@article{mathers_robarge_walker_sayde_heitman_2024, title={Laboratory observations for examining estimates of soil dry surface layer thickness with parsimonious models}, volume={7}, ISSN={["2150-3435"]}, DOI={10.1080/02626667.2024.2373249}, journal={HYDROLOGICAL SCIENCES JOURNAL}, author={Mathers, Cara and Robarge, Wayne and Walker, John and Sayde, Chadi and Heitman, Joshua}, year={2024}, month={Jul} }
 @article{baker_battye_robarge_arya_aneja_2020, title={Modeling and measurements of ammonia from poultry operations: Their emissions, transport, and deposition in the Chesapeake Bay}, volume={706}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2019.1115290}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Baker, Jordan and Battye, William H. and Robarge, Wayne and Arya, S. Pal and Aneja, Viney P.}, year={2020}, month={Mar} }
 @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{robarge_duckworth_osmond_smyth_river_2017, title={Commentary on "A possible trade-off between clean air and clean water" by Smith et al. (2017)}, volume={72}, ISSN={["1941-3300"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85033378332&partnerID=MN8TOARS}, DOI={10.2489/jswc.72.6.121a}, abstractNote={Authors of the recent feature article by Smith et al., which was published in the A Section of the July/August 2017 issue of the Journal of Soil and Water Conservation (A Section articles are not peer-reviewed while articles in the Research Section of the journal are peer-reviewed), have conducted water quality research in the Western Lake Erie Basin (WLEB) and demonstrated multiple potential causes of increased soluble phosphorous (SP) loading, including agricultural practice changes such as increased no-till, tile drainage, surface application of fall fertilizer, and weather. In their article, “A possible trade-off between clean air and clean water,” these authors propose an additional cause: the connection between the success of the Clean Air Act in improving air quality in the United States and increases in SP loading that have contributed to harmful algal blooms in the WLEB. Although we agree that scientists must always be vigilant for pernicious consequences of well-meaning actions, we believe that there are flaws in the study design and data interpretation that undermine the conclusion of article. Specifically, what we see as flaws in the interpretation of the data presented in table 1 and figures 2 and 3 are described below. Furthermore, the authors do…}, number={6}, journal={JOURNAL OF SOIL AND WATER CONSERVATION}, author={Robarge, Wayne and Duckworth, Owen and Osmond, Deanna and Smyth, Jot and River, Mark}, year={2017}, pages={121A–122A} }
 @article{kim_lee_kumar_shin_robarge_kim_lee_2016, title={Effects of HCl pretreatment, drying, and storage on the stable isotope ratios of soil and sediment samples}, volume={30}, ISSN={["1097-0231"]}, DOI={10.1002/rcm.7600}, abstractNote={RationaleStable isotope (δ13C, δ15N, δ34S values) analysis has become increasingly important for tracing contaminant sources in environments. Pretreatment of environmental samples allows accurate analysis of stable isotope ratios. The pretreatment of a sample and its subsequent preservation could either contaminate or create experimental artifacts affecting the validity of the resulting C/N ratios and the elemental isotopic contents of a sample.MethodsThe effects of acid pretreatment (0.1, 0.5, 1, 2, 5, 13 M HCl) and exposure period (2, 6, 12, 24, and 48 h) on the stable isotopic ratios of marine sediment (MS), river sediment (RS) and terrestrial soil (TS) samples were evaluated. The effects of storage temperatures (–80, –20 and 2°C), storage duration (1 week, 1 to 12 months) and washing steps (1, 2, 3, 5, 7 or 12 times) on the stable isotopic ratios were also considered. The %C, %N and %S, as well as the δ13C, δ15N, and δ34S values, of each sample were measured using continuous flow Elemental Analyzer/Isotope Ratio Mass Spectrometry (EA/IRMS).ResultsThe HCl treatment was applicable for δ13C analysis. However, the acid concentration and duration of exposure that brought about total removal of carbonate for the three sample types varied; e.g. the TS sample required stronger acid and a shorter exposure time. Storage time also had an effect: the δ13C values were lower and the δ15N and δ34S values higher after storage for 300 days.ConclusionsHCl pretreatment effectively eliminates carbonates and thereby helps δ13C analysis of the organic fraction. HCl pretreatment is not recommended for δ15N and δ34S analysis. Freeze‐drying of samples is recommended rather than oven drying. A temperature‐dependent change in the isotopic ratios of long‐term stored samples was observed during this study; therefore, relatively short‐term storage (–80°C) of freeze‐dried samples is preferable. Copyright © 2016 John Wiley & Sons, Ltd.}, number={13}, journal={RAPID COMMUNICATIONS IN MASS SPECTROMETRY}, author={Kim, Min-Seob and Lee, Won-Seok and Kumar, K. Suresh and Shin, Kyung-Hoon and Robarge, Wayne and Kim, Minseok and Lee, Sang Ryong}, year={2016}, month={Jul}, pages={1567–1575} }
 @article{spence_walker_robarge_preston_osmond_2015, title={Comparing nitrous oxide losses from three residential landscapes under different management schemes following natural rainfall events}, volume={18}, ISSN={["1573-1642"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84949200350&partnerID=MN8TOARS}, DOI={10.1007/s11252-015-0453-9}, number={4}, journal={URBAN ECOSYSTEMS}, author={Spence, Porche L. and Walker, John T. and Robarge, Wayne P. and Preston, Bill and Osmond, Deanna L.}, year={2015}, month={Dec}, pages={1227–1243} }
 @article{king_darrah_money_meentemeyer_maguire_nye_michener_murtha_jirtle_murphy_et al._2015, title={Geographic clustering of elevated blood heavy metal levels in pregnant women}, volume={15}, ISSN={["1471-2458"]}, DOI={10.1186/s12889-015-2379-9}, abstractNote={Cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As) exposure is ubiquitous and has been associated with higher risk of growth restriction and cardiometabolic and neurodevelopmental disorders. However, cost-efficient strategies to identify at-risk populations and potential sources of exposure to inform mitigation efforts are limited. The objective of this study was to describe the spatial distribution and identify factors associated with Cd, Pb, Hg, and As concentrations in peripheral blood of pregnant women. Heavy metals were measured in whole peripheral blood of 310 pregnant women obtained at gestational age ~12 weeks. Prenatal residential addresses were geocoded and geospatial analysis (Getis-Ord Gi* statistics) was used to determine if elevated blood concentrations were geographically clustered. Logistic regression models were used to identify factors associated with elevated blood metal levels and cluster membership. Geospatial clusters for Cd and Pb were identified with high confidence (p-value for Gi* statistic <0.01). The Cd and Pb clusters comprised 10.5 and 9.2 % of Durham County residents, respectively. Medians and interquartile ranges of blood concentrations (μg/dL) for all participants were Cd 0.02 (0.01–0.04), Hg 0.03 (0.01–0.07), Pb 0.34 (0.16–0.83), and As 0.04 (0.04–0.05). In the Cd cluster, medians and interquartile ranges of blood concentrations (μg/dL) were Cd 0.06 (0.02–0.16), Hg 0.02 (0.00–0.05), Pb 0.54 (0.23–1.23), and As 0.05 (0.04–0.05). In the Pb cluster, medians and interquartile ranges of blood concentrations (μg/dL) were Cd 0.03 (0.02–0.15), Hg 0.01 (0.01–0.05), Pb 0.39 (0.24–0.74), and As 0.04 (0.04–0.05). Co-exposure with Pb and Cd was also clustered, the p-values for the Gi* statistic for Pb and Cd was <0.01. Cluster membership was associated with lower education levels and higher pre-pregnancy BMI. Our data support that elevated blood concentrations of Cd and Pb are spatially clustered in this urban environment compared to the surrounding areas. Spatial analysis of metals concentrations in peripheral blood or urine obtained routinely during prenatal care can be useful in surveillance of heavy metal exposure.}, number={1}, journal={BMC PUBLIC HEALTH}, publisher={Springer Science and Business Media LLC}, author={King, Katherine E. and Darrah, Thomas H. and Money, Eric and Meentemeyer, Ross and Maguire, Rachel L. and Nye, Monica D. and Michener, Lloyd and Murtha, Amy P. and Jirtle, Randy and Murphy, Susan K. and et al.}, year={2015}, month={Oct} }
 @article{walker_robarge_austin_2014, title={Modeling of ammonia dry deposition to a pocosin landscape downwind of a large poultry facility}, volume={185}, ISSN={["1873-2305"]}, DOI={10.1016/j.agee.2013.10.029}, abstractNote={A semi-empirical bi-directional flux modeling approach is used to estimate NH3 air concentrations and dry deposition fluxes to a portion of the Pocosin Lakes National Wildlife Refuge (PLNWR) downwind of a large poultry facility. Meteorological patterns at PLNWR are such that some portion of the refuge is downwind of the poultry facility 52%, 66%, 57%, and 50% of time during winter, spring, summer, and fall, respectively. Air concentrations and dry deposition rates are highest in the northeasterly direction from the facility, consistent with prevailing wind patterns. Dry deposition rates along the axis of highest concentrations are 10.1 kg N ha−1 yr−1 at the refuge boundary closest to the facility, decreasing to 5.4 kg N ha−1 yr−1 1.5 km further downwind and continuing to decrease non-linearly to a deposition rate of 1.4 kg N ha−1 yr−1 8–10 km downwind. Approximately 10% of the refuge model domain receives ≥3.0 kg N ha−1 yr−1 as dry NH3 deposition. Depending on the definition of the background air concentration, annual nitrogen loading to the refuge from background NH3 dry deposition and NH3 dry deposition associated with elevated concentrations downwind of the facility is between 41% and 79% higher than background dry NH3 deposition alone. Relative to the total N deposition budget for the refuge, which includes all nitrogen compounds, total background N deposition plus NH3 dry deposition associated with elevated concentrations downwind of the facility is, correspondingly, 6–10% greater than background total N deposition alone. From a process standpoint, predicted fluxes are most sensitive to uncertainty in the parameterization of the cuticular resistance.}, journal={AGRICULTURE ECOSYSTEMS & ENVIRONMENT}, author={Walker, John T. and Robarge, Wayne P. and Austin, Robert}, year={2014}, month={Mar}, pages={161–175} }
 @article{walker_jones_bash_myles_meyers_schwede_herrick_nemitz_robarge_2013, title={Processes of ammonia air-surface exchange in a fertilized Zea mays canopy}, volume={10}, ISSN={["1726-4189"]}, DOI={10.5194/bg-10-981-2013}, abstractNote={Abstract. Recent incorporation of coupled soil biogeochemical and bi-directional NH3 air–surface exchange algorithms into regional air quality models holds promise for further reducing uncertainty in estimates of NH3 emissions from fertilized soils. While this represents a significant advancement over previous approaches, the evaluation and improvement of such modeling systems for fertilized crops requires process-level field measurements over extended periods of time that capture the range of soil, vegetation, and atmospheric conditions that drive short-term (i.e., post-fertilization) and total growing season NH3 fluxes. This study examines the processes of NH3 air–surface exchange in a fertilized corn (Zea mays) canopy over the majority of a growing season to characterize soil emissions after fertilization and investigate soil–canopy interactions. Micrometeorological flux measurements above the canopy, measurements of soil, leaf apoplast and dew/guttation chemistry, and a combination of in-canopy measurements, inverse source/sink, and resistance modeling were employed. Over a period of approximately 10 weeks following fertilization, daily mean and median net canopy-scale fluxes yielded cumulative total N losses of 8.4% and 6.1%, respectively, of the 134 kg N ha−1 surface applied to the soil as urea ammonium nitrate (UAN). During the first month after fertilization, daily mean emission fluxes were positively correlated with soil temperature and soil volumetric water. Diurnally, maximum hourly average fluxes of ≈ 700 ng N m−2 s−1 occurred near mid-day, coincident with the daily maximum in friction velocity. Net emission was still observed 5 to 10 weeks after fertilization, although mid-day peak fluxes had declined to ≈ 125 ng N m−2 s−1. A key finding of the surface chemistry measurements was the observation of high pH (7.0–8.5) in leaf dew/guttation, which reduced the ability of the canopy to recapture soil emissions during wet periods. In-canopy measurements near peak leaf area index (LAI) indicated that the concentration of NH3 just above the soil surface was highly positively correlated with soil volumetric water, which likely reflects the influence of soil moisture on resistance to gaseous diffusion through the soil profile and hydrolysis of remaining urea. Inverse source/sink and resistance modeling indicated that the canopy recaptured ≈ 76% of soil emissions near peak LAI. Stomatal uptake may account for 12–34% of total uptake by foliage during the day compared to 66–88% deposited to the cuticle. Future process-level NH3 studies in fertilized cropping systems should focus on the temporal dynamics of net emission to the atmosphere from fertilization to peak LAI and improvement of soil and cuticular resistance parameterizations.
