at the millimeter scale in the near-surface soil. Depth-integrated SHB evaporation rates were compared with mass balance evaporation estimates under controlled laboratory conditions. The results show that the SHB method effectively measured total subsurface evaporation rates with only 0.01–0.03 mm h−1difference from mass balance estimates. The SHB approach also quantified millimeter-scale nonisothermal subsurface evaporation profiles over a drying event, which has not been previously possible. Thickness of the DSL was also examined using measured soil thermal conductivity distributions near the drying surface. Estimates of the DSL thickness were consistent with observed evaporation profile distributions from SHB. Estimated thickness of the DSL was further used to compute diffusive vapor flux. The diffusive vapor flux also closely matched both mass balance evaporation rates and subsurface evaporation rates estimated from SHB.}, number={11}, journal={Water Resources Research}, publisher={American Geophysical Union (AGU)}, author={Deol, Pukhraj and Heitman, Josh and Amoozegar, Aziz and Ren, Tusheng and Horton, Robert}, year={2012}, month={Nov} }
 @article{taggart_heitman_shi_vepraskas_2012, title={Temperature and Water Content Effects on Carbon Mineralization for Sapric Soil Material}, volume={32}, ISSN={0277-5212 1943-6246}, url={http://dx.doi.org/10.1007/S13157-012-0327-3}, DOI={10.1007/S13157-012-0327-3}, number={5}, journal={Wetlands}, publisher={Springer Science and Business Media LLC}, author={Taggart, Matthew and Heitman, J. L. and Shi, Wei and Vepraskas, Michael}, year={2012}, month={Jul}, pages={939–944} }
 @inbook{heitman_horton_2011, title={Coupled Heat and Water Transfer in Soil}, ISBN={9789048135844 9789048135851}, ISSN={1388-4360 1871-756X}, url={http://dx.doi.org/10.1007/978-90-481-3585-1_33}, DOI={10.1007/978-90-481-3585-1_33}, booktitle={Encyclopedia of Agrophysics}, publisher={Springer Netherlands}, author={Heitman, Joshua L. and Horton, Robert}, year={2011}, pages={155–162} }
 @article{xiao_horton_sauer_heitman_ren_2011, title={Cumulative Soil Water Evaporation as a Function of Depth and Time}, volume={10}, ISSN={["1539-1663"]}, DOI={10.2136/vzj2010.0070}, abstractNote={Soil water evaporation is an important component of the surface water balance and the surface energy balance. Accurate and dynamic measurements of soil water evaporation enhance the understanding of water and energy partitioning at the land–atmosphere interface. The objective of this study was to measure the cumulative soil water evaporation with time and depth in a bare field. Cumulative water evaporation at the soil surface was measured by the Bowen ratio method. Subsurface cumulative soil water evaporation was determined with the heat pulse method at fine-scale depth increments. Following rainfall, the subsurface cumulative evaporation curves followed a pattern similar to the surface cumulative evaporation curve, with approximately a 2-d lag before evaporation was indicated at the 3- and 9-mm soil depths, and several more days' delay in deeper soil layers. For a 21-d period in 2007, the cumulative evaporation totals at soil depths of 0, 3, 9, 15, and 21 mm were 60, 44, 29, 13, and 8 mm, respectively. For a 16-d period in 2008, the cumulative evaporation totals at soil depths of 0, 3, 9, 15, and 21 mm were 32, 25, 16, 10, and 5 mm, respectively. Cumulative evaporation results from the Bowen ratio and heat pulse methods indicated a consistent dynamic pattern for surface and subsurface water evaporation with both time and depth. These findings suggest that heat pulse sensors can accurately measure subsurface soil water evaporation during several wetting–drying cycles.}, number={3}, journal={VADOSE ZONE JOURNAL}, author={Xiao, X. and Horton, R. and Sauer, T. J. and Heitman, J. L. and Ren, T.}, year={2011}, month={Aug}, pages={1016–1022} }
 @book{heitman_white_boyles_austin_2011, place={Raleigh, NC}, title={Improved Statewide Soil Moisture Estimation for Hydrologic Assessment and Forecasting}, number={70251}, institution={NC Water Resources Research Institute}, author={Heitman, J.L. and White, J.G. and Boyles, R. and Austin, R.}, year={2011} }
 @book{meijer_heitman_white_2011, place={Raleigh, NC}, title={Soil Management Can Maximize Water Availability}, number={AG 439 77}, journal={SoilFacts}, institution={North Carolina Cooperative Extension}, author={Meijer, A. and Heitman, J.L. and White, J.G.}, year={2011} }
 @article{taggart_heitman_vepraskas_burchell_2011, title={Surface shading effects on soil C loss in a temperate muck soil}, volume={163}, ISSN={0016-7061}, url={http://dx.doi.org/10.1016/j.geoderma.2011.04.020}, DOI={10.1016/j.geoderma.2011.04.020}, abstractNote={Histosols are a huge reservoir for C, covering < 1% of the world's land surface but storing up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from Histosols is critical for proper management of these C sinks. Two experiments evaluated how formerly cultivated, warm-climate Histosols undergoing wetland restoration respond to decreases in soil temperatures via vegetative shading, under different water table conditions. We compared temperature and soil CO2 efflux differences from intact soil cores under three levels of light reduction in a greenhouse: 0%, 70%, and 90%. Soil in full sun was consistently warmer and showed higher efflux rates than 70% and 90% shade treatments: 4.132, 3.438, and 2.054 μmol CO2 m−2 s−1, respectively. Shade treatments reached peak efflux rates at similar water potential, −2 to − 4 kPa. A field experiment subjected in-situ soil to full sun, 70% light reduction, and light reduction from naturally occurring herbaceous vegetation. Shade treatment effects on soil temperature and C mineralization were evident throughout the growing season. Vegetative shade effects on soil temperature were greatest in August and September when soil under vegetation was 5–11 °C cooler than unshaded soil. Soil CO2 efflux was correlated strongly with soil temperature; daily efflux rates were consistently highest from unshaded soil. Efflux across treatments showed a strong seasonal correlation to soil moisture, increasing as soil dried in response to water table decline. Soil water potential was unaffected by shade treatment, suggesting temperature effects were solely responsible for efflux differences between treatments. All results confirm that surface shading has a strong influence on soil temperatures and C mineralization rates. Management to enhance vegetative shading in wetland restoration projects may be an effective strategy for slowing soil C losses and promoting soil C sequestration when O2 is not limiting.}, number={3-4}, journal={Geoderma}, publisher={Elsevier BV}, author={Taggart, Matthew J. and Heitman, Joshua L. and Vepraskas, Michael J. and Burchell, Michael R.}, year={2011}, month={Jul}, pages={238–246} }
