@article{moursi_youssef_poole_castro-bolinaga_chescheir_richardson_2023, title={Drainage water recycling reduced nitrogen, phosphorus, and sediment losses from a drained agricultural field in eastern North Carolina, USA}, volume={279}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2023.108179}, abstractNote={An experimental study was conducted to evaluate the effect of drainage water recycling (DWR) on reducing nitrogen (N), phosphorus (P), and sediment losses from agricultural fields to downstream surface water bodies. The two-year study (May 2019-April 2021) was conducted at an agricultural field in eastern North Carolina, U.S.A. A reservoir existed at the site was used to store subsurface drainage and surface runoff water during wet periods and provide supplemental irrigation during dry periods of the crop growing season. On average, the reservoir retained 14% of received inflow, with a higher flow reduction in the dry year (2019–2020; 29%) than the wet year (2020–2021; 8%). The hydraulic retention time (HRT) for the reservoir was 33.8 days for the dry year and 12.4 days for the wet year. The reservoir significantly reduced the loadings of N by 47%, P by 30% and sediment by 87%. Nitrogen load reduction was primarily driven by nitrate assimilation, the dominant form of N in the reservoir. Phosphorus load reduction was attributed to Orthophosphate assimilation as the reservoir released more particulate P than received. Reductions in both water flow and species concentration contributed to nutrient load reductions. Results suggested the removal efficiency of the reservoir would be highest during the summer and early fall months when the reservoir has a smaller water volume (due to irrigation), longer HRT, and warmer temperature. This study clearly demonstrated the potential of DWR for significantly reducing N, P, and sediment losses from agricultural land to receiving surface water. Further research is needed to investigate the physical, chemical, and biological processes that occur in the storage reservoir and affect the fate and transport of nutrients and sediment. The understanding of these processes will enable optimizing the treatment efficiency of DWR, which maximizes the system’s benefits and reduces construction cost.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Moursi, Hossam and Youssef, Mohamed A. and Poole, Chad A. and Castro-Bolinaga, Celso F. and Chescheir, George M. and Richardson, Robert J.}, year={2023}, month={Apr} }
 @article{youssef_strock_bagheri_reinhart_abendroth_chighladze_ghane_shedekar_fausey_frankenberger_et al._2023, title={Impact of controlled drainage on corn yield under varying precipitation patterns: A synthesis of studies across the US Midwest and Southeast}, volume={275}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2022.107993}, abstractNote={Controlled drainage (CD) is a valuable management practice for reducing drainage volume and nutrient loss, but its impact on corn (Zea mays L.) production is not completely understood. The objectives of this study were to investigate the regional effect of CD on corn grain yield compared to free drainage (FD), investigate the factors influencing corn yield response to CD, provide management recommendations for optimizing corn yield under CD, and identify future research needs for corn production on poorly drained soils with subsurface drainage systems. This synthesis included data collected from 13 field sites where corn was planted under both FD and CD in six U.S. Midwestern states and North Carolina totaling 55 site-years of data from 2006 to 2017. On average, there was no statistically significant difference in corn grain yield between CD (10.62 Mg/ha) and FD (10.53 Mg ha−1). However, 42% of the dataset indicated that CD either increased or decreased corn yield by 4% or more compared to FD. Further analysis was conducted on this subset of data in order to evaluate underlying factors (i.e., weather conditions during the season, soil type, and drainage system design and management) influencing corn yield response to CD. Results of this analysis showed that CD was effective in alleviating plant stress caused by mild to moderate drought conditions and subsequently increased corn grain yield by 4–14% in 12 site-years. In contrast, CD reduced corn grain yield by 4–10% during wet growing seasons (6 site-years). Variability in growing season precipitation has been identified as a key factor influencing corn grain yield under CD, and more active management or CD system automation is recommended. General recommendations are provided for managing manually operated CD systems in the U.S. Midwest to improve growing season water management and corn yield. Additional research to develop technologically advanced water management systems for crop production on poorly drained soils is needed in order to adapt to changing weather patterns.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Youssef, Mohamed A. and Strock, Jeffrey and Bagheri, Ehsan and Reinhart, Benjamin D. and Abendroth, Lori J. and Chighladze, Giorgi and Ghane, Ehsan and Shedekar, Vinayak and Fausey, Norman R. and Frankenberger, Jane R. and et al.}, year={2023}, month={Jan} }
 @article{moursi_youssef_chescheir_2022, title={Development and application of DRAINMOD model for simulating crop yield and water conservation benefits of drainage water recycling}, volume={266}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2022.107592}, abstractNote={Drainage water recycling (DWR) is an emerging practice that has the potential to increase crop yield and improve water quality. DWR involves capturing and storing subsurface drainage water and surface runoff in ponds or reservoirs, and using this water for supplemental irrigation during dry periods of the growing season. The main objective of this study was to enhance DRAINMOD model to simulate the hydrology and crop yield of DWR systems. The expanded model; named DRAINMOD-DWR, has a new module that conducts a water balance of the storage reservoir and simulates the interaction between the reservoir and the field, irrigated from and/or draining into the reservoir. The model predicts the long-term performance of DWR as affected by weather conditions, soil type, crop rotation, reservoir size, and irrigation and drainage management. Three performance metrics were defined based on model predictions to quantify irrigation, crop yield, and water capture benefits of DWR. To demonstrate the new features of the model, uncalibrated DRAINMOD-DWR was applied to a hypothetical DWR system with continuous corn using a 50-yr (1970–2019) weather record in Eastern North Carolina, U.S. Different reservoir sizes were simulated to demonstrate how the model can predict the effect of storage capacity on the system’s performance. The model predicted that a 3.0-m deep reservoir with a surface area of 4% of the field area would optimize corn yield for the simulated conditions. The model application clearly demonstrated the DRAINMOD-DWR model’s capability of optimizing the DWR system design to avoid under-sizing or over-sizing the storage reservoir, which reduces system’s performance and increases implementation cost. Research is needed to test DRAINMOD-DWR using field measured data, and to develop routines for simulating the fate and transport of nutrients and sediment in the storage reservoir, which would enable the model to predict the water quality benefits of DWR.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Moursi, Hossam and Youssef, Mohamed A. and Chescheir, George M.}, year={2022}, month={May} }