                    }, number={2}, journal={BIOGEOSCIENCES}, author={Walker, J. T. and Jones, M. R. and Bash, J. O. and Myles, L. and Meyers, T. and Schwede, D. and Herrick, J. and Nemitz, E. and Robarge, W.}, year={2013}, pages={981–998} }
 @article{lee_yates_robarge_bradford_2013, title={Synergistic ammonia losses from animal wastewater}, volume={71}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2013.01.046}, abstractNote={Thin-layer models are commonly used to estimate NH3 emissions from liquid waste. However, such models differ in their ability to accurately reproduce observed emissions, which may be partly due to an incomplete mechanistic understanding of NH3 volatilization. In this study, NH3 release from pure solutions of (NH4)2SO4 (AS), swine pit liquid (PL), swine lagoon liquid (LL), dairy lagoon liquid (DLL), and dairy manure liquid (DML) were evaluated under controlled conditions (pH 7.6 and temperature 20 °C). Relationships between the NH3 release and pH, temperature, and total ammoniacal nitrogen (TAN) were established. Under similar TAN conditions, the NH3 release was higher for PL, LL, DLL, and DML than for AS. Pure solutions of AS that were spiked with NaHCO3 showed NH3 emissions rates that were comparable to DML, DLL, LL and PL. The enhanced NH3 emissions of PL, LL, DLL and DML were therefore explained by linkages between TAN and HCO3−.}, journal={ATMOSPHERIC ENVIRONMENT}, author={Lee, Sang R. and Yates, Scott R. and Robarge, Wayne P. and Bradford, Scott A.}, year={2013}, month={Jun}, pages={245–250} }
 @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.xAbstract:  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® B3 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} }
 @misc{ni_robarge_xiao_heber_2012, title={Volatile organic compounds at swine facilities: A critical review}, volume={89}, ISSN={["0045-6535"]}, DOI={10.1016/j.chemosphere.2012.04.061}, abstractNote={Volatile organic compounds (VOCs) are regulated aerial pollutants that have environmental and health concerns. Swine operations produce and emit a complex mixture of VOCs with a wide range of molecular weights and a variety of physicochemical properties. Significant progress has been made in this area since the first experiment on VOCs at a swine facility in the early 1960s. A total of 47 research institutions in 15 North American, European, and Asian countries contributed to an increasing number of scientific publications. Nearly half of the research papers were published by U.S. institutions. Investigated major VOC sources included air inside swine barns, in headspaces of manure storages and composts, in open atmosphere above swine wastewater, and surrounding swine farms. They also included liquid swine manure and wastewater, and dusts inside and outside swine barns. Most of the sample analyses have been focusing on identification of VOC compounds and their relationship with odors. More than 500 VOCs have been identified. About 60% and 10% of the studies contributed to the quantification of VOC concentrations and emissions, respectively. The largest numbers of VOC compounds with reported concentrations in a single experimental study were 82 in air, 36 in manure, and 34 in dust samples. The relatively abundant VOC compounds that were quantified in at least two independent studies included acetic acid, butanoic acid (butyric acid), dimethyl disulfide, dimethyl sulfide, iso-valeric, p-cresol, propionic acid, skatole, trimethyl amine, and valeric acid in air. They included acetic acid, p-cresol, iso-butyric acid, butyric acid, indole, phenol, propionic acid, iso-valeric acid, and skatole in manure. In dust samples, they were acetic acid, propionic acid, butyric acid, valeric acid, p-cresol, hexanal, and decanal. Swine facility VOCs were preferentially bound to smaller-size dusts. Identification and quantification of VOCs were restricted by using instruments based on gas Chromatography (GC) and liquid chromatography (LC) with different detectors most of which require time-consuming procedures to obtain results. Various methodologies and technologies in sampling, sample preparation, and sample analysis have been used. Only four publications reported using GC based analyzers and PTR-MS (proton-transfer-reaction mass spectrometry) that allowed continuous VOC measurement. Because of this, the majority of experimental studies were only performed on limited numbers of air, manure, or dust samples. Many aerial VOCs had concentrations that were too low to be identified by the GC peaks. Although VOCs emitted from swine facilities have environmental concerns, only a few studies investigated VOC emission rates, which ranged from 3.0 to 176.5 mg d−1 kg−1 pig at swine finishing barns and from 2.3 to 45.2 g d−1 m−2 at manure storages. Similar to the other pollutants, spatial and temporal variations of aerial VOC concentrations and emissions existed and were significantly affected by manure management systems, barn structural designs, and ventilation rates. Scientific research in this area has been mainly driven by odor nuisance, instead of environment or health concerns. Compared with other aerial pollutants in animal agriculture, the current scientific knowledge about VOCs at swine facilities is still very limited and far from sufficient to develop reliable emission factors.}, number={7}, journal={CHEMOSPHERE}, author={Ni, Ji-Qin and Robarge, Wayne P. and Xiao, Changhe and Heber, Albert J.}, year={2012}, month={Oct}, pages={769–788} }
 @article{fry_brown_lloyd_hansen_legleiter_robarge_spears_2011, title={Effect of dietary boron on physiological responses in growing steers inoculated with bovine herpesvirus type-1}, volume={90}, ISSN={["1532-2661"]}, DOI={10.1016/j.rvsc.2010.04.016}, abstractNote={Thirty-six Angus and Angus×Simmental steers were fed one of three dietary treatments; (1) control (no supplemental B), (2) 5 mg supplemental B/kg, and (3) 15 mg supplemental B/kg for 47 days to determine the effects of dietary boron (B) on disease resistance following an inoculation with bovine herpesvirus type-1 (BHV-1). On day 34 of the study steers were inoculated intranasally with BHV-1. Rectal temperatures began to elevate at day 2, and plasma tumor necrosis factor-α concentrations increased (P<0.05) by day 2 following BHV-1 inoculation. Plasma acute phase proteins were increased (P<0.01) while plasma interferon-γ was decreased (P<0.05) by day 4 post-inoculation. Supplementation of B increased (P<0.001) plasma B concentrations in a dose-responsive manner. However, dietary B did not affect the duration and severity of clinical signs of BHV-1 and had minimal effects on plasma acute phase proteins and cytokines.}, number={1}, journal={RESEARCH IN VETERINARY SCIENCE}, author={Fry, R. S. and Brown, T. T., Jr. and Lloyd, K. E. and Hansen, S. L. and Legleiter, L. R. and Robarge, W. P. and Spears, J. W.}, year={2011}, month={Feb}, pages={78–83} }
 @article{bash_walker_katul_jones_nemitz_robarg_2010, title={Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field}, volume={44}, ISSN={["0013-936X"]}, DOI={10.1021/es9037269}, abstractNote={An analytical model was developed to describe in-canopy vertical distribution of ammonia (NH(3)) sources and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy mean NH(3) concentration and wind speed profiles. This model was applied to quantify in-canopy air-surface exchange rates and above-canopy NH(3) fluxes in a fertilized corn (Zea mays) field. Modeled air-canopy NH(3) fluxes agreed well with independent above-canopy flux estimates. Based on the model results, the urea fertilized soil surface was a consistent source of NH(3) one month following the fertilizer application, whereas the vegetation canopy was typically a net NH(3) sink with the lower portion of the canopy being a constant sink. The model results suggested that the canopy was a sink for some 70% of the estimated soil NH(3) emissions. A logical conclusion is that parametrization of within-canopy processes in air quality models are necessary to explore the impact of agricultural field level management practices on regional air quality. Moreover, there are agronomic and environmental benefits to timing liquid fertilizer applications as close to canopy closure as possible. Finally, given the large within-canopy mean NH(3) concentration gradients in such agricultural settings, a discussion about the suitability of the proposed model is also presented.}, number={5}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Bash, Jesse O. and Walker, John T. and Katul, Gabriel G. and Jones, Matthew R. and Nemitz, Eiko and Robarg, Wayne P.}, year={2010}, month={Mar}, pages={1683–1689} }
 @article{cooter_bash_walker_jones_robarge_2010, title={Estimation of NH3 bi-directional flux from managed agricultural soils}, volume={44}, ISSN={["1352-2310"]}, DOI={10.1016/j.atmosenv.2010.02.044}, abstractNote={The Community Multi-Scale Air Quality model (CMAQ) is used to assess regional air quality conditions for a wide range of chemical species throughout the United States (U.S.). CMAQ representation of the regional nitrogen budget is limited by its treatment of ammonia (NH3) soil emission from, and deposition to underlying surfaces as independent rather than tightly coupled processes, and by its reliance on soil emission estimates that do not respond to variable meteorology and ambient chemical conditions. The present study identifies an approach that addresses these limitations, lends itself to regional application, and will better position CMAQ to meet future assessment challenges. These goals were met through the integration of the resistance-based flux model of Nemitz et al. (2001) with elements of the United States Department of Agriculture EPIC (Environmental Policy Integrated Climate) model. Model integration centers on the estimation of ammonium and hydrogen ion concentrations in the soil required to estimate soil NH3 flux. The EPIC model was calibrated using data collected during an intensive 2007 field study in Lillington, North Carolina. A simplified process model based on the nitrification portion of EPIC was developed and evaluated. It was then combined with the Nemitz et al. (2001) model and measurements of near-surface NH3 concentrations to simulate soil NH3 flux at the field site. Finally, the integrated flux (emission) results were scaled upward and compared to recent national ammonia emission inventory estimates. The integrated model results are shown to be more temporally resolved (daily), while maintaining good agreement with established soil emission estimates at longer time-scales (monthly). Although results are presented for a single field study, the process-based nature of this approach and NEI comparison suggest that inclusion of this flux model in a regional application should produce useful assessment results if nationally consistent sources of driving soil and agricultural management information are identified.}, number={17}, journal={ATMOSPHERIC ENVIRONMENT}, author={Cooter, Ellen J. and Bash, Jesse O. and Walker, John T. and Jones, M. R. and Robarge, Wayne}, year={2010}, month={Jun}, pages={2107–2115} }
 @article{muruganandam_israel_robarge_2010, title={Nitrogen Transformations and Microbial Communities in Soil Aggregates from Three Tillage Systems}, volume={74}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2009.0006}, abstractNote={Quantifying N transformation processes in soil aggregates is relevant since microbial communities central to the N cycle may differ among aggregate size fractions. Our objective was to test the hypothesis that variations in microbial community composition of aggregate size fractions influence N transformation rates of soil from three long‐term (22‐yr) tillage systems (no‐till, chisel plow, and moldboard plow). Aggregate size fractions (2–4, 0.5–1, and <0.25 mm) were obtained by dry sieving. Nitrogen transformation rates were estimated by analysis of 15N pool dilution data with the FLUAZ model, and microbial community composition by phospholipid fatty acid (PLFA) profiles. Aggregate size fraction and tillage system had significant (P < 0.01) effects on total and microbial biomass C and N, gross N mineralization rate (GNMR), gross nitrification rate (GNR), and gross N immobilization rate (GIR). No‐till soils and the 0.5‐ to 1.0‐mm aggregate size fraction had the highest N transformation rates. Net N mineralization rates were greater for no‐till than for tilled soils. Multiple response permutation analysis of PLFA data revealed that microbial community composition did not differ with aggregate size fraction. Stepwise regression analysis indicated that microbial community composition (nonmetric multidimensional scaling Axis 1) accounted for 89% of the variation in GIR, soil C and N concentrations accounted for 88% of the variation in GNMR, and microbial biomass C concentration accounted for 81% of the variation in GNR. These results indicate that greater N transformation rates in no‐till than tilled soil were due primarily to increased microbial biomass (i.e., microbial population size) rather than altered microbial community composition.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Muruganandam, Subathra and Israel, Daniel W. and Robarge, Wayne P.}, year={2010}, pages={120–129} }