 @article{howard_heitman_bowman_2010, title={A Simple Approach for Demonstrating Soil Water Retention and Field Capacity}, volume={39}, ISSN={1539-1582}, url={http://dx.doi.org/10.4195/jnrlse.2009.0036n}, DOI={10.4195/jnrlse.2009.0036n}, abstractNote={It is difficult to demonstrate the soil water retention relationship and related concepts because the specialized equipment required for performing these measurements is unavailable in most classrooms. This article outlines a low‐cost, easily visualized method by which these concepts can be demonstrated in most any classroom. Columns (62.5 cm tall) were constructed using 25, 2.5 cm tall sections of 7.62‐cm (3‐inch) i.d. polyvinyl chloride pipe, which were connected using transparent tape. Three different soil materials were packed to specified bulk densities in the columns, and saturated with water. These vertical columns were then allowed to drain into a simulated water table 2.5 cm above the bottom of the soil volume until drainage ceased. After drainage, columns were sectioned to determine water content distribution with depth along the column. It was assumed that matric potential was inversely related to height above the water table. Therefore, water content measurements and assumed potentials for each section provided data for a water retention curve with minimum potential of approximately –60 cm. During drainage, measurements of soil matric potential were taken at regular intervals using tensiometers installed within the column, validating assumptions about matric potential. Among soil materials tested, those with narrow particle‐size distributions, ∼100% sand, gave the widest distribution of water contents in the observed matric potential ranges. This method, with proper explanation and execution, may be a valuable learning tool by which visual, auditory, and kinesthetic learners may be better able to understand the concepts pertaining to soil–water retention relationships.}, number={1}, journal={Journal of Natural Resources and Life Sciences Education}, publisher={Wiley}, author={Howard, A. and Heitman, J. L. and Bowman, D.}, year={2010}, pages={120} }
 @article{singer_heitman_hernandez-ramirez_sauer_prueger_hatfield_2010, title={Contrasting methods for estimating evapotranspiration in soybean}, volume={98}, ISSN={["0378-3774"]}, DOI={10.1016/j.agwat.2010.08.014}, abstractNote={Crop scientists are often interested in canopy rather than leaf water estimates. Comparing canopy fluxes for multiple treatments using micrometeorological approaches presents limitations because of the large fetch required. The goal of this study was to compare leaf-scale to field-scale data by summing soil water evaporation (E) and leaf transpiration (T) versus ET using tower eddy covariance (EC) and scaling leaf transpiration to the canopy level using a two-step scaling approach in soybean [Glycine max (L.) Merr.]. Soybean transpiration represented 89–96% of E + T when combining the soil water evaporation with leaf transpiration on the five measurement days during reproductive growth. Comparing E + T versus ET from the EC system, the E + T method overestimated ET from 0.68 to 1.58 mm. In terms of percent difference, the best agreement between the two methods was 15% on DOY 235 and the worst agreement occurred on DOY 234 (41%). A two-step scaling method predicted average ET within 0.01 mm of the EC ET between 10:00 and 14:15 on an hourly time-step on DOY 227 under uniform sky conditions and average ET within 0.03 mm of the EC ET on DOY 235 under intermittent sky conditions between 10:00 and 15:15. Pooling the scaled-leaf data and comparing them with the measured EC ET data exhibited a strong linear relationship (r = 0.835) after accounting for bias (6%). Findings from this study indicate satisfactory results comparing absolute differences are likely not obtainable by summing leaf transpiration with soil water evaporation to calculate canopy water fluxes. However, scaling leaf transpiration provided a robust measure of canopy transpiration during reproductive growth in soybean under these conditions and merits additional study under different climatic and crop conditions.}, number={1}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Singer, Jeremy W. and Heitman, Joshua L. and Hernandez-Ramirez, Guillermo and Sauer, Thomas J. and Prueger, John H. and Hatfield, Jerry L.}, year={2010}, month={Dec}, pages={157–163} }
 @article{drake_jordan_schroeder-moreno_johnson_heitman_cardoza_brandenburg_shew_corbett_bogle_et al._2010, title={Crop Response following Tall Fescue Sod and Agronomic Crops}, volume={102}, ISSN={0002-1962}, url={http://dx.doi.org/10.2134/agronj2010.0236}, DOI={10.2134/agronj2010.0236}, abstractNote={Sod‐based production systems have been successful in the southeastern and mid‐Atlantic regions of the United States as an alternative to conventional tillage systems. However, research comparing these systems in North Carolina is limited. Therefore, research was conducted at four locations in North Carolina to compare corn ( Zea mays L.), cotton ( Gossypium hirsutum L.), peanut ( Arachis hypogaea L.), and soybean [ Glycine max (L.) Merr.] yield when these crops were strip tilled following 4 yr of continuous tall fescue ( Shedonorus phoenix Scop.) vs. 4 yr of either corn or cotton grown in no tillage or strip tillage. Cotton yield was higher following tall fescue compared with yield following agronomic crops. In contrast, yield of corn was lower following tall fescue compared with agronomic crops while peanut and soybean yields were not affected by previous cropping history. Additional treatments in peanut included conventional tillage following both cropping systems, and pod yield was lower when peanut was strip tilled into either tall fescue or residue from corn or cotton compared with conventional tillage systems. No major differences in soil bulk density at depths of 0 to 8 cm or 8 to 16 cm were noted when comparing tall fescue or agronomic crops either in strip tillage or nontilled zones. Populations of soil parasitic nematodes were often lower in peanut following tall fescue than when following agronomic crops. These experiments indicate that sod‐based systems may be an effective alternative to reduced tillage systems, especially for cotton. However, yield benefits were not observed for peanut or soybean and corn was negatively affected by tall fescue.