 @article{helmers_abendroth_reinhart_chighladze_pease_bowling_youssef_ghane_ahiablame_brown_et al._2022, title={Impact of controlled drainage on subsurface drain flow and nitrate load: A synthesis of studies across the US Midwest and Southeast}, volume={259}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2021.107265}, abstractNote={Controlled drainage (CD), sometimes called drainage water management, is a practice whereby the drainage system outflow is managed during specific periods to retain more water in the field. Although CD has been shown to reduce downstream nitrate-N (NO3--N) load, seasonal patterns have been less consistent which can potentially impact the effectiveness of conservation practices. The main objective of this study was to assess the regional and seasonal impact of conventional free drainage (FD) and CD on drainage flow and nitrate-N load. Using experimental data from ongoing and historical CD experiments across the Corn Belt and in North Carolina, we evaluated subsurface drain flow, nitrate-N load, and performance of CD systems. Across the data set and regions, there was little difference in annual flow from FD conditions. Seasonally, more northern and western sites experienced a greater percentage of the annual flow occurring in the spring. There was no nitrate-N concentration reduction with CD. Flow and nitrate-N load reductions with CD did not vary by plant hardiness zone across the region, but the season with the greatest reduction did shift from winter to spring moving north and west in the study area. Absolute flow reductions (in mm) were similar regardless of precipitation category. Consequently, the percent reduction was lower as the amount of precipitation (category) increased. Overall, this analysis found CD to be an effective practice for reducing drain flow and nitrate-N loading directly delivered by the drains to downstream water bodies across the region.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Helmers, M. J. and Abendroth, L. and Reinhart, B. and Chighladze, G. and Pease, L. and Bowling, L. and Youssef, M. and Ghane, E. and Ahiablame, L. and Brown, L. and et al.}, year={2022}, month={Jan} }
 @article{abendroth_chighladze_frankenberger_bowling_helmers_herzmann_jia_kjaersgaard_pease_reinhart_et al._2022, title={Paired field and water measurements from drainage management practices in row-crop agriculture}, volume={9}, ISSN={["2052-4463"]}, DOI={10.1038/s41597-022-01358-7}, abstractNote={Abstract}, number={1}, journal={SCIENTIFIC DATA}, author={Abendroth, L. J. and Chighladze, G. and Frankenberger, J. R. and Bowling, L. C. and Helmers, M. J. and Herzmann, D. E. and Jia, X. and Kjaersgaard, J. and Pease, L. A. and Reinhart, B. D. and et al.}, year={2022}, month={Jun} }
 @article{liu_tian_youssef_birgand_chescheir_2022, title={Patterns of long-term variations of nitrate concentration - Stream discharge relationships for a drained agricultural watershed in Mid-western USA}, volume={614}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2022.128479}, abstractNote={Nitrate Concentration–discharge (C-Q) relationships have been used to infer nitrate sources, storage, reactions, and transport in watersheds, and to reveal key processes that control runoff chemistry. Yet, studies on long-term nitrate C-Q relationships are limited due to scarce high frequency (e.g., daily) concentration data. In this paper, using a long-term high-frequency dataset (1976–2019) comprising stream flow and nitrate concentrations, we quantitatively analyzed the long-term variations of event-scale hysteresis patterns (quantified by hysteresis index, HI, and flushing index, FI) to infer the leaching mechanisms of nitrate in an artificially drained agricultural watershed in Mid-western U.S. Our results revealed that most events exhibited anti-clockwise behaviors (HI < 0), regardless of whether nitrate was flushed or diluted during events. This means that water with high levels of nitrate-N reaches the stream network slower than water with lower nitrate concentrations. Long-term mean FI was close to zero but had strong seasonal patterns with dilution patterns observed during Winter and Summer, and flushing patterns during late Spring and Fall. The consistently negative HI values regardless of the FI value gave a strong indication of the preponderant role of the near-drain zone that usually exhibits accelerated leaching and less accumulation of nitrate in the soil profile in these drained agricultural watersheds. Both HI and FI depicted strong but opposite seasonality because of weather patterns and agricultural activities, particularly N fertilization. Overall, our findings suggest a little evidence of the role of deep groundwater and instead a strong evidence of the role of subsurface drainage as the primary pathway for nitrate transport in drained agricultural watersheds. Therefore, artificial drainage could dampen N legacy caused by the historically intensive N fertilization in drained agricultural landscapes.}, journal={JOURNAL OF HYDROLOGY}, author={Liu, Wenlong and Tian, Shiying and Youssef, Mohamed A. and Birgand, Francois P. and Chescheir, George M.}, year={2022}, month={Nov} }
 @article{youssef_liu_chescheir_skaggs_negm_2021, title={DRAINMOD modeling framework for simulating controlled drainage effect on lateral seepage from artificially drained fields}, volume={254}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2021.106944}, abstractNote={We demonstrated a DRAINMOD modeling framework to predict controlled drainage (CD) effect on the fate of water in artificially drained agricultural fields, which is key for determining the water quality benefits of the practice. To demonstrate this modeling framework, DRAINMOD simulated the hydrology of a subsurface drained grass field in Eastern North Carolina, U.S. under both free drainage (FD) and CD. Three scenarios were simulated for each water management: no lateral seepage (LS) and LS with constant and dynamic hydraulic head (Hr). For each scenario, predicted water table depth (WTD) and subsurface drainage were compared to observed values using Mean Absolute Error, Nash-Sutcliffe Efficiency, and Normalized Percent Error. Predicted water balance components for different scenarios were also investigated. Results clearly showed that LS was a significant component of the water balance for CD. Model predictions showed that 96% of the reduction in subsurface drainage due to CD could be attributed to LS (33.5 cm yr−1). The large values of LS predicted by the model were attributed to the presence of a permeable sandy layer in the soil profile, the shallow management depth of the drain outlet, and the small size of the experimental field plots. Agreement between predicted and observed WTD and subsurface drainage ranged from acceptable to excellent for FD with and without considering LS. In contrast, DRAINMOD simulations for CD yielded acceptable predictions only for the scenario considering LS with dynamic Hr. This study demonstrated the power of process-based simulation models, such as DRAINMOD, for interpreting and explaining data of experimental studies and underscored the importance of using a proper model calibration strategy for yielding reliable predictions. This study highlights the need for well-coordinated experimental and modeling research to further investigate how seepage affect CD performance for reducing drainage flow and nitrogen losses from artificially drained agricultural fields.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Youssef, Mohamed A. and Liu, Yu and Chescheir, George M. and Skaggs, R. Wayne and Negm, Lamyaa M.}, year={2021}, month={Aug} }
 @article{askar_youssef_vadas_hesterberg_amoozegar_chescheir_skaggs_2021, title={DRAINMOD-P: A MODEL FOR SIMULATING PHOSPHORUS DYNAMICS AND TRANSPORT IN DRAINED AGRICULTURAL LANDS: I. MODEL DEVELOPMENT}, volume={64}, ISSN={["2151-0040"]}, DOI={10.13031/trans.14509}, abstractNote={Highlights}, number={6}, journal={TRANSACTIONS OF THE ASABE}, author={Askar, Manal H. and Youssef, Mohamed A. and Vadas, Peter A. and Hesterberg, Dean L. and Amoozegar, Aziz and Chescheir, George M. and Skaggs, R. Wayne}, year={2021}, pages={1835–1847} }