 @article{muruganandam_israel_robarge_2009, title={Activities of Nitrogen-Mineralization Enzymes Associated with Soil Aggregate Size Fractions of Three Tillage Systems}, volume={73}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2008.0231}, abstractNote={Nitrogen mineralization occurring near the soil surface of agroecosystems determines the quantity of plant‐available N, and soil enzymes produced by microorganisms play significant roles in the N mineralization process. Tillage systems may influence soil microbial communities and N mineralization enzymes through alterations in total soil C and N. Soil aggregates of different sizes provide diverse microhabitats for microorganisms and therefore influence soil enzyme activities. Our objective was to test the hypothesis that activities of N mineralization enzymes increase with aggregate size and in no‐till compared with tilled systems. Potential activities of N‐acetyl glucosaminidase (NAG), arylamidase, l‐glutaminase, and l‐asparaginase were measured in five aggregate size fractions (<0.25, 0.25–0.5, 0.5–1, 1–2, and 2–4 mm) obtained from soils of three long‐term (22‐yr) tillage systems (no‐till, chisel plow, and moldboard plow). All enzyme activities were significantly (P < 0.05) greater in no‐till than in tilled systems and positively correlated (P < 0.005) with potential N mineralization. Potential activities of NAG, l‐glutaminase, and arylamidase were significantly greater (P < 0.05) in the intermediate (0.5–1‐mm) aggregate size than in other size fractions. All enzyme activities were positively correlated with total soil C (P < 0.0001), N (P < 0.05), and microbial biomass C (P < 0.05). Aggregate size had significant effects on NAG, arylamidase, and l‐glutaminase activities but the magnitudes were small. Fungal biomarkers (18:2ω6c and 16:1ω5c) determined by the phospholipid fatty acid (PLFA) method were significantly greater in the no‐till than in tilled systems and positively correlated with all enzyme activities. This suggests that no‐till management enhances activities of N mineralization enzymes by enhancing the proportion of fungal organisms in the soil microbial community.}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Muruganandam, Subathra and Israel, Daniel W. and Robarge, Wayne P.}, year={2009}, pages={751–759} }
 @article{freeman_lewbart_robarge_harms_law_stoskopf_2009, title={Characterizing eversion syndrome in captive scyphomedusa jellyfish}, volume={70}, ISSN={["0002-9645"]}, DOI={10.2460/ajvr.70.9.1087}, abstractNote={Abstract
Objective—To determine whether Scyphomedusa jellyfish with eversion syndrome had alterations in husbandry conditions, elemental content, or histologic appearance, compared with unaffected jellyfish.
Animals—123 jellyfish (44 with eversion syndrome and 79 without) at 6 institutions.
Procedures—Elemental analyses were performed on 24 jellyfish with eversion syndrome and 49 without, and histologic examinations were performed on 20 jellyfish with eversion syndrome and 30 without. A questionnaire distributed to 39 institutions with Scyphomedusa jellyfish was used to gather information about husbandry, environmental conditions, and prevalence of eversion syndrome.
Results—For the 39 institutions that responded to the questionnaire, prevalence of eversion syndrome ranged from 0% to 30%. For Aurelia aurita, eversion was more common at institutions with only captive-raised and no wild-caught jellyfish. Eversion was most common among young (approx 1- to 2-month-old) growing jellyfish and older (> 6-month-old) jellyfish. Elemental analysis revealed only minor differences between affected and unaffected jellyfish, with great variation among jellyfish from the same institution and among jellyfish from different institutions. Striated muscle degeneration and necrosis and extracellular matrix (mesoglea) degeneration were evident on histologic examination of affected jellyfish.
Conclusions and Clinical Relevance—Results suggested that eversion syndrome is a complex phenomenon associated with degenerative changes of the bell matrix.}, number={9}, journal={American Journal of Veterinary Research}, author={Freeman, K.S. and Lewbart, G.A. and Robarge, W.P. and Harms, C.A. and Law, J.M. and Stoskopf, M.K.}, year={2009}, month={Sep}, pages={1087–1093} }
 @article{fry_lloyd_jacobi_siciliano_robarge_spears_2010, title={Effect of dietary boron on immune function in growing beef steers*}, volume={94}, ISSN={["0931-2439"]}, DOI={10.1111/j.1439-0396.2008.00906.x}, abstractNote={SummaryThirty‐six Angus and Angus × Simmental cross steers (initial BW 269.5 ± 22.3 kg) were used to determine the effects of dietary boron (B) on performance and immune function. Steers were fed on one of the three dietary treatments: (i) control (no supplemental B; 7.2 mg B/kg DM), (ii) 5 mg supplemental B/kg DM and (iii) 50 mg supplemental B/kg DM, from sodium borate for 78 days. Supplementation of dietary B had no effect on body weight (BW) gain, feed intake or gain:feed during the study. Jugular blood samples were collected prior to feeding on days 28, 63 and 77 for plasma‐B analysis. Supplementation of dietary B increased (p < 0.001) plasma B‐concentration in a dose‐responsive manner. Furthermore, plasma B‐concentration was correlated (p < 0.001; R2 = 0. 95) to daily B‐intake (mg B/day). Jugular blood was also collected, from an equal number of steers from each treatment, on day 42 or 44 for determination of in vitro production of interferon‐γ and tumour necrosis factor‐α from isolated monocytes and assessment of lymphocyte proliferation. Dietary B did not affect T‐ or B‐lymphocyte proliferation or in vitro cytokine production from monocytes. On day 49 of the study, the humoral immune response was assessed by i.m. injection of a 25% pig red blood cell (PRBC) solution for determination of anti‐PRBC IgG and IgM titre responses. Boron‐supplemented steers had greater (p = 0.035) anti‐PRBC IgG titres than controls on day 7 but not on day 14 or 21 post‐injection. Anti‐PRBC IgM titres did not differ throughout the sampling period. Results from this study indicate that supplemental B had minimal effects on immune function and did not affect performance of growing steers.}, number={3}, journal={JOURNAL OF ANIMAL PHYSIOLOGY AND ANIMAL NUTRITION}, author={Fry, R. S. and Lloyd, K. E. and Jacobi, S. K. and Siciliano, P. D. and Robarge, W. P. and Spears, J. W.}, year={2010}, month={Jun}, pages={273–279} }
 @article{wu_walker_schwede_peters-lidard_dennis_robarge_2009, title={A new model of bi-directional ammonia exchange between the atmosphere and biosphere: Ammonia stomatal compensation point}, volume={149}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2008.08.012}, abstractNote={A new multi-layer canopy resistance model of bi-directional NH3 exchange is presented. This new model, which is based on the Multi-Layer BioChemical deposition (MLBC) model [Wu, Y., Brashers, B., Finkelstein, P.L., Pleim, J.E., 2003a. A multiplayer biochemical dry deposition model. I. Model formulation. J. Geophys. Res. 108, D1; Wu, Y., Brashers, B., Finkelstein, P.L., Pleim, J.E., 2003b. A multiplayer biochemical dry deposition model. II. Model evaluation. J. Geophys. Res. 108, D1], incorporates a parameterization for the ammonia stomatal compensation point that is theoretically derived to consider the effects of leaf temperature and apoplastic concentrations of NH4+ and H+. The new ammonia stomatal compensation point scheme accounts for the effects of deposition, emission and leaf temperature on the dynamics of apoplast [NH4+] and [H+]. The new model is evaluated against bidirectional NH3 fluxes measured over fertilized soybean. The general patterns of observed deposition and emission are successfully reproduced when the ammonia stomatal compensation point is included. Driven by the effects of deposition, emission and leaf temperature, modeled apoplastic [NH4+] and [H+] display significant diurnal variation when the buffer effect of the underlying metabolic processes generating or consuming NH4+ were ignored. Model predictive capability is improved slightly by incorporating the feedback into a dynamic stomatal compensation point. A simple implementation of the feedback mechanism in the current model provides opportunities for improvement. While the stomatal flux is shown to be an important process in the regulation of canopy-scale fluxes, it appears that exchange with leaf surface water and soil may also be important.}, number={2}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Wu, Yihua and Walker, John and Schwede, Donna and Peters-Lidard, Christa and Dennis, Robin and Robarge, Wayne}, year={2009}, month={Feb}, pages={263–280} }
 @article{aneja_arya_rumsey_kim_bajwa_arkinson_semunegus_dickey_stefanski_todd_et al._2008, title={Characterizing ammonia emissions from swine farms in eastern North Carolina: Part 2 - Potential environmentally superior technologies for waste treatment}, volume={58}, ISSN={["2162-2906"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-53849100726&partnerID=MN8TOARS}, DOI={10.3155/1047-3289.58.9.1145}, abstractNote={Abstract The need for developing environmentally superior and sustainable solutions for managing the animal waste at commercial swine farms in eastern North Carolina has been recognized in recent years. Program OPEN (Odor, Pathogens, and Emissions of Nitrogen), funded by the North Carolina State University Animal and Poultry Waste Management Center (APWMC), was initiated and charged with the evaluation of potential environmentally superior technologies (ESTs) that have been developed and implemented at selected swine farms or facilities. The OPEN program has demonstrated the effectiveness of a new paradigm for policy-relevant environmental research related to North Carolina’s animal waste management programs. This new paradigm is based on a commitment to improve scientific understanding associated with a wide array of environmental issues (i.e., issues related to the movement of N from animal waste into air, water, and soil media; the transmission of odor and odorants; disease-transmitting vectors; and airborne pathogens). The primary focus of this paper is on emissions of ammonia (NH3) from some potential ESTs that were being evaluated at full-scale swine facilities. During 2-week-long periods in two different seasons (warm and cold), NH3 fluxes from water-holding structures and NH3 emissions from animal houses or barns were measured at six potential EST sites: (1) Barham farm—in-ground ambient temperature anaerobic digester/energy recovery/greenhouse vegetable production system; (2) BOC #93 farm—upflow biofiltration system—EKOKAN ; (3) Carrolls farm—aerobic blanket system—ISSUES-ABS; (4) Corbett #1 farm—solids separation/gasification for energy and ash recovery centralized system—BEST; (5) Corbett #2 farm—solid separation/reciprocating water technology—ReCip; and (6) Vestal farm—Recycling of Nutrient, Energy and Water System—ISSUES—RENEW. The ESTs were compared with similar measurements made at two conventional lagoon and spray technology (LST) farms (Moore farm and Stokes farm). A flow-through dynamic chamber system and two sets of open-path Fourier transform infrared (OP-FTIR) spectrometers measured NH3 fluxes continuously from water-holding structures and emissions from housing units at the EST and conventional LST sites. A statisticalobservational model for lagoon NH3 flux was developed using a multiple linear regression analysis of 15-min averaged NH3 flux data against the relevant environmental parameters measured at the two conventional farms during two different seasons of the year. This was used to compare the water-holding structures at ESTs with those from lagoons at conventional sites under similar environmental conditions. Percentage reductions in NH3 emissions from different components of each potential EST, as well as the whole farm on which the EST was located were evaluated from the estimated emissions from water-holding structures, barns, etc., all normalized by the appropriate nitrogen excretion rate at the potential EST farm, as well as from the appropriate conventional farm. This study showed that ammonia emissions were reduced by all but one potential EST for both experimental periods. However, on the basis of our evaluation results and analysis and available information in the scientific literature, the evaluated alternative technologies may require additional technical modifications to be qualified as unconditional ESTs relative to NH3 emissions reductions.}, number={9}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Aneja, Viney P. and Arya, S. Pal and Rumsey, Ian C. and Kim, D. -S. and Bajwa, K. and Arkinson, H. L. and Semunegus, H. and Dickey, D. A. and Stefanski, L. A. and Todd, L. and et al.}, year={2008}, month={Sep}, pages={1145–1157} }