}, number={6}, journal={Agronomy Journal}, publisher={Wiley}, author={Drake, W. L. and Jordan, D. L. and Schroeder-Moreno, M. and Johnson, P. D. and Heitman, J. L. and Cardoza, Y. J. and Brandenburg, R. L. and Shew, B. B. and Corbett, T. and Bogle, C. R. and et al.}, year={2010}, month={Nov}, pages={1692–1699} }
 @article{arya_heitman_2010, title={Hydraulic Conductivity Function from Water Flow Similarity in Idealized- and Natural-Structure Pores}, volume={74}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2009.0204}, abstractNote={Our objective was to develop and evaluate a simple, primarily physically based hydraulic conductivity model for natural‐structure soils. The proposed model of the hydraulic conductivity function, K (θ), is based on particle‐size distribution (PSD), flow in idealized capillary tubes of uniform diameter, and measured saturated hydraulic conductivity ( K s ). We assume that hydraulic conductivity at a given saturation is actually saturated conductivity of pores that remain filled at that saturation, i.e., insignificant contribution from unfilled pores. The PSD data are used to generate pore‐size distribution using the Arya–Paris model, based on soil water characteristics. Pores are first treated as idealized, and flow for each domain is calculated using the Hagen–Poiseuille flow equation. We further assume that the ratio of flow in any pore domain to total flow at saturation for idealized pores applies equally to natural‐structure pores. Using this equality, the total flow at saturation, obtained from measured K s , is distributed among the natural pore domains. This approach is advantageous in that flow parameters remain constant for all soils. Using the model, we calculated K (θ) for 29 soils with a wide range of physical properties. Agreement between predicted and experimental data was excellent to good for 21 soils ( r 2 > 0.9 for 14 soils, >0.8 for 7 soils). Poorer agreement in the remaining soils was attributed to uncertainty in input and experimental K (θ) data. A 1:1 comparison of log‐transformed predicted and experimental data for the 29 soils (719 data pairs) showed significant scatter( r 2 = 0.735, RMSE = 1.04), which is consistent with similar comparisons in the literature.}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Arya, Lalit M. and Heitman, J. L.}, year={2010}, pages={787–796} }
 @article{herring_koenning_heitman_2010, title={Impact of Rotylenchulus reniformis on Cotton Yield as Affected by Soil Texture and Irrigation}, volume={42}, number={4}, journal={Journal of Nematology}, author={Herring, S.L. and Koenning, S.R. and Heitman, J.L.}, year={2010}, month={Dec}, pages={319–323} }
 @article{heitman_horton_sauer_ren_xiao_2010, title={Latent heat in soil heat flux measurements}, volume={150}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2010.04.017}, abstractNote={The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, there remains uncertainty about what comprises soil heat flux and how surface and subsurface heat fluxes are linked in energy balance closure. The objective of this study is to demonstrate the presence of a subsurface latent heat sink, which must be considered in order to accurately link subsurface heat fluxes between depths near and at the soil surface. Measurements were performed under effectively bare surface conditions in a silty clay loam soil near Ames, IA. Soil heat flux was measured with heat-pulse sensors using the gradient heat flux approach at 1-, 3-, and 6-cm soil depths. Independent estimates of the daily latent heat sink were obtained by measuring the change of mass of microlysimeters. Heat flux measurements at the 1-cm depth deviated from heat flux measurements at other depths, even after calorimetric adjustment was made. This deviation was most pronounced shortly after rainfall, where the 1-cm soil heat flux measurement exceeded 400 W m−2. Cumulative soil heat flux measurements at the 1-cm depth exceeded measurements at the 3-cm depth by >75% over a 7-day rain-free period, whereas calorimetric adjustment allowed 3- and 6-cm depth measurements to converge. Latent heat sink estimates from the microlysimeters accounted for nearly all of the differences between the 1- and 3-cm depth heat flux measurements, indicating that the latent heat sink was distributed between the 1- and 3-cm depths shortly after the rainfall event. Results demonstrate the importance of including latent heat when attempts are made to link or extrapolate subsurface soil heat flux measurements to the surface soil heat flux.}, number={7-8}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Heitman, J. L. and Horton, R. and Sauer, T. J. and Ren, T. S. and Xiao, X.}, year={2010}, month={Jul}, pages={1147–1153} }
 @book{meijer_heitman_2010, place={Raleigh, NC}, title={Managing Equipment Traffic to Limit Soil Compaction}, number={AG 439 72}, journal={SoilFacts}, institution={North Carolina Cooperative Extension}, author={Meijer, A. and Heitman, J.L.}, year={2010} }