 @article{askar_youssef_hesterberg_king_amoozegar_skaggs_chescheir_ghane_2021, title={DRAINMOD-P: A MODEL FOR SIMULATING PHOSPHORUS DYNAMICS AND TRANSPORT IN DRAINED AGRICULTURAL LANDS: II. MODEL TESTING}, volume={64}, ISSN={["2151-0040"]}, DOI={10.13031/trans.14510}, abstractNote={Highlights}, number={6}, journal={TRANSACTIONS OF THE ASABE}, author={Askar, Manal H. and Youssef, Mohamed A. and Hesterberg, Dean L. and King, Kevin W. and Amoozegar, Aziz and Skaggs, R. Wayne and Chescheir, George M. and Ghane, Ehsan}, year={2021}, pages={1849–1866} }
 @article{amatya_tian_marion_caldwell_laseter_youssef_grace_chescheir_panda_ouyang_et al._2021, title={Estimates of Precipitation IDF Curves and Design Discharges for Road-Crossing Drainage Structures: Case Study in Four Small Forested Watersheds in the Southeastern US}, volume={26}, ISSN={["1943-5584"]}, DOI={10.1061/(ASCE)HE.1943-5584.0002052}, abstractNote={AbstractWe compared precipitation intensity-duration-frequency (PIDF) curves developed for four small forested watersheds to spatially interpolated estimates from the National Oceanic and Atmospher...}, number={4}, journal={JOURNAL OF HYDROLOGIC ENGINEERING}, author={Amatya, D. M. and Tian, S. and Marion, D. A. and Caldwell, P. and Laseter, S. and Youssef, M. A. and Grace, J. M. and Chescheir, G. M. and Panda, S. and Ouyang, Y. and et al.}, year={2021}, month={Apr} }
 @article{hay_reinhart_frankenberger_helmers_jia_nelson_youssef_2021, title={FRONTIER: DRAINAGE WATER RECYCLING IN THE HUMID REGIONS OF THE US: CHALLENGES AND OPPORTUNITIES}, volume={64}, ISSN={["2151-0040"]}, DOI={10.13031/trans.14207}, abstractNote={Highlights}, number={3}, journal={TRANSACTIONS OF THE ASABE}, author={Hay, Christopher H. and Reinhart, Benjamin D. and Frankenberger, Jane R. and Helmers, Matthew J. and Jia, Xinhua and Nelson, Kelly A. and Youssef, Mohamed A.}, year={2021}, pages={1095–1102} }
 @article{askar_youssef_chescheir_negm_king_hesterberg_amoozegar_skaggs_2020, title={DRAINMOD Simulation of macropore flow at subsurface drained agricultural fields: Model modification and field testing}, volume={242}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2020.106401}, abstractNote={Macropores are critical pathways through which water and pollutants can bypass the soil matrix and be rapidly transported to subsurface drains and freshwater bodies. We modified the DRAINMOD model to simulate macropore flow using a simple approach as part of developing the DRAINMOD-P model to simulate phosphorus dynamics in artificially drained agricultural lands. The Hagen-Poiseuille’s law was used to estimate the flow capacity of macropores. When ponding depths on the soil surface are greater than Kirkham’s depth, water is assumed to flow through macropores directly to tile drains without interaction with the soil matrix. In the modified model, macropore size is adjusted based on wet or dry conditions while connectivity is altered by tillage. The model was tested using a 4-year data set from a subsurface drained field in northwest Ohio. The soils at the field are classified as very poorly drained and are prone to desiccation cracking. The modified model predicted the daily and monthly subsurface drainage with average Nash-Sutcliffe efficiency (NSE) values of 0.48 and 0.59, respectively. The cumulative drainage over the 4-year simulation period was under-predicted by 8%. The new macropore component was able to capture about 75% of 60 peak drainage flow events. However, surface runoff was over-predicted for the entire study period. Annual water budgets using measured data (precipitation, subsurface drainage, and surface runoff) and model predictions (evapotranspiration, vertical seepage, and change in storage) were not balanced with an average annual imbalance of 6.4 cm. The lack of closure in the water balance suggests that errors may have occurred in field measurements, particularly, surface runoff. Overall, incorporating macropore flow into DRAINMOD improved predictions of daily drainage peaks and enabled the model to predict subsurface drainage flux contributed by macropore flow, which is critical for expanding DRAINMOD to simulate phosphorus transport in subsurface drained agricultural land.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Askar, Manal H. and Youssef, Mohamed A. and Chescheir, George M. and Negm, Lamyaa M. and King, Kevin W. and Hesterberg, Dean L. and Amoozegar, Aziz and Skaggs, R. Wayne}, year={2020}, month={Dec} }
 @article{lisenbee_hathaway_negm_youssef_winston_2020, title={Enhanced bioretention cell modeling with DRAINMOD-Urban: Moving from water balances to hydrograph production}, volume={582}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2019.124491}, abstractNote={Bioretention systems have become a leading stormwater control measure for mitigating urban hydrology. Although these systems have performed well in many site-scale field studies, less investigation has been directed toward effectively modeling these systems. This is critical, as modeling of bioretention systems provides an avenue for evaluating their effectiveness prior to devoting time and resources into installation. Many hydrologic models capable of simulating bioretention consist of lumped parameters and simplifications that do not fully account for fundamental hydrologic processes such as soil-water interactions. DRAINMOD has shown promise for obtaining detailed daily water balances within bioretention systems under continuous simulations. One significant advantage of DRAINMOD is that it uses the soil-water characteristic curve to account for fluctuations in soil moisture instead of assuming saturation; however, the model historically only produces daily outputs. For this study, DRAINMOD was modified to develop DRAINMOD-Urban, which allows high temporal resolution inputs and outputs, more closely matching the residence time of runoff in urban systems. DRAINMOD-Urban simulations of a bioretention cell in Ohio, USA, revealed that DRAINMOD-Urban could effectively produce hydrographs with a cumulative Nash-Sutcliffe Efficiency (NSE) of 0.60 for the 12 events that produced drainage over a 7-month monitoring period. Overflow was also modeled by DRAINMOD-Urban, but additional overflow data are necessary to derive conclusions about model effectiveness in predicting this hydrologic component. Input parameters previously calibrated for the DRAINMOD model did not translate well to DRAINMOD-Urban with the top-down approach applied in this study (NSE = 0.31 for drainage and NSE = −1.83 for overflow), but the bottom-up approach showed that parameters calibrated with DRAINMOD-Urban (NSE = 0.60 for drainage and NSE = −0.1 for overflow) could be used in DRAINMOD to obtain reasonable drainage volumes (25.6% error compared to measured values). This study suggests DRAINMOD-Urban is an effective tool for modeling bioretention hydrographs and demonstrates the importance of temporal scale in bioretention modeling by illustrating multiple model calibration approaches. Despite the promising results of this study, additional studies are recommended where validation of the model is performed at more sites, in particular for events with overflow. Further, sensitivity analysis of input parameters and comparison of DRAINMOD-Urban to other commonly used bioretention models would inform future modeling efforts.}, journal={JOURNAL OF HYDROLOGY}, author={Lisenbee, W. and Hathaway, Jon and Negm, L. and Youssef, M. and Winston, R.}, year={2020}, month={Mar} }
 @article{negm_youssef_jaynes_2020, title={Evaluation of DRAINMOD-DSSAT simulated effects of controlled drainage on crop yield, water balance, and water quality for a corn-soybean cropping system in central Iowa (vol 187, pg 57, 2017)}, volume={229}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.105810}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, Lamyaa M. and Youssef, Mohamed A. and Jaynes, Dan B.}, year={2020}, month={Feb} }