 @article{aneja_arya_kim_rumsey_arkinson_semunegus_bajwa_dickey_stefanski_todd_et al._2008, title={Characterizing ammonia emissions from swine farms in eastern north carolina: Part 1-conventional lagoon and spray technology for waste treatment}, volume={58}, ISSN={["1047-3289"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-53849107841&partnerID=MN8TOARS}, DOI={10.3155/1047-3289.58.9.1130}, abstractNote={Abstract Ammonia (NH3) fluxes from waste treatment lagoons and barns at two conventional swine farms in eastern North Carolina were measured. The waste treatment lagoon data were analyzed to elucidate the temporal (seasonal and diurnal) variability and to derive regression relationships between NH3 flux and lagoon temperature, pH and ammonium content of the lagoon, and the most relevant meteorological parameters. NH3 fluxes were measured at various sampling locations on the lagoons by a flow-through dynamic chamber system interfaced to an environmentally controlled mobile laboratory. Two sets of open-path Fourier transform infrared (FTIR) spectrometers were also used to measure NH3 concentrations for estimating NH3 emissions from the animal housing units (barns) at the lagoon and spray technology (LST) sites.Two different types of ventilation systems were used at the two farms. Moore farm used fan ventilation, and Stokes farm used natural ventilation. The early fall and winter season intensive measurement campaigns were conducted during September 9 to October 11, 2002 (lagoon temperature ranged from 21.2 to 33.6 °C) and January 6 to February 2, 2003 (lagoon temperature ranged from 1.7 to 12 °C), respectively. Significant differences in seasonal NH3 fluxes from the waste treatment lagoons were found at both farms. Typical diurnal variation of NH3 flux with its maximum value in the afternoon was observed during both experimental periods. Exponentially increasing flux with increasing surface lagoon temperature was observed, and a linear regression relationship between logarithm of NH3 flux and lagoon surface temperature (T l) was obtained. Correlations between lagoon NH3 flux and chemical parameters, such as pH, total Kjeldahl nitrogen (TKN), and total ammoniacal nitrogen (TAN) were found to be statistically insignificant or weak. In addition to lagoon surface temperature, the difference (D) between air temperature and the lagoon surface temperature was also found to influence the NH3 flux, especially when D > 0 (i.e., air hotter than lagoon). This hot-air effect is included in the statistical-observational model obtained in this study, which was used further in the companion study (Part II), to compare the emissions from potential environmental superior technologies to evaluate the effectiveness of each technology.}, number={9}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Aneja, Viney P. and Arya, S. Pal and Kim, D. -S. and Rumsey, Ian C. and Arkinson, H. L. and Semunegus, H. and Bajwa, K. S. and Dickey, D. A. and Stefanski, L. A. and Todd, L. and et al.}, year={2008}, month={Sep}, pages={1130–1144} }
 @article{ryan_overton_speight_oldenburg_loo_robarge_franzen_feldheim_2007, title={Cellular uptake of gold nanoparticles passivated with BSA-SV40 large T antigen conjugates}, volume={79}, ISSN={["1520-6882"]}, DOI={10.1021/ac0715524}, abstractNote={Internalization and subcellular localization in HeLa cells of gold nanoparticles modified with the SV40 large T antigen were quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). Internalization was monitored as a function of incubation time, temperature, nanoparticle diameter, and large T surface coverage. Increasing the amount of large T peptides per gold nanoparticle complex, by either increasing the coverage at constant nanoparticle diameter or by increasing the nanoparticle diameter at constant large T coverage, resulted in more cellular internalization. In addition, nuclear fractionation was performed to quantify nuclear localization of these complexes as a function of large T coverage. In contrast to our prior qualitative investigations of nuclear localization by video-enhanced color differential interference contrast microscopy (VEC-DIC), ICP-OES was able to detect nanoparticles inside fractionated cell nuclei. Although increasing the large T coverage was found to afford higher cell internalization and nuclear targeting, quantitative evaluation of cytotoxicity revealed that higher large T coverages also resulted in greater cytotoxicity. The ICP-OES and nuclear fractionation techniques reported here are valuable tools that can add important quantitative information to optical and electron imaging methods such as VEC-DIC and transmission electron microscopy regarding the fate of nanoparticles in cells.}, number={23}, journal={ANALYTICAL CHEMISTRY}, author={Ryan, Joseph A. and Overton, K. Wesley and Speight, Molly E. and Oldenburg, Christine M. and Loo, Lina and Robarge, Wayne and Franzen, Stefan and Feldheim, Daniel L.}, year={2007}, month={Dec}, pages={9150–9159} }
 @article{walker_spence_kimbrough_robarge_2008, title={Inferential model estimates of ammonia dry deposition in the vicinity of a swine production facility}, volume={42}, ISSN={["1873-2844"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41449099938&partnerID=MN8TOARS}, DOI={10.1016/j.atmosenv.2007.06.004}, abstractNote={This project investigates NH3 dry deposition around a commercial swine production facility in eastern North Carolina. Passive diffusion-tube samplers were used to measure weekly integrated NH3 concentrations at 22 locations along horizontal gradients from the barn/lagoon emissions complex (source) out to a distance of 700 m. A two-layer canopy compensation point model was used to predict bi-directional NH3 exchange within a 500 m circular buffer surrounding the source. The model takes into account differences in soil and vegetation emission potential, as well as canopy physical characteristics, among three primary surfaces surrounding the site: forest, crops spray fertilized with swine waste, and other fertilized crops. Between June 2003 and July 2005, mean observed NH3 concentrations ranged from 169.0 μg NH3 m−3 at a distance of 10 m from the source to 7.1 and 13.0 μg NH3 m−3 at 612 and 698 m in the predominant upwind and downwind directions, respectively. Median predicted dry deposition rates ranged from 145 kg NH3–N ha−1 yr−1 at 10 m from the source to 16 kg NH3–N ha−1 yr−1 at 500 m, which is ≈3.5× wet deposition of NH4+–N. Assuming a steady-state emission factor of 7.0 kg NH3 animal−1 yr−1 and a median population of 4900 animals, NH3 dry deposition over the nearest 500 m from the barn/lagoon complex accounted for 10.4% (3567 kg NH3) of annual emissions (34,300 kg NH3). A model sensitivity analysis shows that predicted deposition rates are more sensitive to assumptions regarding cuticular uptake relative to soil and vegetation emission potentials.}, number={14}, journal={ATMOSPHERIC ENVIRONMENT}, author={Walker, John and Spence, Porche' and Kimbrough, Sue and Robarge, Wayne}, year={2008}, month={Apr}, pages={3407–3418} }
 @article{walker_robarge_wu_meyers_2006, title={Measurement of bi-directional ammonia fluxes over soybean using the modified Bowen-ratio technique}, volume={138}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2006.03.011}, abstractNote={Measurements of bi-directional ammonia (NH3) exchange over a fertilized soybean canopy are presented for an 8-week period during the summer of 2002. The modified Bowen-ratio approach was used to determine fluxes from vertical NH3 and temperature gradients in combination with eddy covariance sensible heat fluxes. The measurement site is located in an area of high NH3 emissions from animal production and fertilizer use. Ambient NH3 concentrations ranged from 0.01 to 43.9 μg m−3 (μ = 9.4 μg m−3) during the experiment. The mean flux was −12.3 ng m−2 s−1, indicating that the canopy was a net sink for NH3; however, emission fluxes were consistently observed during the late morning and early afternoon. Deposition rates were highest when the canopy was wet (μ = −29.9 ng m−2 s−1). Modeling results suggest that uptake via the leaf cuticle was the dominant deposition process and stomatal uptake only occurred during the first few hours after sunrise when the stomatal resistance and compensation point were low. The average stomatal compensation point was high (χs = 11.5 μg NH3 m−3), primarily due to high daytime temperatures (μ = 29 °C). Measured cuticular resistances were large (median Rw = 208 s m−1), most likely due to very dry conditions. The average NH3 flux corresponds to a dry-to-wet deposition ratio of 0.44. Median flux error was 51%, which was dominated by uncertainty in the vertical NH3 gradient due to sequential sampling between measurement heights.}, number={1-4}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Walker, J. T. and Robarge, W. P. and Wu, Y. and Meyers, T. P.}, year={2006}, month={Aug}, pages={54–68} }
 @article{yu_dennis_roselle_nenes_walker_eder_schere_swall_robarge_2005, title={An assessment of the ability of three-dimensional air quality models with current thermodynamic equilibrium models to predict aerosol NO3-}, volume={110}, ISSN={["2169-8996"]}, DOI={10.1029/2004jd004718}, abstractNote={The partitioning of total nitrate (TNO3) and total ammonium (TNH4) between gas and aerosol phases is studied with two thermodynamic equilibrium models, ISORROPIA and the aerosol inorganics model (AIM), and three data sets: high time resolution measurement data from the 1999 Atlanta Supersite Experiment (summer case) and the 2002 Pittsburgh Air Quality Study (PAQS) Supersite Experiment (winter case), and 12‐hour measurement data from the Clinton site, North Carolina, in 1999. At the Atlanta site, both models reproduced a large percentage of the observed aerosol NH4+ and HNO3 (NH4+: >94% and HNO3: >86%) within a factor of 1.5, whereas neither model reproduced a majority of observed aerosol NO3− and NH3 (NO3−: <48% and NH3: <51%) within a factor of 2. At the Pittsburgh site, both models reproduced more than 76% of observed NO3− within a factor of 2. At the Clinton site, both models performed a little better on aerosol NO3− (47–58% within a factor of 1.5) than at the Atlanta site but worse than at the Pittsburgh site. Sensitivity test of thermodynamic models with Gaussian random errors indicates that in many cases, measurement errors in SO42− and TNH4 can explain a major fraction of the discrepancies between the equilibrium model predictions and observations in partitioning of TNO3. Comparison of predictions of the three‐dimensional (3‐D) Community Multiscale Air Quality (CMAQ) model with the observations over the continental United States indicates that the performance of the 3‐D model for NO3−, HNO3, NH4+, and NH3 strongly depends on its performance for TNO3, TNH4, and SO42−. Tests show that errors associated with SO42− and TNH4 predictions of the 3‐D model can result in the thermodynamic model calculation replicating only 47% and 60% of base case NO3− within a factor of 2 for summer and winter cases, respectively. It was found that errors in TNH4 are more critical than errors in SO42− to prediction of NO3−.}, number={D7}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Yu, SC and Dennis, R and Roselle, S and Nenes, A and Walker, J and Eder, B and Schere, K and Swall, J and Robarge, W}, year={2005}, month={Feb} }