 @article{arya_heitman_thapa_bowman_2010, title={Predicting Saturated Hydraulic Conductivity of Golf Course Sands from Particle-Size Distribution}, volume={74}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2009.0022}, abstractNote={This research developed a model of saturated hydraulic conductivity for golf course and athletic field media. The model was developed from saturated flow data in packed sand cores, for which a pore‐size distribution was derived from particle‐size distribution, bulk density, and measured soil water characteristic data. The pores were first assumed to form an idealized structure, consisting of non‐tortuous capillary tubes of uniform shape and size, and the Hagen–Poiseuille flow equation was applied to compute idealized saturated flow. The idealized saturated flows were compared with saturated flows derived from the measured saturated hydraulic conductivity data. Subsequently, an empirical relationship was established between the two in the form: Q t(m) = c + dQ t(h–p) , where Q t(m) is the saturated flow through the natural‐structure sand cores and Q t(–p) is the saturated flow through the idealized pore structure for the same core. In our study, parameters c and d had values of −1.675 and 0.308, respectively, and the r 2 of the regression had a value of 0.871. The model was applied to 14 golf course sands and produced excellent results with minor anomalies.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Arya, Lalit M. and Heitman, J. L. and Thapa, B. B. and Bowman, D. C.}, year={2010}, pages={33–37} }
 @inproceedings{heitmann_2010, title={The path forward - evolving science and engineering education to meet the new challenges}, booktitle={Research Progress in Paper Industry and Biorefinery (4th ISETPP), vols 1-3}, author={Heitmann, J.}, year={2010}, pages={32–36} }
 @article{heitman_vepraskas_2009, title={An Example Emphasizing Mass–Volume Relationships for Problem Solving in Soils}, volume={38}, ISSN={1539-1582}, url={http://dx.doi.org/10.4195/jnrlse.2008.0007n}, DOI={10.4195/jnrlse.2008.0007n}, abstractNote={Mass–volume relationships are a useful tool emphasized for problem solving in many geo‐science and engineering applications. These relationships also have useful applications in soil science. Developing soils students’ ability to utilize mass–volume relationships through schematic diagrams of soil phases (i.e., air, water, and solid) can help to facilitate cross‐discipline problem solving efforts encountered throughout their careers. The objective of this article is to provide an applied example emphasizing mass–volume relationships and schematic diagrams for problem solving in soils. The example is taken from a study in restoration of an organic wetland soil. Drainage of organic soils results in a reduction of horizon thickness, termed subsidence , through shrinkage, loss of buoyancy, and oxidation of organic matter. Knowing the amount of subsidence that has occurred is important in restoration efforts, but is difficult to determine from conditions post‐drainage at a given site. Scientists must make use of mass–volume relationship and inference to assess the amount of subsidence that has occurred. In this example, information about post‐drainage and offsite horizon thickness, bulk density, and sand content are used to develop an estimate of the amount of subsidence. General information about the site is presented followed by assumptions used to develop the solution. The problem, assumptions, and step‐by‐step solution are divided into parts to facilitate use as a homework example, lecture example, or group problem solving activity. Questions and discussion points are presented to encourage student development of their own solution to the problem.}, number={1}, journal={Journal of Natural Resources and Life Sciences Education}, publisher={Wiley}, author={Heitman, J. L. and Vepraskas, M. J.}, year={2009}, pages={140} }
 @article{vepraskas_heitman_austin_2009, title={Future directions for hydropedology: quantifying impacts of global change on land use}, volume={13}, ISSN={["1607-7938"]}, DOI={10.5194/hess-13-1427-2009}, abstractNote={Abstract. Hydropedology is well positioned to address contemporary issues resulting from climate change. We propose a six-step process by which digital, field-scale maps will be produced to show where climate change impacts will be greatest for two land uses: a) home sites using septic systems, and b) wetlands. State and federal laws have defined critical water table levels that can be used to determine where septic systems will function well or fail, and where wetlands are likely to occur. Hydrologic models along with historic rainfall and temperature data can be used to compute long records of water table data. However, it is difficult to extrapolate such data across land regions, because too little work has been done to test different ways for doing this reliably. The modeled water table data can be used to define soil drainage classes for individual mapping units, and the drainage classes used to extrapolate the data regionally using existing digital soil survey maps. Estimates of changes in precipitation and temperature can also be input into the models to compute changes to water table levels and drainage classes. To do this effectively, more work needs to be done on developing daily climate files from the monthly climate change predictions. Technology currently exists to use the NRCS Soil Survey Geographic (SSURGO) Database with hydrologic model predictions to develop maps within a GIS that show climate change impacts on septic system performance and wetland boundaries. By using these maps, planners will have the option to scale back development in sensitive areas, or simply monitor the water quality of these areas for pathogenic organisms. The calibrated models and prediction maps should be useful throughout the Coastal Plain region. Similar work for other climate-change and land-use issues can be a valuable contribution from hydropedologists.}, number={8}, journal={HYDROLOGY AND EARTH SYSTEM SCIENCES}, author={Vepraskas, M. J. and Heitman, J. L. and Austin, R. E.}, year={2009}, pages={1427–1438} }
 @book{hoyt_heitman_osmond_cooke_2009, place={Raleigh, NC}, title={Modifying Soil for Plant Growth around Your Home}, number={AG 439 70}, journal={SoilFacts}, institution={North Carolina Cooperative Extension}, author={Hoyt, G. and Heitman, J.L. and Osmond, D.L. and Cooke, A.}, year={2009} }