 @article{singh_bhattarai_negm_youssef_pittelkow_2020, title={Evaluation of nitrogen loss reduction strategies using DRAINMOD-DSSAT in east-central Illinois}, volume={240}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2020.106322}, abstractNote={Agricultural system modeling has become an effective tool for analyzing and quantifying the effects of varying management practices and environmental conditions on crop production and nutrient export from croplands. The use of such modeling tools provides useful insights in identifying the most effective management practices for enhancing productivity, sustainability, and resiliency of agricultural systems. This study focuses on testing and application of an integrated field-scale process-based model, DRAINMOD-DSSAT, for simulating hydrology, nitrate-nitrogen (NO3-N) loss, and crop growth and yield responses in artificially drained croplands. The tested model was used to evaluate the effects of different N fertilizer application rates and timings in both conventional and controlled drainage conditions on crop yield and NO3-N losses in a poorly drained Drummer-Flanagan soil in east-central Illinois. The model was calibrated and validated for a corn [Zea Mays L.] – soybean [Glycine Max (L.)] rotation using 7 years (1992–1998) of field-measured tile drainage, crop yield, and NO3-N data. The graphical and statistical evaluations indicated very good model performance. Specifically, monthly tile drainage flow was predicted with modeling efficiency (NSE), index of agreement (d), and mean absolute error (MAE) of 0.85, 0.96, and 0.69 cm, respectively. Monthly NO3-N losses were predicted with NSE, d, and MAE of 0.82, 0.95, and 1.16 kg N ha−1, respectively. Corn and soybean yields were predicted with an absolute percent error (PE) of 1.84 and 12.07, respectively. The long-term model simulation results indicated that split N application of 50 % during spring-pre plant (S) and 50 % during side-dressing (SD) could increase crop yield and reduce N leaching losses compared to other tested N application methods: spring (S) only, fall-spring split (F-S), and fall-spring-side-dressing (F-S-SD). Further, applying 10 % and 20 % reduced N rates (194 kg N ha−1 and 174 kg N ha−1, respectively) in combination with S-SD split application in controlled drainage (CD) condition could reduce N leaching losses by 30 % and 33 %, respectively compared to the conventional application method. This study explored the effects of N fertilizer management on crop yield and nitrogen losses under two drainage conditions, and underscored the importance of N fertilizer application rates and timings for achieving yield goals while minimizing nitrogen export from drained agricultural fields. The results of the model simulations will be useful for stakeholders and policy makers while making decisions regarding promotion and adoption of best management practices for drained agricultural landscapes.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Singh, Shailendra and Bhattarai, Rabin and Negm, Lamyaa M. and Youssef, Mohamed A. and Pittelkow, Cameron M.}, year={2020}, month={Oct} }
 @article{liu_youssef_birgand_chescheir_tian_maxwell_2020, title={Processes and mechanisms controlling nitrate dynamics in an artificially drained field: Insights from high-frequency water quality measurements}, volume={232}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2020.106032}, abstractNote={Intensive agricultural activities, especially in artificially drained agricultural landscapes, generate a considerable amount of nutrient export, which has been identified as a primary cause of water quality impairment. Several management practices have been developed and installed in agricultural watersheds to reduce nutrient export, e.g. nitrate-nitrogen (NO3-N). Although published research reported considerable water quality benefits of these practices, there exist many unanswered questions regarding the inherent processes and mechanisms that control nitrate fate and transport from drained agricultural landscape. To advance our understanding of processes and mechanisms, we deployed two high-frequency sampling systems in a drained agricultural field to investigate the relationship between agricultural drainage and nitrate concentrations (C-Q relationship). Results indicated that the high-frequency measuring system was able to capture the rapidly changing C-Q relationships at the experimental site, e.g. hysteresis patterns. The 22 identified storm events exhibited anti-clockwise behavior with high variability of flushing/dilution effects. In addition, high drainage flows contributed far more nitrate loading compared with lower flows. For instance, the top 10 % of drainage flow exported more than 50 % of the nitrate lost via subsurface drainage during the monitoring period. Additionally, we observed that animal waste application was the most influential practice to change the C-Q relationship by increasing the size of soil nitrogen pools. The insights obtained from the high-frequency water quality measurements could help provide practical suggestions regarding the design and management of conservation practices, such as controlled drainage, bioreactors, and saturated buffers, to improve their nitrogen removal efficiencies. This subsequently leads to better nutrient management in drained agricultural lands.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Liu, Wenlong and Youssef, Mohamed A. and Birgand, Francois P. and Chescheir, George M. and Tian, Shiying and Maxwell, Bryan M.}, year={2020}, month={Apr} }
 @article{muwamba_amatya_chescheir_nettles_appelboom_tollner_ssegane_youssef_birgand_callahan_2020, title={Response of Drainage Water Quality to Fertilizer Applications on a Switchgrass Intercropped Coastal Pine Forest}, volume={12}, ISSN={["2073-4441"]}, DOI={10.3390/w12051265}, abstractNote={The objectives of this study were (1) to test the hypothesis that fertilizer applications do not increase nutrient fluxes on a switchgrass/pine forest (IC) when compared to a mature pine forest (MP) and (2) to evaluate post-fertilization (post-fert, 2014–2016) fluxes of nitrogen (N) and phosphorus (P) on IC and compare them to those observed during switchgrass growth prior to fertilization (pre-fert, 2012–2014) and site preparation for switchgrass establishment (site prep, 2009–2012). Nitrogen and P were applied to IC, a paired pure switchgrass site (SG), and MP, each about 25 ha in size, in June 2014, and again in June 2015 for the IC and SG sites only. Nitrogen and P concentrations were measured biweekly and rainfall and drainage outflow were measured continuously. During post-fert, the mean N concentrations and total loads were lower (p < 0.05) in IC than in SG and MP. The mean NO3-N concentration and loads in IC were lower during post-fert than during site prep. The post-fert phosphate concentrations in IC were lower than they were during pre-fert and site prep. Frequent N and P applications in IC did not significantly (α = 0.05) increase N and P fluxes, likely due to plant uptake and sorption on the acidic site.}, number={5}, journal={WATER}, author={Muwamba, Augustine and Amatya, Devendra M. and Chescheir, George M. and Nettles, Jamie E. and Appelboom, Timothy and Tollner, Ernest W. and Ssegane, Hebert and Youssef, Mohamed A. and Birgand, Francois and Callahan, Timothy}, year={2020}, month={May} }
 @article{muwamba_amatya_ssegane_chescheir_appelboom_nettles_tollner_youssef_walega_birgand_2020, title={Response of Nutrients and Sediment to Hydrologic Variables in Switchgrass Intercropped Pine Forest Ecosystems on Poorly Drained Soil}, volume={231}, ISSN={["1573-2932"]}, DOI={10.1007/s11270-020-04808-3}, number={9}, journal={WATER AIR AND SOIL POLLUTION}, author={Muwamba, Augustine and Amatya, Devendra M. and Ssegane, Herbert and Chescheir, George M. and Appelboom, Timothy and Nettles, Jamie E. and Tollner, Ernest W. and Youssef, Mohamed A. and Walega, Andrzej and Birgand, Francois}, year={2020}, month={Aug} }