 @article{walker_robarge_shendrikar_kimball_2006, title={Inorganic PM2.5 at a US agricultural site}, volume={139}, ISSN={["0269-7491"]}, DOI={10.1016/j.envpol.2005.05.019}, abstractNote={In this study, we present approximately two years (January 1999–December 2000) of atmospheric NH3, NH4+, HCl, Cl−, HNO3, NO3−, SO2, and SO4 concentrations measured by the annular denuder/filter pack method at an agricultural site in eastern North Carolina. This site is influenced by high NH3 emissions from animal production and fertilizer use in the surrounding area and neighboring counties. The two-year mean NH3 concentration is 5.6 (±5.13) μg m−3. The mean concentration of total inorganic PM2.5, which includes SO4, NO3−, NH4+, and Cl−, is 8.0 (±5.84) μg m−3. SO4, NO3−, NH4+, and Cl− represent, respectively, 53, 24, 22, and 1% of measured inorganic PM2.5. NH3 contributes 72% of total NH3 + NH4+, on an average. Equilibrium modeling of the gas + aerosol NH3/H2SO4/HNO3 system shows that inorganic PM2.5 is more sensitive to reductions in gas + aerosol concentrations of sulfate and nitrate relative to NH3.}, number={2}, journal={ENVIRONMENTAL POLLUTION}, author={Walker, JT and Robarge, WP and Shendrikar, A and Kimball, H}, year={2006}, month={Jan}, pages={258–271} }
 @article{walker_whitall_robarge_paerl_2004, title={Ambient ammonia and ammonium aerosol across a region of variable ammonia emission density}, volume={38}, ISSN={["1352-2310"]}, DOI={10.1016/j.atmosenv.2003.11.027}, abstractNote={We present 1 year of ambient ammonia (NH3), ammonium (NH4+), hydrochloric acid (HCl), chloride (Cl−), nitric acid (HNO3), nitrate (NO3−), nitrous acid (HONO), sulfur dioxide (SO2), and sulfate (SO42−) concentrations at three sites in the Coastal Plain region of North Carolina. The three sites, Clinton, Kinston, and Morehead City, are located in counties with total NH3 emission densities of 4800, 2280, and 320 kg NH3-N km−2 yr−1, respectively. Average NH3 concentrations were 5.32, 2.46, and 0.58 μg m−3 at Clinton, Kinston, and Morehead City, respectively. Average NH4+ concentrations were 1.84, 1.25, and 0.91 μg m−3, and total concentrations of inorganic (NH4++NO3−+ SO42−+Cl−) particulate matter with aerosol diameters <2.5 μm (PM2.5) were 8.66, 6.35, and 5.31 μg m−3 at Clinton, Kinston, and Morehead City, respectively. NH3 concentrations were highest during the summer at all sites, with summer-to-winter concentration ratios of 2.40, 5.70, and 1.70 at Clinton, Kinston, and Morehead City, respectively. NH3 concentrations were higher at night at the Clinton site, during the day at the Kinston site, and day vs. night concentrations were similar at the Morehead City site. NH4+ concentrations were highest during the winter at all sites, though this may not be representative of all years. Average daytime concentrations of NH4+ were similar to night values at all sites. NH4+ aerosol was primarily associated with SO42− at all sites, though the degree of SO42− neutralization was highest at Clinton and lowest at Morehead City. NH4+ aerosol formation appeared to be acid-gas-limited at the Clinton site during all seasons and during the spring and summer at the Kinston site. This study shows that agricultural NH3 emissions influence local ambient concentrations of NH3 and PM2.5.}, number={9}, journal={ATMOSPHERIC ENVIRONMENT}, author={Walker, JT and Whitall, DR and Robarge, W and Paerl, HW}, year={2004}, month={Mar}, pages={1235–1246} }
 @inbook{robarge_boos_proctor_2004, title={Determination of trace metal content of fertilizer source materials produced in north America}, volume={872}, DOI={10.1021/bk-2004-0872.ch006}, abstractNote={There is increasing concern over the trace metal content of fertilizers and their subsequent application to agricultural and urban lands. It is feared that continued addition of trace metals to soils via fertilizers poses potential risks to farm families and to consumers of farm products. In order to assess this potential risk, it is necessary to know the trace metal content of fertilizer source materials. This study was undertaken to generate a statistically valid sampling of fertilizer source material produced in North America, and to determine the trace metal content (As, Cd, Cr, Cu, Mo, Ni, Pb, Se, V, U and Zn) of the resulting composite samples generated by the sampling protocol using modern analytical instrumentation and accepted good laboratory practices. The results support the general hypothesis that phosphate bearing source materials do contain varying levels of trace metals. The results also demonstrate that non-phosphate bearing N-P-K source materials do not contain significant amounts of trace metals and should not be considered significant sources of metals when added to agricultural or urban soils. Agreement of analyses from an interlaboratory comparison demonstrate the suitability of the analytical protocols used in this study.}, number={2004}, booktitle={Environmental impact of fertilizer on soil and water}, publisher={Washington, D.C.: Transportation Research Board}, author={Robarge, W. P. and Boos, D. and Proctor, C.}, year={2004}, pages={75–89} }
 @book{william l. hall_wayne p. robarge_2004, title={Environmental impact of fertilizer on soil and water}, DOI={10.1021/bk-2004-0872}, abstractNote={Fertilizers contribute to the variety, abundance, and low cost of food stuffs available to the public. However, fertilizer misuse can lower air, soil, and water quality. Regulators are scrutinizing fertilizers now more than ever because of their impact on the environment. This book provides an analysis of perchlorate in highly dissolved solid matrices and health issues of trace metals in fertilizers. This book focuses on nutrient impacts to water and the environment. Contributors include state and federal regulators, industry professionals, environmental consultants, and those in academia.}, publisher={Washington, DC: American Chemical Society ;|a[New York?]: distributed by Oxford University Press}, author={William L. Hall, editor and Wayne P. Robarge, editor}, year={2004} }
 @article{miner_humenik_rice_rashash_williams_robarge_harris_sheffield_2003, title={Evaluation of a permeable, 5 cm thick, polyethylene foam lagoon cover}, volume={46}, DOI={10.13031/2013.15442}, abstractNote={Anaerobic lagoons and liquid manure storage basins are widely used for the treatment and storage of livestock and poultry manure. Although relatively inexpensive to construct, these devices have been widely criticized based upon their odor and ammonia release. A floating, permeable, composite cover manufactured from recycled polyethylene chips topped with a geotextile layer containing zeolite particles was evaluated under both laboratory and field conditions. Under laboratory conditions, the cover was found essentially to eliminate odor release and to reduce ammonia emissions by approximately 80%. When installed on a 0.4 ha swine manure lagoon in eastern North Carolina, the cover survived severe storms and allowed even intense rainfall to pass through without causing cover inundation. Under these field conditions, the cover was found to reduce ammonia emissions approximately 80%. Odor emissions measured twice during one month of the study were consistently low in concentration and near neutral relative to quality, as determined by an analysis by a trained odor panel. Microbiological examination of the cover after four months of use showed an active population of aerobic bacteria and protozoa; analysis showed that nitrifying, sulfide oxidizing, and methanotrophic bacteria were likely trophic components of the microbial populations observed. The surface of the cover became covered with an algal population within two weeks of installation. This and other vegetative growth had no discernable impact on the performance of the cover.}, number={5}, journal={Transactions of the ASAE}, author={Miner, J. R. and Humenik, F. J. and Rice, J. M. and Rashash, D. M. C. and Williams, C. and Robarge, W. and Harris, D. B. and Sheffield, R.}, year={2003}, pages={1421–1426} }
 @inbook{weber_robarge_hall_averitt_2004, title={Perchlorate in fertilizer? A product defense story}, volume={872}, DOI={10.1021/bk-2004-0872.ch003}, abstractNote={In 1999, a paper entitled Perchlorate Identification In Fertilizers was published which implicated a number of lawn and garden fertilizers and fertilizer source materials as containing perchlorate (1). After re-analyzing these samples using unproved sampling and analytical protocols, most of the fertilizer source materials were found not to contain perchlorate (non-detectable amounts). Perchlorate was still present, to a lesser extent, in several fertilizer source materials and all of the original lawn and garden products. However, no perchlorate has been found in any subsequent analyses of the same products that were later purchased (2). To further investigate this issue, IMC-Global, the world's largest producer and marketer of concentrated phosphate and potash crop nutrients for the agricultural industry, initiated its own analysis program to survey for the possible presence of perchlorate in fertilizer source materials and lawn and garden products, and in samples archived as part of its quality control program. Additional historical samples were recovered from the Magruder check sample program managed through AAPFCO (3). Lastly, IMC Global also participated in several round-robin studies organized by the US Environmental Protection Agency and The Fertilizer Institute (4) to systematically evaluate whether perchlorate does or should be expected to occur in fertilizers.}, number={2004}, booktitle={Environmental impact of fertilizer on soil and water}, publisher={Washington, D.C.: Transportation Research Board}, author={Weber, L. D. and Robarge, W. P. and Hall, W. L. and Averitt, D.}, year={2004}, pages={32–44} }
 @article{robarge_walker_mcculloch_murray_2002, title={Atmospheric concentrations of ammonia and ammonium at an agricultural site in the southeast United States}, volume={36}, ISSN={["1873-2844"]}, DOI={10.1016/S1352-2310(02)00171-1}, abstractNote={In this study, we present ∼1 yr (October 1998–September 1999) of 12-hour mean ammonia (NH3), ammonium (NH4+), hydrochloric acid (HCl), chloride (Cl−), nitrate (NO3−), nitric acid (HNO3), nitrous acid (HONO), sulfate (SO42−), and sulfur dioxide (SO2) concentrations measured at an agricultural site in North Carolina's Coastal Plain region. Mean gas concentrations were 0.46, 1.21, 0.54, 5.55, and 4.15 μg m−3 for HCl, HNO3, HONO, NH3, and SO2, respectively. Mean aerosol concentrations were 1.44, 1.23, 0.08, and 3.37 μg m−3 for NH4+, NO3−, Cl−, and SO42−, respectively. Ammonia, NH4+, HNO3, and SO42− exhibit higher concentrations during the summer, while higher SO2 concentrations occur during winter. A meteorology-based multivariate regression model using temperature, wind speed, and wind direction explains 76% of the variation in 12-hour mean NH3 concentrations (n=601). Ammonia concentration increases exponentially with temperature, which explains the majority of variation (54%) in 12-hour mean NH3 concentrations. Dependence of NH3 concentration on wind direction suggests a local source influence. Ammonia accounts for >70% of NHx (NHx=NH3+NH4+) during all seasons. Ammonium nitrate and sulfate aerosol formation does not appear to be NH3 limited. Sulfate is primarily associated ammonium sulfate, rather than bisulfate, except during the winter when the ratio of NO3−–NH4+ is ∼0.66. The annual average NO3−–NH4+ ratio is ∼0.25.}, number={10}, journal={ATMOSPHERIC ENVIRONMENT}, author={Robarge, WP and Walker, JT and McCulloch, RB and Murray, G}, year={2002}, month={Apr}, pages={1661–1674} }