 @article{davis_horton_heitman_ren_2009, title={Wettability and Hysteresis Effects on Water Sorption in Relatively Dry Soil}, volume={73}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2009.00028n}, DOI={10.2136/sssaj2009.00028N}, abstractNote={The soil water retention curve (SWRC) is a key tool for understanding the fundamental relationship between soil moisture content and its associated energy. The objective of this study was to measure soil water retention including hysteresis at the dry end of the SWRC and to examine the effect of wettability on the SWRCs of two wettable soils and their hydrophobized counterparts. Two conditions, wettable and hydrophobic, were measured for each soil. The method used to measure the SWRCs was vapor equilibration over salt solutions of known osmotic potentials. Free water in the form of individual droplets was found to be present at the surface of the unwashed hydrophobic soils due to decreases in the osmotic potential during the hydrophobizing process. Water droplets did not form on the hydrophilic and washed hydrophobic soils. Soil wettability was found to affect soil water retention in relatively dry soil. The hydrophilic soils used in this study exhibited significant hysteresis in the water potential range of −2.3 to −19.2 MPa. Soil wettability and hysteresis should be considered when studying water sorption and desorption in relatively dry soil.}, number={6}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={Davis, Dedrick D. and Horton, Robert and Heitman, Joshua L. and Ren, Tusheng}, year={2009}, month={Nov}, pages={1947–1951} }
 @article{desutter_sauer_parkin_heitman_2008, title={A Subsurface, Closed-Loop System for Soil Carbon Dioxide and Its Application to the Gradient Efflux Approach}, volume={72}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2006.0101}, DOI={10.2136/sssaj2006.0101}, abstractNote={Carbon dioxide concentrations in the soil can vary both temporally and spatially. Methodology was developed to semicontinuously measure subsurface concentrations of CO 2 using expanded, porous Teflon (ePTFE) tubing. Lengths of ePTFE tubing (7.6 m) were buried at 0.02, 0.1, and 0.18 m below the soil surface in a Harps loam soil (fine‐loamy, mixed, superactive, mesic Typic Calciaquoll) in central Iowa, and also positioned directly on the soil surface (0 m). Soil atmospheric gases that diffused through the walls of the tubing were circulated in a closed‐loop design through solid‐state CO 2 sensors to determine the concentration of CO 2 at each depth. Independent measures of CO 2 concentrations were also determined by sampling the in‐line gas stream of the ePTFE system and from samples extracted from gas wells positioned near the buried tubing. Good agreement ( r 2 > 0.95) was observed between the ePTFE system and the independent measures, with the ePTFE having biases of 1.2 and 1.37 times greater than the in‐line and gas well samples, respectively. The soil‐gas diffusion coefficient of CO 2 ( D s ) was determined using intact soil cores and values were about 2.5 times less than two popular models used to predict D s in soil. Estimates of CO 2 flux using Fick's Law, six approaches to determine the vertical CO 2 concentration gradient, and three methods to determine D s ranged from >800 to <1 μmol m −2 s −1 on Day of the Year 239.5. Although Fick's Law is commonly used to estimate CO 2 flux from soil, the approach used to determine the vertical CO 2 concentration gradient and method used to determine D s can both include sources of uncertainty.}, number={1}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={DeSutter, T. M. and Sauer, T. J. and Parkin, T. B. and Heitman, J. L.}, year={2008}, month={Jan}, pages={126–134} }
 @article{heitman_horton_ren_nassar_davis_2008, title={A test of coupled soil heat and water transfer prediction under transient boundary temperatures}, volume={72}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2007.0234}, abstractNote={Diffusion‐based coupled soil heat and water transfer theory includes capability to describe transient behavior. Unfortunately, laboratory tests of theory typically include a single initial water content distribution with a single set of boundary conditions, rather than providing a set of experimental conditions with a range of measurements for comparison with predictions. Agreement between theory and measurements can result from calibration, but this provides an incomplete test of theory. The objective of this work was to test diffusion‐based coupled heat and water transfer theory by comparing theory‐based predictions with measured transient temperature and water content distributions. Data from a single boundary condition were used for calibration of each of two soils, silt loam and sand. Subsequent testing was performed at additional boundary and initial conditions using measurements from the same soil. Results indicate that the theory can be calibrated for a single boundary condition with adjustment of soil saturated hydraulic conductivity and/or the vapor enhancement factor, which adjust the liquid and vapor fluxes, respectively. For silt loam, calibration reduced Root Mean Square Error (RMSE) by 67 and 18% for water content and temperature distributions, respectively. For sand, RMSE was reduced by 14 and 46% for water content and temperature, respectively. Using this calibration, there was agreement between calculated and measured distributions for additional boundary and initial conditions with RMSE ≤ 0.03 m 3 m −3 and 1.28°C for water content and temperature distributions, respectively. However, when the boundary temperature gradient was instantly reversed, noticeable differences occurred between measured and calculated patterns of heat and moisture redistribution. The theory described observations well when boundary temperature conditions were changed gradually, but results suggested a need for further development of coupled heat and water transfer theory combined with testing under transient conditions to make improvements in the description of transfer mechanisms.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Heitman, J. L. and Horton, R. and Ren, T. and Nassar, I. N. and Davis, D. D.}, year={2008}, pages={1197–1207} }