 @article{negm_youssef_chescheir_skaggs_2019, title={DRAINMOD-based tools for quantifying reductions in annual drainage flow and nitrate losses resulting from drainage water management on croplands in eastern North Carolina (vol 166, pg 86, 2016)}, volume={226}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.105811}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, L. M. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W.}, year={2019}, month={Dec} }
 @article{maxwell_birgand_schipper_christianson_tian_helmers_williams_chescheir_youssef_2019, title={Drying–Rewetting Cycles Affect Nitrate Removal Rates in Woodchip Bioreactors}, volume={48}, ISSN={0047-2425}, url={http://dx.doi.org/10.2134/jeq2018.05.0199}, DOI={10.2134/jeq2018.05.0199}, abstractNote={Woodchip bioreactors are widely used to control nitrogen export from agriculture using denitrification. There is abundant evidence that drying–rewetting (DRW) cycles can promote enhanced metabolic rates in soils. A 287‐d experiment investigated the effects of weekly DRW cycles on nitrate (NO3) removal in woodchip columns in the laboratory receiving constant flow of nitrated water. Columns were exposed to continuous saturation (SAT) or to weekly, 8‐h drying‐rewetting (8 h of aerobiosis followed by saturation) cycles (DRW). Nitrate concentrations were measured at the column outlets every 2 h using novel multiplexed sampling methods coupled to spectrophotometric analysis. Drying–rewetting columns showed greater export of total and dissolved organic carbon and increased NO3 removal rates. Nitrate removal rates in DRW columns increased by up to 80%, relative to SAT columns, although DRW removal rates decreased quickly within 3 d after rewetting. Increased NO3 removal in DRW columns continued even after 39 DRW cycles, with ∼33% higher total NO3 mass removed over each weekly DRW cycle. Data collected in this experiment provide strong evidence that DRW cycles can dramatically improve NO3 removal in woodchip bioreactors, with carbon availability being a likely driver of improved efficiency. These results have implications for hydraulic management of woodchip bioreactors and other denitrification practices.}, number={1}, journal={Journal of Environment Quality}, publisher={American Society of Agronomy}, author={Maxwell, Bryan M. and Birgand, François and Schipper, Louis A. and Christianson, Laura E. and Tian, Shiying and Helmers, Matthew J. and Williams, David J. and Chescheir, George M. and Youssef, Mohamed A.}, year={2019}, pages={93} }
 @article{liu_youssef_chescheir_appelboom_poole_arellano_skaggs_2019, title={Effect of controlled drainage on nitrogen fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent}, volume={217}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.02.018}, abstractNote={Application of livestock manure has become a principal nutrient source in groundwater and surface water. The goal of this research was to investigate the effect of controlled drainage (CD) on nitrogen (N) fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent (SLE). A four-year field experiment was conducted on a naturally poorly drained pasture in eastern North Carolina. The 1.25 ha experimental field was artificially drained by subsurface drains installed at 1.0 m depth and 12.5 m spacing. Two treatments, replicated twice were implemented: conventional drainage (FD) and CD. The CD management protocol was more intensive compared to previous studies. The drain outlets of CD plot were set at 36 cm below soil surface all year round except several days before irrigation application when water table depth was shallower than 65 cm below surface. Controlled drainage significantly reduced drainage flow and TN loading via subsurface drain lines by an average of 397 mm yr−1 (93%) and 34.5 kg N ha−1 yr−1 (94%), respectively. DRAINMOD hydrologic simulations indicated that 96% of the reduction in predicted drain flow was attributed to increased lateral seepage. The nitrogen that did not drain from the field in response to CD was lost via enhanced denitrification (67%) and lateral seepage to adjacent fields (33%). This study clearly demonstrated how CD management affects the N fate and transport through seepage and denitrification process.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Liu, Yu and Youssef, Mohamed A. and Chescheir, George M. and Appelboom, Timothy W. and Poole, Chad A. and Arellano, Consuelo and Skaggs, R. Wayne}, year={2019}, month={May}, pages={440–451} }
 @article{cacho_youssef_shi_chescheir_skaggs_tian_leggett_sucre_nettles_arellano_2019, title={Impacts on soil nitrogen availability of converting managed pine plantation into switchgrass monoculture for bioenergy}, volume={654}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2018.11.133}, abstractNote={Biofuels derived from lignocellulosic materials is one of the options in addressing issues on climate change and energy independence. One of the most promising bioenergy crops is switchgrass (Panicum virgatum L.), particularly in North America. Future advancement in large-scale conversion of lignocellulosic feedstocks and relatively more competitive price for biomass and other economic advantages could lead to landowners opting to venture on switchgrass monoculture (SWITCH) in lieu of loblolly pine monoculture (PINE). Therefore, we investigated the conversion of previously managed loblolly pine stand into SWITCH in eastern North Carolina, U.S.A. on soil N availability. Treatments included PINE, SWTICH, and mature loblolly pine stand (REF). Each treatment was replicated three times on 0.8 ha plots drained by open ditches dug 1.0–1.2 m deep and spaced at 100 m. Rates of net N mineralization (Nm) and nitrification (Nn) at the top 20 cm were measured using sequential in-situ techniques in 2011 and 2012 (the 3rd and 4th years of establishment, respectively) along with a one-time laboratory incubation. On average, PINE, SWITCH, and REF can have field net Nm rates up to 0.40, 0.34 and 0.44 mg N·kg soil−1·d−1, respectively, and net Nn rates up to 0.14, 0.08 and 0.10 mg N·kg soil−1·d−1, respectively. Annually, net Nm rates ranged from 136.98 to 167.21, 62.00 to 142.61, and 63.57 to 127.95 kg N·ha−1, and net Nn rates were 56.31–62.98, 16.45–30.45, 31.99–32.94 kg N·ha−1 in PINE, SWITCH, and REF, respectively. Treatment effect was not significant on field Nm rate (p = 0.091). However, SWITCH significantly reduced nitrate-N production (p < 0.01). Overall, results indicated that establishment of SWITCH on poorly drained lands previously under PINE is less likely to significantly impact total soil N availability and potentially has minimum N leaching losses since soil mineral N under this system will be dominated by ammonium-N.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Cacho, Julian F. and Youssef, Mohamed A. and Shi, Wei and Chescheir, George M. and Skaggs, R. Wayne and Tian, Shiying and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2019}, month={Mar}, pages={1326–1336} }
 @article{maxwell_birgand_schipper_christianson_tian_helmers_williams_chescheir_youssef_2019, title={Increased Duration of Drying–Rewetting Cycles Increases Nitrate Removal in Woodchip Bioreactors}, volume={4}, ISSN={2471-9625}, url={http://dx.doi.org/10.2134/ael2019.07.0028}, DOI={10.2134/ael2019.07.0028}, abstractNote={Core Ideas
Nitrate removal in woodchips increased linearly with drying–rewetting duration.
Nitrate removal increased up to 172% in the longest drying–rewetting duration.
Nitrate removal rates increased proportionally with dissolved organic C leaching.