 @article{cassel_afyuni_robarge_2002, title={Manganese distribution and patterns of soil wetting and depletion in a Piedmont hillslope}, volume={66}, DOI={10.2136/sssaj2002.9390}, abstractNote={The distribution of Mn in soils across the landscape is a function of mineralogy, topography, vegetation, and soil properties that control soil water movement and solute transport. We hypothesized (i) that current landscape properties and processes would explain the observed distribution of acid‐extractable soil Mn in a cropped hillslope in the Carolina Slate Belt of the southern Piedmont, and (ii) that the current spatial patterns of soil water movement would be related to the observed Mn distribution. Soil samples were collected in 10‐cm increments to the 1‐m depth at 5‐m intervals along 110‐m‐long Transect AB and at 10‐m intervals along 80‐m‐long Transect CD. The air‐dried samples were analyzed for acid‐extractable (1 M HCl) Mn. Soil water content (θ) along the transects was periodically monitored by neutron attenuation to the 120‐cm depth. Duplicate banks of tensiometers were installed at depths of 30, 45, and 60 cm at these locations. The concentration of acid‐extractable soil Mn was greatest in the footslope (FS), exceeding values >500 and 600 mg kg−1 soil for Transects AB and CD, respectively. For a wet period in July 1989, θ along Transect AB varied from 0.40 m3 m−3 for the FS to 0.50 m3 m−3 at the summit and was significantly correlated with clay content. Increases in water content of a dry soil after rainfall of 80 mm in July 1989 were similar at all landscape positions, but further increases following additional rainfall were less for the FS, indicating that soil at the FS was already near saturation. The slightly coarser‐textured FS consistently had the lowest water contents. Tensiometric and lateral Br transport data for this site, coupled with the water content measurements, indicate that subsurface flow of water and dissolved Mn from higher to lower elevations on the hillslopes is occurring.}, number={3}, journal={Soil Science Society of America Journal}, author={Cassel, D. K. and Afyuni, M. M. and Robarge, W. P.}, year={2002}, pages={939–947} }
 @article{robarge_mcculloch_cure_2000, title={Atmospheric concentrations of ammonia and ammonium aerosols in eastern north Carolina}, ISBN={1892769123}, journal={Air pollution from agricultural operations : proceedings of the 2nd international conference, October 9-11, 2000, Des Moines, Iowa}, publisher={St. Joseph, Mich. : American Society of Agricultural Engineers}, author={Robarge, W. P. and McCulloch, R. B. and Cure, W.}, year={2000}, pages={10} }
 @article{jones_liehr_classen_robarge_2000, title={Mechanisms of dinitrogen gas formation in anaerobic lagoons}, volume={4}, DOI={10.1016/s1093-0191(00)00016-2}, abstractNote={Anaerobic lagoons have been widely used to treat agricultural waste and waste from small municipalities for many years. Oxidation of ammonia is generally assumed to not occur in such lagoons because of their anaerobic environment. Nitrification, the most likely process that would lead to ammonia oxidation, has not been considered a significant process in anaerobic lagoons because of the negligible concentrations of dissolved oxygen measured in these systems. Therefore observed nitrogen losses are usually assumed to be due to ammonia volatilization. However, in field studies of primary swine waste lagoons in the south-eastern US Coastal Plain, rates of dinitrogen (N2) gas production have been observed to be much greater than rates of NH3 volatilization. This paper discusses possible mechanisms that could explain observations of N2 gas generation in anaerobic waste lagoons. Chemical and microbial reactions have been documented that combine ammonia with nitrite, or nitrous acid, to form N2 under anaerobic conditions. Nitrification and denitrification reactions have also been observed under microaerobic conditions. Each of these reactions requires low levels of oxygen for the initial nitrification of ammonia to nitrite. Diffusion rates of oxygen through the lagoon surface appear to be adequate to allow enough nitrite formation to explain observed N2 fluxes.}, number={2}, journal={Advances in Environmental Research}, author={Jones, M. L. and Liehr, S. K. and Classen, John and Robarge, W.}, year={2000}, pages={133–139} }
 @inproceedings{robert_crouse_mikkelsen_heiniger_robarge_2000, title={Spatial variability of soil pH, phosphorus, copper and zinc in fields receiving long-term applications of animal manure}, number={2000}, booktitle={Animal, agriculture and food processing waste: 8th Symposium: American Society of Agriculture Engineers, 2000}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Robert, B. and Crouse, D.A. and Mikkelsen, R.L. and Heiniger, R. and Robarge, W.}, year={2000}, pages={597–601} }
 @article{duffera_robarge_mikkelsen_1999, title={Estimating the availability of nutrients from processed swine lagoon solids through incubation studies}, volume={70}, ISSN={["0960-8524"]}, DOI={10.1016/S0960-8524(99)00039-5}, abstractNote={Potential environmental hazards from the excess accumulation of swine (Sus scrofa domesticus) manure in eastern North Carolina and new state guidelines on treatment alternatives have necessitated the reevaluation of best management practices for disposal of swine waste (manure and effluent) as a fertilizer source on local crop land. Creation of a value-added product is one viable means of utilizing and economically redistributing the nutrients in swine manure. Incubation studies using four agricultural soils from eastern North Carolina were conducted with pelletized processed swine lagoon solids (PSLS) (1.7% N, 2.5% P, 0.12% Cu and 0.18% Zn) composed of dewatered swine lagoon sludge plus rock flour. The PSLS was added at three application rates (0, 200, 400 mg N kg−1 soil) and incubated for 16 weeks at 25°C. The soil was sampled at 0, 1, 2, 4, 8, 12, and 16 weeks and analyzed for NO3–N, NH4–N and Mehlich III-extractable P, Zn, and Cu. High concentrations of NH4–N and low concentrations of NO3–N were present in the soils shortly after addition of PSLS. After the second week, extractable NH4–N dropped to <4 mg kg−1, while the soil concentration of NO3–N increased rapidly. The amount of NO3–N generated reached 90% of its final value after the fourth week. Across the four soils, 24–35% of the added N, 15–50% of the added P, 20–50% of the added Zn and 15–20% of the added Cu was extractable after 8 weeks. The PSLS is an excellent source of P, but may require additional N if used as a fertilizer source for most row crops.}, number={3}, journal={BIORESOURCE TECHNOLOGY}, author={Duffera, M and Robarge, WP and Mikkelsen, RL}, year={1999}, month={Dec}, pages={261–268} }
 @article{duffera_robarge_mikkelsen_1999, title={Greenhouse evaluation of processed swine lagoon solids as a fertilizer source}, volume={22}, ISSN={["0190-4167"]}, DOI={10.1080/01904169909365748}, abstractNote={Abstract The highly concentrated nature of the swine (Sus scrofa domesticus) production industry in the Coastal Plain region of North Carolina, along with economic constraints that discourage transport of the swine effluent more than a few kilometers from the site of production, result in frequent and repeated application of swine effluent to the same agricultural fields or pastures. Creation of value‐added products and marketing as a fertilizer is an alternative means of redistributing nutrients that are concentrated regionally. Fertilizer equivalency greenhouse studies were conducted to evaluate the potential for processed swine lagoon solids (PSLS) formulated from dewatered swine lagoon solids and rock flour to serve as a fertilizer source for agricultural crops. Sweet corn (Zea mays L.), sorghum (Sorghum bicolor L.), and field bean (Phaseolus vulgaris L.) were grown for six weeks, and common bermudagrass (Cynodon dactylon L. Pers.) was grown for 18 weeks on a Norfolk sandy loam (fine‐loamy, Kaolinitic...}, number={11}, journal={JOURNAL OF PLANT NUTRITION}, author={Duffera, M and Robarge, WP and Mikkelsen, RL}, year={1999}, pages={1701–1715} }
 @article{roelle_aneja_j o'connor_robarge_kim_levine_1999, title={Measurement of nitrogen oxide emissions from an agricultural soil with a dynamic chamber system}, volume={104}, ISSN={["2169-8996"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033585537&partnerID=MN8TOARS}, DOI={10.1029/98JD01202}, abstractNote={Biogenic soil emissions of nitric oxide (NO) were measured from an intensively managed agricultural row crop (corn, Zea mays) during a 4 week period (May 15 through June 9, 1995). The site was located in Washington County, near the town of Plymouth, which is in the Lower Coastal Plain of North Carolina. Soil NO flux was determined using a dynamic flowthrough chamber technique. The measurement period was characterized by two distinguishing features: an application of nitrogen (N) fertilizer at the midpoint of the experiment and a nontypical rainfall pattern. Average NO flux prior to the application of N fertilizer was 31.5 ± 10.1 ng N m−2 s−1, and more than doubled (77.7 ± 63.7 ng N m−2 s−1) after the application of a side‐dressing of N fertilizer. Average soil extractable nitrogen values did not change significantly following application of the side‐dressing of N fertilizer. We attribute this failure to detect a significant difference in soil extractable nitrogen following N fertilization to the method in which the fertilizer was applied, the subsequent rainfall pattern, and the technique of soil sampling. NO flux followed the same diurnal trend as soil temperature, with maximum NO emissions coinciding with maximum soil temperature, and minimum NO emissions coinciding with minimum soil temperature. NO flux was found to increase exponentially with soil temperature, but only after fertilization. Due to subsurface irrigation practices employed by the farmer, changes in soil water content were minimal, and no relation could be drawn between soil water content and NO flux. Simultaneous measurements of NOy, NO2, and NO emissions revealed that NO and NO2 emissions represent 86 and 8.7%, respectively, of NOy emissions leaving the soil. Simultaneous NO flux measurements made by a closed box flux technique, at the same site, revealed no statistically significant differences between the two different methodologies for measuring NO flux.}, number={D1}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Roelle, P and Aneja, VP and J O'Connor and Robarge, W and Kim, DS and Levine, JS}, year={1999}, month={Jan}, pages={1609–1619} }
 @article{beck_robarge_buol_1999, title={Phosphorus retention and release of anions and organic carbon by two Andisols}, volume={50}, ISSN={["1365-2389"]}, DOI={10.1046/j.1365-2389.1999.00213.x}, abstractNote={SummaryAndisols can absorb large amounts of phosphorus rapidly, and then release it slowly, yet the mechanisms by which they retain P and release it for plant growth are poorly understood. Ligand exchange of organic compounds from Al–humic complexes by P and/or Si release – due to breakdown of allophanic microstructure to provide sorption sites – might account for the retention of P, but its extent is not known. We applied a soil column flow‐through technique to quantify the release of anions and organic carbon (C) associated with P sorption by two andic soils, and we related the anion release to possible mechanisms for the retention of P. Phosphate (H2PO4–, HPO42–) sorption and concurrent anion desorption were obtained by passing a 1‐g P 1–1 (32 mmol KH2PO4 in 1 mm CaCl2) solution through the soil columns (25 cm3). Total dissolved P, Fe, Al, S, Ca, Mg, K, Mn, organic C and pH were determined in the eluent. Changes in eluent pH and the patterns of the retention of P and corresponding concentrations of Al, Si and organic C in the eluent were similar for the two Andisols. The general pattern and changes in pH of the eluent coincided with changes in the patterns of release of organic C and Si and the rate of P retention. Release of silica accounted for < 6% of the P sorbed and had only a minor role in P retention in these two Andisols. Release of organic C, however, accounted on a molar basis for 40% and 83%, respectively, of the P sorbed. Direct measurements of the pH of the eluent and release of anions and organic C concurrent to P retention contribute to rapid assessment of the controlling mechanisms of P retention. The results indirectly confirm the hypothesis of ligand exchange of solution P with organic complexes held on allophanic surfaces. The organic C release, however, is not specifically related to either the fast or the slow P retention phase. The shift in the controlling P retention reaction associated with a change from the fast to the slow P retention phase is clearly indicated by an abrupt change of the pH of the eluent. This shift, in previous studies identified graphically by a change in slope of the P sorption isotherm, can be identified directly by measuring the pH of the matrix.}, number={1}, journal={EUROPEAN JOURNAL OF SOIL SCIENCE}, author={Beck, MA and Robarge, WP and Buol, SW}, year={1999}, month={Mar}, pages={157–164} }