 @inproceedings{sauer_ochsner_heitman_horton_tanner_akinyemi_hernandez-ramirez_moorman_2008, title={Careful measurements and energy balance closure—The case of soil heat flux}, url={http://ams.confex.com/ams/pdfpapers/138960.pdf}, booktitle={Proceedings of the 28th Conference on Agricultural and Forest Meteorolog}, author={Sauer, Thomas J. and Ochsner, Tyson E. and Heitman, Joshua L. and Horton, Robert and Tanner, Bert D. and Akinyemi, Olukayode D. and Hernandez-Ramirez, Guillermo and Moorman, Thomas B.}, year={2008}, month={Jan} }
 @article{gieselman_heitman_horton_2008, title={Effect of a hydrophobic layer on the upward movement of water under surface-freezing conditions}, volume={173}, ISSN={["1538-9243"]}, DOI={10.1097/SS.0b013e31816d1e75}, abstractNote={A water table can increase the severity of frost heave in soil by providing water for accumulation at the freezing front. Limiting flow from the water table can reduce frost heave. We hypothesized that a hydrophobic soil layer positioned between the freezing front and the water table would restrict water flow and ice accumulation at the freezing front. This hypothesis was tested in laboratory experiments using 20-cm-long soil cells designed to achieve one-dimensional flow conditions between an imposed −5 °C upper boundary and a water table at the lower cell boundary. Experiments were performed with 24 and 10 °C lower boundary temperatures. Dichlorodimethylsilane-treated soil was used to provide a 2-cm thick hydrophobic soil layer above the water table; cells with and without hydrophobic layers were used for comparison. For both lower boundary temperatures, the freezing front advanced more rapidly in the soil cells with hydrophobic layers. Final water uptake volumes corresponded to only 5% of the initial cell pore volume for cells with hydrophobic layers, but more than 20% for cells without hydrophobic layers. Although only slightly larger amounts of frost heave were observed in cells without hydrophobic layers, water contents at the freezing front indicated much greater expansion and deformation within the cells when the hydrophobic layer was absent. Overall, the hydrophobic layer reduced water uptake and ice accumulation at the freezing front.}, number={5}, journal={SOIL SCIENCE}, author={Gieselman, Heath and Heitman, Joshua L. and Horton, Roert}, year={2008}, month={May}, pages={297–305} }
 @article{sauer_akinyemi_thery_heitman_desutter_horton_2008, title={Evaluation of a new, perforated heat flux plate design}, volume={35}, ISSN={["0735-1933"]}, DOI={10.1016/j.icheatmasstransfer.2008.03.012}, abstractNote={Accurate measurement of heat flux is essential to optimize structural and process design and to improve understanding of energy transfer in natural systems. Laboratory and field experiments evaluated the performance of a new, perforated heat flux plate designed to reduce flow distortion for environmental applications. Laboratory tests involving dry and saturated sand showed that performance of the new CAPTEC plate is comparable to a solid, standard REBS plate. Very low thermal gradients may have however led to poor performance of the CAPTEC plate in saturated sand. Water infiltration and redistribution experiments using clayey and sandy soils showed an apparent reduced disruption of liquid water and vapour in the soil surrounding the CAPTEC plate as compared to solid Hukseflux and standard REBS plates. Surface area of REBS plate, though smaller than that of CAPTEC, did not lead to any significantly improved evaporation, due to perforations on CAPTEC plate. Field tests in a loam soil indicated that the CAPTEC plates were durable and produced daily total flux values within ~ 0.15 MJ m− 2 of independent estimates.}, number={7}, journal={INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER}, author={Sauer, T. J. and Akinyemi, O. D. and Thery, P. and Heitman, J. L. and DeSutter, T. M. and Horton, R.}, year={2008}, month={Aug}, pages={800–804} }
 @article{heitman_xiao_horton_sauer_2008, title={Sensible heat measurements indicating depth and magnitude of subsurface soil water evaporation}, volume={44}, ISSN={["0043-1397"]}, DOI={10.1029/2008wr006961}, abstractNote={Most measurement approaches for determining evaporation assume that the latent heat flux originates from the soil surface. Here, a new method is described for determining in situ soil water evaporation dynamics from fine‐scale measurements of soil temperature and thermal properties with heat pulse sensors. A sensible heat balance is computed using soil heat flux density at two depths and change in sensible heat storage in between; the sensible heat balance residual is attributed to latent heat from evaporation of soil water. Comparisons between near‐surface soil heat flux density and Bowen ratio energy balance measurements suggest that evaporation originates below the soil surface several days after rainfall. The sensible heat balance accounts for this evaporation dynamic in millimeter‐scale depth increments within the soil. Comparisons of sensible heat balance daily evaporation estimates to Bowen ratio and mass balance estimates indicate strong agreement ( r 2 = 0.96, root‐mean‐square error = 0.20 mm). Potential applications of this technique include location of the depth and magnitude of subsurface evaporation fluxes and estimation of stage 2–3 daily evaporation without requirements for large fetch. These applications represent new contributions to vadose zone hydrology.}, journal={WATER RESOURCES RESEARCH}, author={Heitman, J. L. and Xiao, X. and Horton, R. and Sauer, T. J.}, year={2008}, month={Oct} }