}, number={1}, journal={Agricultural & Environmental Letters}, publisher={American Society of Agronomy}, author={Maxwell, Bryan M. and Birgand, François and Schipper, Louis A. and Christianson, Laura E. and Tian, Shiying and Helmers, Matthew J. and Williams, David J. and Chescheir, George M. and Youssef, Mohamed A.}, year={2019} }
 @article{youssef_abdelbaki_negm_skaggs_thorp_jaynes_2018, title={DRAINMOD-simulated performance of controlled drainage across the US Midwest}, volume={197}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2017.11.012}, abstractNote={Controlled drainage (CD) has recently been proposed as a best management practice for reducing nutrient export from drained cropland in the U.S. Midwest to the Mississippi River and the Gulf of Mexico. We conducted a 25-year simulation study using the hydrological model, DRAINMOD, and the carbon and nitrogen (N) model, DRAINMOD-NII, to evaluate the performance of CD at 48 locations across the U.S. Midwest. Hydrological and Nitrogen predictions of this simulation study were compared to RZWQM-DSSAT predictions by Thorp et al. (2008). Simulation results showed that CD reduced annual subsurface drainage by 86 mm (30%) and annual N drainage losses by 10.9 kg N ha−1 (32%), on average over the 48 sites. DRAINMOD predicted highest reductions in drain flow at the south and southeast locations and lowest reductions at the northwest locations. The large reductions in drain flow in the south and southeast locations resulted in a large increase in surface runoff, which could increase soil erosion and sediment transport to surface water. In the north and northwest locations, the smaller amount of water that did not pass through the drainage system because of CD was primarily lost as evapotranspiration. DRAINMOD-NII predictions of annual reductions in N drainage loss followed the same trend of annual reductions in drainage flow. DRAINMOD-NII predictions show that reductions in N drainage loss under CD were mainly attributed to increase in denitrification. The declining trend in predicted annual denitrification from the southern to the northern locations of the Midwest region is most likely attributed to the lower temperature and less precipitation at the northern locations. RZWQM-DSSAT predicted reductions in annual drainage and N loss under CD conditions showed a similar trend to DRAINMOD/DRAINMOD-NII predictions. RZWQM-DSSAT, however, predicted substantially higher reductions in both drain flow (regional average of 151 mm yr−1, 53%) and N drainage losses (regional average of 18.9 kg N ha−1 yr−1, 51%). The discrepancies between DRAINMOD/DRAINMOD-NII and RZWQM-DSSAT predictions of annual reductions in drain flow and N loss under CD conditions were caused by differences in model predictions of individual components of the water and nitrogen balances under both free drainage and controlled drainage scenarios. Overall, this simulation study showed that climate variation across the region has a substantial impact on CD efficacy for reducing N drainage loss.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Youssef, Mohamed A. and Abdelbaki, Ahmed M. and Negm, Lamyaa M. and Skaggs, R. Wayne and Thorp, Kelly R. and Jaynes, Dan B.}, year={2018}, month={Jan}, pages={54–66} }
 @article{poole_skaggs_youssef_chescheir_crozier_2018, title={EFFECT OF DRAINAGE WATER MANAGEMENT ON NITRATE NITROGEN LOSS TO TILE DRAINS IN NORTH CAROLINA}, volume={61}, ISSN={["2151-0040"]}, DOI={10.13031/trans.12296}, abstractNote={Abstract.}, number={1}, journal={TRANSACTIONS OF THE ASABE}, author={Poole, C. A. and Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M. and Crozier, C. R.}, year={2018}, pages={233–244} }
 @article{cacho_youssef_chescheir_wayne skaggs_appelboom_leggett_sucre_nettles_arellano_2018, title={Effects of forest-based bioenergy feedstock production on shallow groundwater quality of a drained forest soil}, volume={631-632}, ISSN={0048-9697}, url={http://dx.doi.org/10.1016/J.SCITOTENV.2018.03.020}, DOI={10.1016/J.SCITOTENV.2018.03.020}, abstractNote={Managed forests in southern U.S. are a potential source of lignocellulosic biomass for biofuel production. Changes in management practices to optimize biomass production may impact the quality of waters draining to nutrient-sensitive waters in coastal plain regions. We investigated shallow groundwater quality effects of intercropping switchgrass (Panicum virgatum L.) with managed loblolly pine (Pinus taeda L.) to produce bioenergy feedstock and quality sawtimber in a poorly drained soil of eastern North Carolina, U.S.A. Treatments included PINE (traditional pine production), PSWITCH (pine-switchgrass intercropped), SWITCH (switchgrass monoculture) and REF (mature loblolly pine stand). Each treatment was replicated three times on 0.8 ha plots drained by parallel-open ditches, 1.0–1.2 m deep and 100 m apart. Water samples were collected monthly or more frequently after fertilizer application. Water samples were analyzed for organic nitrogen (ON), ammonium N (NH4+- N), and nitrite+nitrate N (NO3−+ NO2−- N), ortohophosphate phosphorus (OP), and total organic carbon (TOC). Overall, PSWITCH did not significantly affect shallow groundwater quality relative to PINE and SWITCH. ON, NO3−+ NO2−- N, and TOC concentrations in PSWITCH, PINE and SWITCH were substantially elevated during the two years after tree harvest and site establishment. The elevated nutrient concentrations at the beginning of the study were likely caused by a combination of rapid organic matter decomposition of the abundant supply of post-harvest residues, warming of exposed soil surfaces and reduction of plant nutrient uptake that can occur after harvesting, and pre-plant fertilization. Nutrient concentrations returned to background levels observed in REF during the third year after harvest.}, journal={Science of The Total Environment}, publisher={Elsevier BV}, author={Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Wayne Skaggs, R. and Appelboom, Timothy W. and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2018}, month={Aug}, pages={13–22} }
 @article{cacho_youssef_shi_chescheir_skaggs_tian_leggett_sucre_nettles_arellano_2018, title={Impacts of forest-based bioenergy feedstock production on soil nitrogen cycling}, volume={419-420}, ISSN={0378-1127}, url={http://dx.doi.org/10.1016/J.FORECO.2018.04.002}, DOI={10.1016/J.FORECO.2018.04.002}, abstractNote={We investigated impacts of simultaneous production of biomass for biofuel and quality timber on soil nitrogen (N) cycling in a poorly drained forest soil of eastern North Carolina, U.S.A. Treatments included traditional loblolly pine (PINE) and pine-switchgrass intercropping (PSWITCH). Treatments were replicated three times on 0.8 ha plots drained by parallel open ditches which were 1.2 m deep and spaced 100 m apart. Net N mineralization (Nm) and nitrification (Nn) rates were measured in the field using sequential in-situ technique over two years with multiple measurements in each year and laboratory by incubating soil samples for one-, two-, eight-, and thirteen weeks. Soil incubation in-situ or sample collection for laboratory incubation was conducted at nine sampling points within a 30 × 40 m subplot at each plot center and 20 cm from the soil surface. Soil samples were composited by location including near tree (NT), between two trees on the same bed (BT), and in the middle of four trees on two adjacent beds (M4T). Composite samples from NT and BT were categorized as tree-bed (BED), while those from M4T were grouped as interbed (INT). Field results showed that total soil N availability and its temporal variations over two years were not significantly affected by PSWITCH. However, it significantly reduced Nn rates, particularly in the INT. The plot-level mean Nm rates in PINE were 0.21 and 0.26 mg N·kg soil−1 d−1, while in PSWITCH they were 0.10 and 0.21 mg N kg soil−1 d−1 in 2011 and 2012, respectively. The plot-level mean Nn rates in PINE were 0.09 and 0.10 mg N kg soil−1 d−1 in 2011 and 2012, respectively, while in PSWITCH they remained at 0.03 mg N kg soil−1 d−1 across these two years. At the INT, mean Nn rates in PINE were 0.11 and 0.12 mg N kg soil−1 d−1 in 2011 and 2012, respectively, while in PSWITCH, Nn rate remained at 0.02 mg N kg soil−1 d−1 over two years. Laboratory results indicated that change in litter quality inputs (changing from mixed species to switchgrass) in the INT did not significantly affect Nm rates. Results of this study contributed to a better understanding of the changes in soil N cycling due to loblolly pine-switchgrass interactions, which is important in sustainable nutrient management of this new land use. Further, the results suggested that growing switchgrass as intercrop to managed loblolly pine has positive water quality implication since ammonium N is less mobile in soil than nitrate N.}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Cacho, Julian F. and Youssef, Mohamed A. and Shi, Wei and Chescheir, George M. and Skaggs, R. Wayne and Tian, Shiying and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2018}, month={Jul}, pages={227–239} }