 @article{duffera_robarge_1999, title={Soil characteristics and management effects on phosphorus sorption by highland plateau soils of Ethiopia}, volume={63}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj1999.6351455x}, abstractNote={Differences in crop and fertilizer management are known to influence P retention by soils. An experiment was conducted to study the effect of soil characteristics and management practices on P sorptoin behavior of the highland plateau soils of Ethiopia. Surface samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers' fields, research station farms, and from non‐cultivated‐non‐fertilized areas. Phosphorus sorption data were obtained by equilibrating 3‐g soil samples in 30 mL of 0.01 M CaCl2 containing various amounts of KH2PO4 Inorganic P fractions were determined by the Hedley P fractionation scheme. There was little variation in P sorption among Vertisol samples of alluvial origin as a result of cultivation‐fertilization practices. For soils of volcanic origin (Vertisol2 and Andisols), and the Alfisol, samples collected from farmers' fields sorbed more P than the non‐cultivated and research station samples. Least amounts of applied P sorbed by the non‐cultivated Andisol samples reflect the relatively large amounts of resin extractable P initially present in these soils and demonstrate that labile P initially present in the soil can influence subsequent P sorption. Stepwise regression analysis of the P sorption data showed that resin P accounts for 81% of the variation in P sorption at 0.2 mg P L−1 in solution. The highest amount of P was sorbed by samples collected from farmers' fields and was mainly due to the practice of continuous cropping with minimal P fertilization, which depletes labile P, and therefore requires higher levels of P fertilization for optimum crop yield.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Duffera, M and Robarge, WP}, year={1999}, pages={1455–1462} }
 @article{aneja_roelle_robarge_1998, title={Characterization of biogenic nitric oxide source strength in the southeast United States}, volume={102}, ISSN={["0269-7491"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032446054&partnerID=MN8TOARS}, DOI={10.1016/S0269-7491(98)80035-3}, abstractNote={Emissions of nitric oxide (NO) were measured during the summer of 1995 from 4 crops, located at three different sites throughout North Carolina. These sites were chosen to represent major physiographic regions of the Southeast US, in an effort to compare fluxes from different agriculturally managed soils. Emission rates were determined using a dynamic flow-through chamber system. In order to understand the NO flux from the different soil and crop types, measurements were made on corn and soybean crops in the coastal region, tobacco in the Piedmont region, and corn in the upper Piedmont region of North Carolina. Average NO fluxes were 5.5 f 2.2 ng N me2 s-‘, 20.7 + 19.2 ng N me2 s-‘, 4.1 + 1.4 ng N m-2s-1, and 8.5 2 4.9 ng N me2 s-l respectively for corn and soybean in the coastal region, tobacco in the Piedmont region, and corn in the upper Piedmont region. We were only able to detect an exponential dependence of NO flux on soil temperature at two of the locations. Tbe composite data of all the research sites revealed a general trend of increasing NO flux with soil water content or increasing extractable nitrogen in the soil, however, the day to day variations within each site did not reveal the same trends. We feel that acquisition of a soil NO flux data set in this fashion, which consists of observations collected over different points in both space and time, makes attempts to model soil NO flux in terms of different soil parameters difficult.}, number={SUPPL. 1}, journal={ENVIRONMENTAL POLLUTION}, author={Aneja, VP and Roelle, PA and Robarge, WP}, year={1998}, pages={211–218} }
 @article{kretzschmar_robarge_amoozegar_vepraskas_1997, title={Biotite alteration to halloysite and kaolinite in soil-saprolite profiles developed from mica schist and granite gneiss}, volume={75}, ISSN={["0016-7061"]}, DOI={10.1016/S0016-7061(96)00089-4}, abstractNote={The chemical weathering of biotite and associated formation of secondary minerals has important implications for the genesis, mineralogy, chemical properties, and physical properties of soils and saprolites developed from biotite-rich parent rocks. In this study, we used a combination of X-ray diffraction, micromorphological, and scanning electron microscopy techniques to investigate biotite weathering in two soil-saprolite profiles (Typic Kanhapludults) developed from granite gneiss and mica schist in the Piedmont region of North Carolina, USA. In both profiles, sand-sized biotite grains appeared to be transformed directly into kaolinized pseudomorphs of biotite without going through a detectable vermiculite or interstratified biotite-vermiculite intermediate weathering stage. Minerals with biotite-vermiculite mixed layers were only detected in small amounts in the clay- and silt-sized fractions of the saprolite. Weathering sand-sized biotite grains exhibited expanded edges, exfoliation, and cleavage along (001) planes. In the saprolite developed from granite gneiss, kaolin intergrowths within weathering biotite grains were observed. The edges of weathering biotite grains were densely covered with tubular halloysite, suggesting a complex transformation of biotite to halloysite. Halloysite was the dominant clay mineral in the saprolite, but the halloysite content in the clay fractions diminished towards the soil surface.}, number={3-4}, journal={GEODERMA}, author={Kretzschmar, R and Robarge, WP and Amoozegar, A and Vepraskas, MJ}, year={1997}, month={Feb}, pages={155–170} }
 @article{aneja_roelle_robarge_1997, title={Contribution of biogenic nitric oxide in urban ozone: Raleigh, NC, as a case study}, volume={31}, ISSN={["1352-2310"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0030616154&partnerID=MN8TOARS}, DOI={10.1016/S1352-2310(96)00282-8}, abstractNote={Anthropogenic emissions from industrial and automotive sources within the confines of the city of Raleigh, NC have been documented by the North Carolina Department of Environment, Health and Natural Resources, Division of Environmental Management, but no direct biogenic emissions of nitric oxide (NO) from soils has yet been measured. In this study, emissions of NO were measured in Raleigh, NC, and its surrounding suburbs, in an attempt to determine the portion of the total NOx ( = NO + NO2) budget which can be attributed to biogenic sources. Residential and commercial lawns, and golf courses receiving normal fertilizer applications were chosen as the primary biogenic source of NO. Soil NO fluxes were measured using a dynamic chamber technique from 11 sites and ranged in value (hourly averages calculated from 15 min readings) from 1.24 to 23.7 ng N m−2 s−1. These hour averages were then combined with estimates of lawn acreage within the city proper, and in the surrounding suburbs, in order to develop a budget for giogenic NO emissions in Raleigh. This budget was then compared to the budget used in the Environmental Protection Agency's (EPA) Regional Oxidant Model (ROM) for photochemical modeling. Results from this comparison suggest that less than 1 % of the total NOx budget for Raleigh, NC is emitted by natural processes, and that approximately 1.2% of the nitrogen applied as fertilizer is lost via soil NO emissions. Thus, the effects of biogenic NO may be neglected in the development of a reliable plan for reducing ozone in the urban atmosphere.}, number={10}, journal={ATMOSPHERIC ENVIRONMENT}, author={Aneja, VP and Roelle, P and Robarge, WP}, year={1997}, month={May}, pages={1531–1537} }
 @inproceedings{wang_hesterberg_zhou_sayers_robarge_1997, title={Extended x-ray absorption fine structure study of mercury speciation in a flood plain soil}, number={1997}, booktitle={Contaminated soils: 3rd International Conference on the Biogeochemistry of Trace Elements, Paris (France), May 15-19, 1995}, publisher={Paris: INRA Editions}, author={Wang, Z. and Hesterberg, D. and Zhou, W. and Sayers, D. E. and Robarge, W. P.}, year={1997} }
 @article{aneja_holbrook_robarge_1997, title={Nitrogen oxide flux from an agricultural soil during winter fallow in the upper coastal plain of North Carolina, USA}, volume={47}, ISSN={["2162-2906"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031194163&partnerID=MN8TOARS}, DOI={10.1080/10473289.1997.10463933}, abstractNote={Abstract Incorporation of the remaining crop residue, including the root system, of grain (soybean and corn) and fiber (cotton) crops into the soil following harvest is a common agricultural practice. The crop residue represents a substantial portion of nitrogen initially applied as fertilizer, and thus is a potential source of nitrogen for NO emissions during the winter fallow period. Fluxes of NO and NO2 were measured from fallow fields from February 7 to March 23, 1994, using a dynamic chamber technique (ambient air as the carrier gas). Average NO flux rates, as a function of previous crop residue, were 9.2 (range –4.2 to 76) ng–N m–2 s–1 for soybean, 6.1 (range –11.7 to 110) ng–N m–2 s–1 for cotton, and 4.7 (range –0.2 to 40) ng–N m–2 s–1 for corn. Maximum NO fluxes were observed in mid–morning when soil temperatures were lowest. Minimum NO flux occurred after mid–afternoon when soil temperature reached a maximum. The decrease in NO flux with increase in soil temperature (5 cm depth) reflected the exi...}, number={7}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Aneja, VP and Holbrook, BD and Robarge, WP}, year={1997}, month={Jul}, pages={800–805} }
 @article{li_amoozegar_robarge_buol_1997, title={Water movement and solute transport through saprolite}, volume={61}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj1997.03615995006100060027x}, abstractNote={AbstractMany soils are underlain by saprolite. The purpose of this study was to assess the potential for preferential movement of pollutants through one soil and two saprolites in the Piedmont region of North Carolina. At one site (Site 1), two 100 by 100 by 100 cm intact blocks were isolated in situ in the Bt horizon and underlying saprolite, and a solution containing KBr, NH4NO3, a blue dye, and a red dye was applied to the top of each block. At a second location (Site 2), a 120 by 120 by 100 cm intact block of saprolite was similarly prepared. Acid red dye powder (5 g) was placed in four small holes (3 cm deep) bored into the surface of the block, and the block was leached with a solution containing only KBr and NH4NO3. After drainage, each block was dissected layer by layer (5 or 10 cm thick), and the middle 80 by 80 by 100 cm volume was divided into 768 samples and analyzed for K+, Br‐, NH+4, and NO‐3, as well as dye content. The visible patterns of the dyes, and extracted solute concentrations, at Site 1 indicated that preferential movement was more pronounced in the Bt horizon than in the saprolite. At Site 2, the red dye and solutes moved vertically with little lateral deviation. Our results suggest that vertical water movement in the two saprolites occurs mainly through matrix pores with little preferential movement via the visible features inherited from respective parent rocks.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Li, K and Amoozegar, A and Robarge, WP and Buol, SW}, year={1997}, pages={1738–1745} }