 @article{heitman_horton_sauer_desutter_2008, title={Sensible heat observations reveal soil-water evaporation dynamics}, volume={9}, ISSN={["1525-755X"]}, DOI={10.1175/2007JHM963.1}, abstractNote={Abstract Soil-water evaporation is important at scales ranging from microbial ecology to large-scale climate. Yet routine measurements are unable to capture rapidly shifting near-surface soil heat and water processes involved in soil-water evaporation. The objective of this study was to determine the depth and location of the evaporation zone within soil. Three-needle heat-pulse sensors were used to monitor soil heat capacity, thermal conductivity, and temperature below a bare soil surface in central Iowa during natural wetting/drying cycles. Soil heat flux and changes in heat storage were calculated from these data to obtain a balance of sensible heat components. The residual from this balance, attributed to latent heat from water vaporization, provides an estimate of in situ soil-water evaporation. As the soil dried following rainfall, results show divergence in the soil sensible heat flux with depth. Divergence in the heat flux indicates the location of a heat sink associated with soil-water evaporation. Evaporation estimates from the sensible heat balance provide depth and time patterns consistent with observed soil-water depletion patterns. Immediately after rainfall, evaporation occurred near the soil surface. Within 6 days after rainfall, the evaporation zone proceeded > 13 mm into the soil profile. Evaporation rates at the 3-mm depth reached peak values > 0.25 mm h−1. Evaporation occurred simultaneously at multiple measured depth increments, but with time lag between peak evaporation rates for depths deeper below the soil surface. Implementation of finescale measurement techniques for the soil sensible heat balance provides a new opportunity to improve understanding of soil-water evaporation.}, number={1}, journal={JOURNAL OF HYDROMETEOROLOGY}, author={Heitman, J. L. and Horton, R. and Sauer, T. J. and Desutter, T. M.}, year={2008}, month={Feb}, pages={165–171} }
 @article{heitman_horton_ren_ochsner_2007, title={An Improved Approach for Measurement of Coupled Heat and Water Transfer in Soil Cells}, volume={71}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2006.0327}, DOI={10.2136/sssaj2006.0327}, abstractNote={Laboratory experiments on coupled heat and water transfer in soil have been limited in their measurement approaches. Inadequate temperature control creates undesired two-dimensional distributions of both temperature and moisture. Destructive sampling to determine soil volumetric water content (θ) prevents measurement of transient θ distributions and provides no direct information on soil thermal properties. The objectives of this work were to: (i) develop an instrumented closed soil cell that provides one-dimensional conditions and permits in situ measurement of temperature, θ, and thermal conductivity (X) under transient boundary conditions, and (ii) test this cell in a series of experiments using four soil type-initial θ combinations and 10 transient boundary conditions. Experiments were conducted using soil-insulated cells instrumented with thermo-time domain reflectometry (T-TDR) sensors. Temperature distributions measured in the experiments show nonlinearity, which is consistent with nonuniform thermal properties provided by thermal moisture distribution but differs from previous studies lacking one-dimensional temperature control. The T-TDR measurements of θ based on dielectric permittivity, volumetric heat capacity, and change in volumetric heat capacity agreed well with post-experiment sampling, providing r 2 values of 0.87, 0.93, and 0.95, respectively. Measurements of θ and λ were also consistent with the shapes of the observed temperature distributions. Techniques implemented in these experiments allowed observation of transient temperature, θ, and λ distributions on the same soil sample for 10 sequentially imposed boundary conditions, including periods of rapid redistribution. This work demonstrates that, through improved measurement techniques, the study of heat and water transfer processes can be expanded in ways previously unavailable.}, number={3}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={Heitman, J. L. and Horton, R. and Ren, T. and Ochsner, T. E.}, year={2007}, month={May}, pages={872–880} }
 @article{heitman_gaur_horton_jaynes_kaspar_2007, title={Field Measurement of Soil Surface Chemical Transport Properties for Comparison of Management Zones}, volume={71}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2006.0254}, DOI={10.2136/sssaj2006.0254}, abstractNote={Management of chemicals in soil is important, yet the complexity of field soils limits prediction of management effects on transport. To date, few methods have been available for field measurement of chemical transport properties, but a recently developed dripper–time domain reflectometry technique allows rapid collection of data for determining these properties. The objective of this work was to apply this technique for comparison of chemical transport properties for different soil management zones. Experiments were conducted comparing four interrow management zones: no‐till nontrafficked, no‐till trafficked, chisel plow nontrafficked, and chisel plow trafficked. Drip emitters were positioned at 12 locations in each zone and used to apply water followed by a step input of CaCl 2 tracer solution. Breakthrough curves were measured via electrical conductivity with time domain reflectometry probes. The mobile–immobile model was fit to the breakthrough curves to determine chemical transport properties. Mean chemical transport properties were 0.34, 0.11 h −1 , 10 cm h −1 , 164 cm 2 h −1 , and 5 cm, for the immobile water fraction, mass exchange coefficient, average pore‐water velocity, mobile dispersion coefficient, and dispersivity, respectively. All five properties showed significant differences between management zones. Differences in mass exchange and mobile dispersion coefficients coincided with differences in tillage, while differences in mean pore water velocities coincided with differences in traffic. The immobile water fraction was largest for the no‐till nontrafficked zone. These results represent one of very few reports for field measurement of chemical transport properties and the first application of this approach for comparison of chemical transport properties across management zones.}, number={2}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={Heitman, J.L. and Gaur, A. and Horton, R. and Jaynes, D. B. and Kaspar, T. C.}, year={2007}, month={Mar}, pages={529–536} }