 @article{tian_fischer_chescheir_youssef_cacho_king_2018, title={Microtopography-induced transient waterlogging affects switchgrass (Alamo) growth in the lower coastal plain of North Carolina, USA}, volume={10}, ISSN={["1757-1707"]}, DOI={10.1111/gcbb.12510}, abstractNote={Abstract}, number={8}, journal={GLOBAL CHANGE BIOLOGY BIOENERGY}, author={Tian, Shiying and Fischer, Milan and Chescheir, George M. and Youssef, Mohamed A. and Cacho, Julian F. and King, John S.}, year={2018}, month={Aug}, pages={577–591} }
 @article{ssegane_amatya_muwamba_chescheir_appelboom_tollner_nettles_youssef_birgand_skaggs_et al._2017, title={Calibration of paired watersheds: Utility of moving sums in presence of externalities}, volume={31}, ISSN={0885-6087}, url={http://dx.doi.org/10.1002/hyp.11248}, DOI={10.1002/hyp.11248}, abstractNote={Abstract}, number={20}, journal={Hydrological Processes}, publisher={Wiley}, author={Ssegane, H. and Amatya, D. M. and Muwamba, A. and Chescheir, G. M. and Appelboom, T. and Tollner, E. W. and Nettles, J. E. and Youssef, M. A. and Birgand, François and Skaggs, R. W. and et al.}, year={2017}, month={Sep}, pages={3458–3471} }
 @article{negm_youssef_jaynes_2017, title={Evaluation of DRAINMOD-DSSAT simulated effects of controlled drainage on crop yield, water balance, and water quality for a corn-soybean cropping system in central Iowa}, volume={187}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2017.03.010}, abstractNote={Controlled drainage (CD) has been identified as a sustainable management practice whereby more soil water can be conserved and less nutrients are leached; alongside its potential benefit of alleviating drought stress and increasing yield. More than 12 million hectare of cropland in the US Midwest are suitable for implementing CD; however, the effectiveness of the practice can vary across the region with the variation in environmental conditions and management practices. The main objective of this study is to evaluate the performance of the integrated agro-ecosystem model; DRAINMOD-DSSAT, for simulating the effects of CD on drainage flow, nitrogen losses via drainage water and crop yield. Herein, we utilized a 4-yr dataset (2006–2009) that was collected from a corn–soybean cropping system near Story City, Iowa. This site was artificially drained under free drainage (FD) and CD treatments. The model was calibrated using the data collected from the FD plots, and validated for the CD plots. DRAINMOD-DSSAT predictions of drainage flow and nitrate-nitrogen (NO3-N) losses were in good agreement with measured values under FD and CD, with the former treatment showed slightly better performance. The modeling efficiencies (NSE’s) for simulating monthly drainage flows were 0.81 and 0.60 for FD and CD, respectively. Monthly NO3–N mass losses were simulated with NSE’s of 0.76 and 0.66 for FD and CD, respectively. DRAINMOD-DSSAT well simulated CD-induced percent reductions in annual drainage flow (measured = 24.6%, simulated = 27.1%), and NO3-N losses (measured = 34.8%, simulated = 33.5%). Low percent error (PE) values were associated with the model predictions of corn yields (−1.3 ≤ PE ≤ 1.3) and soybean yields (−6.0 ≤ PE ≤ 12.6). Overall, results obtained from this relatively short-term modeling study demonstrated the potential use of DRAINMOD-DSSAT as a management design tool. Yet, further model testing CD effectiveness under different conditions is critically needed to establish a higher credibility in model predictions and to allow for further model improvement and expansion.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, Lamyaa M. and Youssef, Mohamed A. and Jaynes, Dan B.}, year={2017}, month={Jun}, pages={57–68} }
 @article{golmohammadi_rudra_prasher_madani_youssef_goel_mohammadi_2017, title={Impact of tile drainage on water budget and spatial distribution of sediment generating areas in an agricultural watershed}, volume={184}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2017.02.001}, abstractNote={A recently developed model, SWATDRAIN, was used to assess the alterations in water balance components, discharge, and sediment loads due to tile drainage practices in a heavily tile drained watershed in Ontario, Canada. Furthermore, the model was implemented to determine the spatial variability of sediment loads which can be explained by a combination of spatially distributed variables within a watershed, including those controlling the hydrology, geology, soil and land use. Three scenarios were examined across the watershed, including conventional drainage (existing condition), controlled drainage, and no tile drainage. The model predicted that streamflow was not significantly impacted due to tile drainage, while the total runoff and sediment loads from the basin due to controlled drainage were increased by 27.1% and 22.2%, respectively, while removing tile drain infrastructures resulted in 37.1% increase in surface runoff and 55% increase in sediment load from the watershed The areas with high sediment load generation were identified by the model and the impact of tile drainage in producing sediment in those areas was assessed. The results showed that the sediment load generation rate in the areas with the highest load (class V) increased by 8% only due to controlled drainage, while in the second ranked sediment generating areas (class IV), the sediment load generation rate was increased by 32%.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Golmohammadi, Golmar and Rudra, Ramesh and Prasher, Shiv and Madani, Ali and Youssef, Mohamed and Goel, Pradeep and Mohammadi, Kourosh}, year={2017}, month={Apr}, pages={124–134} }
 @article{tian_cacho_youssef_chescheir_fischer_nettles_king_2017, title={Switchgrass growth and pine-switchgrass interactions in established intercropping systems}, volume={9}, ISSN={["1757-1707"]}, DOI={10.1111/gcbb.12381}, abstractNote={Abstract}, number={5}, journal={GLOBAL CHANGE BIOLOGY BIOENERGY}, author={Tian, Shiying and Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Fischer, Milan and Nettles, Jami E. and King, John S.}, year={2017}, month={May}, pages={845–857} }
 @article{tilak_youssef_burchell_lowrance_williams_2017, title={Testing the riparian ecosystem management model (REMM) on a riparian buffer with dilution from deep groundwater}, volume={60}, number={2}, journal={Transactions of the ASABE}, author={Tilak, A. S. and Youssef, M. A. and Burchell, M. R. and Lowrance, R. R. and Williams, R. G.}, year={2017}, pages={377–392} }
 @article{muwamba_amatya_chescheir_nettles_appelboom_ssegane_tollner_youssef_birgand_skaggs_et al._2017, title={Water Quality Effects of Switchgrass Intercropping on Pine Forest in Coastal North Carolina}, volume={60}, ISSN={2151-0040}, url={http://dx.doi.org/10.13031/trans.12181}, DOI={10.13031/trans.12181}, abstractNote={Abstract.}, number={5}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Muwamba, Augustine and Amatya, Devendra M. and Chescheir, George M. and Nettles, Jami E. and Appelboom, Timothy and Ssegane, Herbert and Tollner, Ernest E and Youssef, Mohamed A. and Birgand, Francois and Skaggs, R. Wayne and et al.}, year={2017}, pages={1607–1620} }