 @article{hesterberg_sayers_zhou_plummer_robarge_1997, title={X-ray absorption spectroscopy of lead and zinc speciation in a contaminated groundwater aquifer}, volume={31}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031260138&partnerID=MN8TOARS}, DOI={10.1021/es970077w}, abstractNote={The formation of insoluble metal sulfides in the environment may reduce the mobility and bioavailability of heavy metal contaminants and potentially eliminate the need for ex situ remediation of certain hazardous waste sites. To assist in assessing remediation strategies for the Bypass 601 Superfund site, groundwater aquifer samples were analyzed using synchrotron X-ray absorption spectroscopy (XAS) to determine whether lead and zinc sulfides were dominant mineral phases. Moist aquifer solids contained between 150 and 1800 mg of Pb/kg and between 100 and 250 mg of Zn/kg. Lead sulfide was not dominant in any of the samples analyzed, including one sample collected from a well in a flood plain that contained 70% of zinc bonded to sulfur, probably as ZnS. This portion of the aquifer had apparently been under reducing conditions. In all other samples, first-shell bonding of Pb and Zn was predominantly to oxygen. Data indicated that PbO, PbCO3, PbSO4, and ZnO were not dominant metal species. The XAS analyses sh...}, number={10}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Hesterberg, D and Sayers, DE and Zhou, WQ and Plummer, GM and Robarge, WP}, year={1997}, month={Oct}, pages={2840–2846} }
 @article{hesterberg_sayers_zhou_robarge_plummer_1997, title={XAFS Characterization of Copper in Model Aqueous Systems of Humic Acid and Illite}, volume={7}, ISSN={1155-4339}, url={http://dx.doi.org/10.1051/jp4:1997253}, DOI={10.1051/jp4:1997253}, abstractNote={Adsorption of heavy metals at mineral surfaces and complexation with reactive organic-matter functional groups are important processes regulating the solubility and fate of soil contaminants. To determine the nature of Cu(II) bonding in complex clay-organic systems, XAFS analyses were conducted on aqueous suspensions containing Cu(II) in various forms: (i) complexed with soil humic acid (HA) at various HA:Cu ratios, (ii) bound to illite, or (iii) bound in a mixture of illite and HA. Spectral features for Cu bound to HA did not depend significantly on the HA:Cu ratio, and average first-shell Cu-O bond lengths were consistently shorter than for the Cu-illite systems. In the mixed clay-organic suspension, Cu bonding was more characteristic to that of Cu bound with HA.}, number={C2}, journal={Le Journal de Physique IV}, publisher={EDP Sciences}, author={Hesterberg, D. and Sayers, D. E. and Zhou, W. and Robarge, W. P. and Plummer, G. M.}, year={1997}, month={Apr}, pages={C2–833-C2–834} }
 @article{sayers_hesterberg_zhou_robarge_plummer_1997, title={XAFS characterization of copper contamination in the unsaturated and saturated zones of a soil profile}, volume={7}, ISSN={["1155-4339"]}, DOI={10.1051/jp4:1997252}, abstractNote={The fate of heavy-metal contaminants in the environment, and the design and success of remediation strategies at hazardous waste sites depend on the chemical speciation of the contaminants. The objective of this study was to determine the molecular-scale chemical form (species) of heavy metals in different zones of a contaminated soil having a shallow ground water table. Copper in the unsaturated surface horizon and the water-saturated and partially-saturated subsurface horizons of a disturbed soil from the lower eastern coastal plain of North Carolina was characterized using XAFS spectroscopy. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) data showed that the dominant form of Cu(II) bonding ranged from Cu-S in the deeper soil zones to Cu-O in the shallowest zone. The results suggest that the surface and subsurface horizons will respond differently to remediation treatments.}, number={C2}, journal={JOURNAL DE PHYSIQUE IV}, author={Sayers, DE and Hesterberg, D and Zhou, W and Robarge, WP and Plummer, GM}, year={1997}, month={Apr}, pages={831–832} }
 @misc{robarge_johnson_1992, title={THE EFFECTS OF ACIDIC DEPOSITION ON FORESTED SOILS}, volume={47}, ISSN={["2213-6789"]}, DOI={10.1016/S0065-2113(08)60488-5}, abstractNote={This chapter provides an overview of soil acidification that is one of the effects of acidic deposition on forest ecosystems. It also provides a brief synopsis of the dominant physical and chemical processes in forest ecosystems that interact with, modify, and respond to acidic inputs. The degree of interaction between acidic deposition and the forest canopy is illustrated. The chapter presents several case histories of soil change in regions where acid deposition may be causal and in regions where it is not. A set of recommendations is outlined, concerning areas for future research that are needed to be characterized properly and models for the effects of acidic deposition on forest soils are developed. Several hypotheses are proposed as the basis for future research on potential atmosphere–rhizosphere interactions that include above-ground physiology, nutrient uptake, heavy metal uptake, aluminum uptake, or microbes essential for nutrient absorption and changes in the forest ecosystem due to atmospheric deposition that alters rhizosphere regulation of root pathogens and soil saprophyte ecology.}, journal={ADVANCES IN AGRONOMY}, author={ROBARGE, WP and JOHNSON, DW}, year={1992}, pages={1–83} }
 @inproceedings{bruck_robarge_mcdaniel_1989, title={Decline in the boreal montane ecosystems of the Southern Appalachian Mountains - USA, the air pollution factor}, volume={48}, DOI={10.1007/bf00282376}, number={1-2}, booktitle={Proceedings of the 4th International Congress on Ecology and Ecosystem Stability}, publisher={ISEEQS Press}, author={Bruck, R. I. and Robarge, W. P. and McDaniel, A.}, year={1989}, pages={259–268} }
 @article{meier_robarge_bruck_grand_1989, title={EFFECTS OF SIMULATED RAIN ACIDITY ON ECTOMYCORRHIZAE OF RED SPRUCE SEEDLINGS POTTED IN NATURAL SOIL}, volume={59}, ISSN={["0269-7491"]}, DOI={10.1016/0269-7491(89)90158-9}, abstractNote={Formation of ectomycorrhizae of red spruce (Picea rubens) grown in natural soil was measured after seedlings were exposed to 25 or 50 applications of simulated rain of pH 5·5, 3·5 or 2·5. Ectomycorrhizae were quantified as the total number of ectomycorrhizal tips per centimeter, and as the number of ectomycorrhizal tips for each morphotype and for Cenococcum geophilum. Rain solutions were applied to the soil alone, to foliage and stem alone, or to entire potted seedlings. Final soil pH was linearly related to rain solution acidity. Lower base saturation, calcium and zinc content, and higher exchangeable acidity were observed after pH 2·5 treatments if the soil was exposed. Rain solutions and the subsequent changes in soil characteristics did not affect the total numbers of ectomycorrhizal tips. Four morphotypes of ectomycorrhizae observed for these seedlings were unaffected by simulated rain. However, the numbers of ectomycorrhizal tips formed by C. geophilum tended to increase with rain solution acidity after 50 applications. Method of rain deposition did not affect ectomycorrhizae, suggesting both plant and soil mediated responses may favor certain mycobionts. The results of this study indicate that short-term acidic deposition does not induce significant changes in the frequency of ectomycorrhizae, but higher numbers of C. geophilum tips suggest there may be changes in the relative occurrence of specific morphotypes of fungus species.}, number={4}, journal={ENVIRONMENTAL POLLUTION}, author={MEIER, S and ROBARGE, WP and BRUCK, RI and GRAND, LF}, year={1989}, pages={315–324} }
 @article{robarge_pye_bruck_1989, title={FOLIAR ELEMENTAL COMPOSITION OF SPRUCE-FIR IN THE SOUTHERN BLUE RIDGE PROVINCE}, volume={114}, ISSN={["1573-5036"]}, DOI={10.1007/BF02203077}, number={1}, journal={PLANT AND SOIL}, author={ROBARGE, WP and PYE, JM and BRUCK, RI}, year={1989}, month={Feb}, pages={19–34} }
 @inproceedings{bruck_robarge_mcdaniel_1989, title={Forest decline in the Southern Appalachian Mountains: Research and observations, 1983-1989}, ISBN={3923704054}, booktitle={Proceedings of the International Congress on Forest Decline Research: State of knowledge and perspectives}, publisher={Karlsruhe, Germany: Kernforschungszentrum Karlsruhe GmbH}, author={Bruck, R. I. and Robarge, W. P. and McDaniel, A.}, year={1989}, pages={367–393} }
 @inproceedings{bruck_bradow_brockhaus_cure_khorram_mcdaniel_modena_robarge_smithson_1989, title={Observations of forest decline in the boreal montane ecosystems of Mt. Mitchell, N.C.}, booktitle={Proceedings of the U.S.-F.R.G. Symposium on Forest Decline, Burlington, VT, Oct. 19-24, 1987 (USDA Forest Service Technical publication #120)}, publisher={USDA Forest Service}, author={Bruck, R. I. and Bradow, R. and Brockhaus, J. and Cure, B. and Khorram, S. and McDaniel, A. and Modena, S. and Robarge, W. and Smithson, P.}, year={1989}, pages={97–107} }
 @inproceedings{robarge_bruck_cowling_1989, title={Throughfall and stemflow measurements at Mt. Mitchell, N.C. during the summer of 1986}, booktitle={Proceedings of the U.S.-F.R.G. Symposium on Forest Decline (Technical publication #120)}, publisher={USDA Forest Service}, author={Robarge, W. P. and Bruck, R. I. and Cowling, E. B.}, year={1989}, pages={111–117} }
 @article{bruck_robarge_1988, title={Change in the structure of the boreal montane ecosystem of Mt. Mitchell, North Carolina}, volume={18}, DOI={10.1111/j.1439-0329.1988.tb00223.x}, abstractNote={AbstractSurveys were undertaken on Mt. Mitchell, N. C. (USA) from Spring 1984 through 1987 to determine the extent and rate of decline and mortality of red spruce and Fraser fir ecosystems. Data indicate that regardless of cause and effect mechanisms the physical structure and integrity of the boreal montane forest has greatly deteriorated over the past 4 years. Along ridges, and particularly on west facing aspects greater than 80% of all mature stands are dead. No definitive conclusions can be made concerning etiological agents; however, current hypotheses include biotic factors, climatic abberations, and/or the acute or chronic stress from anthropogenic pollutants.}, journal={European Journal of Forest Pathology}, author={Bruck, R. I. and Robarge, W. P.}, year={1988}, pages={357–366} }
 @inproceedings{robarge_smithson_modena_bruck_cowling_1987, title={Study of cloud originated stemflow and throughfall collections from red spruce and Fraser fir trees at Mt. Mitchell, NC}, booktitle={American Chemical Society Annual Meeting}, author={Robarge, W. P. and Smithson, P. C. and Modena, S. A. and Bruck, R. I. and Cowling, E. B.}, year={1987}, pages={171–184} }
 @inproceedings{bruck_robarge_1987, title={Three-year survey of boreal montane forest decline in the Southern Appalachian Mountains}, booktitle={Proceedings of The National Atmospheric Deposition Program Terrestrial Effects Peer Review}, publisher={Washington, DC: National Acid Precipitation Assessment Program}, author={Bruck, R. I. and Robarge, W. P.}, year={1987}, pages={101–113} }
 @article{bruck_robarge_1985, title={Decline of boreal montane ecosystems in the Southern Appalachian Mountains}, volume={29}, journal={Water, Air, and Soil Pollution}, author={Bruck, R. I. and Robarge, W. P.}, year={1985}, pages={1191} }
 @book{bruck_robarge_1985, title={Final report: Epidemiology of boreal montane forest decline in the Southern Appalachian Mountains}, institution={U. S. Environmental Protection Agency}, author={Bruck, R. I. and Robarge, W. P.}, year={1985} }
 @inproceedings{bruck_robarge_1985, title={Forest decline in the Southern Appalachian Mountains}, booktitle={Proceedings of the International Symposium on Acidic Precipitation}, author={Bruck, R. I. and Robarge, W. P.}, year={1985}, pages={279–286} }
 @book{bruck_robarge_reynolds_rebertus_pye_haley_1984, title={Observations of boreal montane decline in the Southern Appalachian Mountains: Soil and vegetation studies (NAPAP peer review document)}, institution={U.S. Environmental Protection Agency}, author={Bruck, R. I. and Robarge, W. P. and Reynolds, K. M. and Rebertus, R. and Pye, J. and Haley, K.}, year={1984} }
 @article{robarge_edwards_johnson_1983, title={WATER AND WASTEWATER ANALYSIS FOR NITRATE VIA NITRATION OF SALICYLIC-ACID}, volume={14}, ISSN={["0010-3624"]}, DOI={10.1080/00103628309367444}, abstractNote={Abstract A method is presented which allows rapid nitrate analyses of water and waste water samples and soil extracts. The linear working range is typically 0.5–30 mg NO− 3‐N/liter and duplicate analysis of samples and standards routinely produces confidence limits for the regression estimate of ‐ ±0.1 mg NO− 3‐N/liter at the 95% confidence level. Nitrite, formaldehyde and soluble Iron, as Fe3+, cause a positive Interference, while chloride causes a negative interference. The extent of the Interference is a function of the amount of nitrate present.}, number={12}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={ROBARGE, WP and EDWARDS, A and JOHNSON, B}, year={1983}, pages={1207–1215} }