 @article{zhou_heitman_horton_ren_ochsner_prunty_ewing_sauer_2006, title={Method for Maintaining One-Dimensional Temperature Gradients in Unsaturated, Closed Soil Cells}, volume={70}, ISSN={0361-5995}, url={http://dx.doi.org/10.2136/sssaj2005.0336n}, DOI={10.2136/sssaj2005.0336n}, abstractNote={One‐dimensional temperature gradients are difficult to achieve in nonisothermal laboratory studies because, in addition to desired axial temperature gradients, ambient temperature interference (ATI) creates a radial temperature distribution. Our objective was to develop a closed soil cell with limited ATI. The cell consists of a smaller soil column, the control volume, surrounded by a larger soil column, which provides radial insulation. End boundary temperatures are controlled by a new spiral‐circulation heat exchanger. Four cell size configurations were tested for ATI under varying ambient temperatures. Results indicate that cells with a 9‐cm inner column diameter, 5‐cm concentric soil buffer, and either 10‐ or 20‐cm length effectively achieved one‐dimensional temperature conditions. At 30°C ambient temperature, and with axial temperature gradients as large as 1°C cm −1 , average steady‐state radial temperature gradients in the inner soil columns were <0.02°C cm −1 Thus, these cell configurations meet the goal of maintaining a one‐dimensional temperature distribution. These cells provide new opportunities for improving the study of coupled heat and water movement in soil.}, number={4}, journal={Soil Science Society of America Journal}, publisher={Wiley}, author={Zhou, J. and Heitman, J. L. and Horton, R. and Ren, T. and Ochsner, T. E. and Prunty, L. and Ewing, R. P. and Sauer, T. J.}, year={2006}, month={Jul}, pages={1303–1309} }
 @article{kaleita_heitman_logsdon_2005, title={FIELD CALIBRATION OF THE THETA PROBE FOR DES MOINES LOBE SOILS}, volume={21}, ISSN={1943-7838}, url={http://dx.doi.org/10.13031/2013.19714}, DOI={10.13031/2013.19714}, abstractNote={Knowledge of soil moisture is needed to understand crop water use, hydrology, and microclimate. A reliable, rapidtechnique is needed, and recently an impedance soil moisture probe (Theta Probe) has been accepted by the scientificcommunity. The purposes of this study were to calibrate the probe for soils of Central Iowa through field sampling, todetermine the number of samples needed for calibration, and to determine the effect of temperature on calibration. Laboratorycalibration was conducted on Des Moines lobe soils across a range of water contents and temperatures. Including atemperature term increased the R2 from 0.85 to 0.87. Field calibration was based on Theta Probe measurements on similarsoils combined with gravimetric sampling and soil temperature determination. Although some scatter existed, the fieldcalibration was adequate for Iowa soils (R2 = 0.77). Inclusion of temperature did not significantly improve the calibrationfor the field data. To determine the appropriate number of samples needed for the field calibration, regression equations weredetermined from sample numbers ranging from 2 to 89, and the standard error was determined for each. Based on the standarderror analysis, 20 samples was an adequate number, with no further improvement for additional data points.}, number={5}, journal={Applied Engineering in Agriculture}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Kaleita, A. L. and Heitman, J. L. and Logsdon, S. D.}, year={2005}, pages={865–870} }
 @article{pierzynski_heitman_kulakow_kluitenberg_carlson_2004, title={Revegetation of Waste Fly Ash Landfills in a Semiarid Environment}, volume={57}, ISSN={0022-409X}, url={http://dx.doi.org/10.2307/4003801}, DOI={10.2307/4003801}, number={3}, journal={Journal of Range Management}, publisher={JSTOR}, author={Pierzynski, Gary M. and Heitman, Joshua L. and Kulakow, Peter A. and Kluitenberg, Gerard J. and Carlson, James}, year={2004}, month={May}, pages={312} }
 @article{heitman_basinger_kluitenberg_ham_frank_barnes_2003, title={Field Evaluation of the Dual-Probe Heat-Pulse Method for Measuring Soil Water Content}, volume={2}, ISSN={1539-1663}, url={http://dx.doi.org/10.2113/2.4.552}, DOI={10.2113/2.4.552}, abstractNote={The dual-probe heat-pulse (DPHP) method is useful for measuring water content (θ) and change in water content (Δθ) near the soil surface. The method has been evaluated in laboratory and greenhouse experiments, but not in a field setting. Our objective was to test the DPHP method under field conditions and for a range of soil properties. Twenty-five DPHP sensors and five monitoring stations were constructed and installed at five locations in northeastern Kansas to measure θ and Δθ at 3-h intervals for 3 mo. In addition, θ was estimated by coupling Δθ measurements with independent measurements of θ obtained by soil sampling at sensor installation. Additional soil samples were collected from each location during the monitoring period to provide independent measurements of θ. Regression of DPHP and independent θ measurements revealed slight bias but substantial offset error (about 0.1 m3 m−3) in the DPHP method. The offset error could not be fully attributed to bias in any single input parameter, but could have been caused by a combination of biased parameters. Estimates of θ from Δθ measurements also revealed slight bias, but offset error was considerably smaller. Use of a published empirical calibration for DPHP sensors almost completely eliminated this bias and further reduced the offset error to approximately 0.01 m3 m−3 Thus, the Δθ approach combined with use of the empirical calibration appears to have practical utility.}, number={4}, journal={Vadose Zone Journal}, publisher={Wiley}, author={Heitman, J. L. and Basinger, J. M. and Kluitenberg, G. J. and Ham, J. M. and Frank, J. M. and Barnes, P. L.}, year={2003}, month={Nov}, pages={552–560} }
 @inbook{kluitenberg_heitman_2002, title={Effect of forced convection on soil water content measurement with the dual-probe heat-pulse method}, ISBN={0875909884}, ISSN={0065-8448}, url={http://dx.doi.org/10.1029/129gm23}, DOI={10.1029/129gm23}, abstractNote={This chapter contains sections titled: Introduction Dual-Probe Heat-Pulse Method Heat Transfer Models Error Analysis Methodology Error Analysis Results Summary and Conclusions}, booktitle={Environmental Mechanics: Water, Mass and Energy Transfer in the Biosphere}, publisher={American Geophysical Union}, author={Kluitenberg, Gerard J. and Heitman, Joshua L.}, year={2002}, pages={275–283} }