 @article{negm_youssef_chescheir_skaggs_2016, title={DRAINMOD-based tools for quantifying reductions in annual drainage flow and nitrate losses resulting from drainage water management on croplands in eastern North Carolina}, volume={166}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2015.12.014}, abstractNote={Nitrogen (N) leachate of drained agriculture has continued to be pervasive in the U.S. water resources. Nitrogen credit exchange program is a trading market to facilitate pollutant reductions and protect the environment. A simple tool suitable for eastern North Carolina (NC) was developed to quantify drainage flow and N mass reductions resulting from drainage water management (DWM); an efficient and common conservation practice for drained agricultural lands. The tool comprises a set of regression equations estimating the performance of DWM as a function of local site conditions. DRAINMOD and DRAINMOD-NII models simulations were conducted for a wide range of soil types, weather conditions, and management practices for different locations in eastern NC. Simulation results were used with SAS 9.3 software to develop a set of multi-linear regression equations to estimate DWM-caused reductions in annual drainage flow and corresponding nitrate-N (NO3-N) losses for continuous corn (CC) and corn–wheat–soybean (CWS) cropping systems. The regression model estimations of annual drainage flow were highly correlated with DRAINMOD simulated values with an adjusted coefficient of multiple determination (R2adj) equal to 0.91 or higher for different management scenarios. Similarly, the regression model estimations of annual nitrate losses achieved an R2adj of 0.88 or higher for all management scenarios. The developed regression models were further compared on a year-by-year basis to the calibrated DRAINMOD and DRAINMOD-NII models for local conditions of an experimental site in eastern NC over 25 years. Estimated annual drainage flow and NO3-N losses were in good agreement with corresponding values simulated by DRAINMOD-based models for CC and CWS under free and controlled drainage modes. In terms of DWM-induced annual reductions in drainage flow and N losses, noticeable differences occurred in several years between predictions of DRAINMOD-NII and the regression models. A comparison based on the 5-year moving average of DWM-induced reductions smoothed out the extreme year-to-year variations and indicated very similar reduction trends provided by both methods. The results presented in this case study indicated that the simple regression method provides an adequate alternative to the processes based DRAINMOD suite of models for estimating annual reductions in drainage rates and N mass losses resulting from implementation of DWM. Similar tools can be developed for other regions in the US and abroad that initiate nitrogen trading markets involving DWM.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, L. M. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W.}, year={2016}, month={Mar}, pages={86–100} }
 @article{tian_youssef_chescheir_skaggs_cacho_nettles_2016, title={Development and preliminary evaluation of an integrated field scale model for perennial bioenergy grass ecosystems in lowland areas}, volume={84}, ISSN={1364-8152}, url={http://dx.doi.org/10.1016/J.ENVSOFT.2016.06.029}, DOI={10.1016/J.ENVSOFT.2016.06.029}, abstractNote={Computer models are useful tools for evaluating environmental and economic sustainability of proposed dedicated cellulosic grass ecosystems for biofuel production. This study developed an integrated, field scale, and process-based ecosystem model (DRAINMOD-GRASS) for simulating hydrological processes, soil carbon and nitrogen cycling, and plant growth in cropping systems for producing bioenergy grasses in lowland areas. We tested the model using measurements from three replicated switchgrass (Panicum virgatum) plots located in eastern North Carolina, USA. Results showed that the model accurately predicted 5-year (2009–2013) biomass yield. Predicted daily water table depth closely matched field measurements with Nash-Sutcliffe coefficient of 0.86. The model also accurately predicted temporal dynamics of daily soil moisture and temperature with Nash-Sutcliffe coefficients of 0.7 and 0.9, respectively. Predicted seasonal changes in net N mineralization and nitrification rates were comparable to field measurements in 2011 and 2012.}, journal={Environmental Modelling & Software}, publisher={Elsevier BV}, author={Tian, S. and Youssef, M.A. and Chescheir, G.M. and Skaggs, R.W. and Cacho, J. and Nettles, J.}, year={2016}, month={Oct}, pages={226–239} }
 @article{tian_youssef_richards_liu_baker_liu_2016, title={Different seasonality of nitrate export from an agricultural watershed and an urbanized watershed in Midwestern USA}, volume={541}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2016.08.042}, abstractNote={Land use/land cover is a critical factor affecting temporal dynamics of nitrate export from watersheds. Based on a long-term (>30 years) water quality monitoring program in the Western Lake Erie area, United States, this study compared seasonal variation of nitrate export from an agricultural watershed and an urbanized watershed. A seasonality index was adapted to quantitatively characterize seasonal variation of nitrate export from the two watersheds. Results showed that monthly nitrate concentrations from the two watersheds exhibited different seasonal variation. Seasonality index of monthly nitrate loading for the agricultural watershed is approximately 3 times of that from the urbanized watershed and the difference is statistically significant (p < 0.0001). Meanwhile, calculated historical seasonality indexes of monthly nitrate loading for both watersheds exhibited significant (p < 0.05) decreasing trends according to the non-seasonal Mann-Kendall test. The identified differences in seasonal nitrate export from the two watersheds were mainly attributed to their distinct nitrogen sources, physical and biogeochemical settings. The declining seasonality index of monthly nitrate loading from the agricultural watershed could be partially caused by historical climate change in the study region, especially increased temperature during winter. Urbanization could be one key factor contributing to the declining seasonality index of monthly nitrate loading from the urbanized watershed. Information derived from this study have practical implications for developing proper management practices to mitigate nitrate pollution in Midwestern United States.}, journal={JOURNAL OF HYDROLOGY}, author={Tian, S. and Youssef, M. A. and Richards, R. P. and Liu, J. and Baker, D. B. and Liu, Y.}, year={2016}, month={Oct}, pages={1375–1384} }
 @article{skaggs_tian_chescheir_amatya_youssef_2016, title={Forest drainage}, DOI={10.1079/9781780646602.0124}, abstractNote={This chapter reviews the impacts of drainage on forest production and the hydrology of forested lands. It is established that drainage is used to improve access and yields on a small percentage of the world's forested lands. However, it has had a big impact on the millions of hectares on which it is applied. Drainage has increased timber yields on poorly drained peatlands and mineral soils in northern Europe, Canada and the southern USA.}, journal={Forest Hydrology: Processes, Management and Assessment}, author={Skaggs, R. W. and Tian, S. and Chescheir, G. M. and Amatya, D. M. and Youssef, M. A.}, year={2016}, pages={124–140} }
 @article{daggupati_pai_ale_douglas-mankin_zeckoski_jeong_parajuli_saraswat_youssef_2015, title={A recommended calibration and validation strategy for hydrologic and water quality models}, volume={58}, number={6}, journal={Transactions of the ASABE}, author={Daggupati, P. and Pai, N. and Ale, S. and Douglas-Mankin, K. R. and Zeckoski, R. W. and Jeong, J. and Parajuli, P. B. and Saraswat, D. and Youssef, M. A.}, year={2015}, pages={1705–1719} }
 @article{radcliffe_reid_blomback_bolster_collick_easton_francesconi_fuka_johnsson_king_et al._2015, title={Applicability of models to predict phosphorus losses in drained fields: A review}, volume={44}, number={2}, journal={Journal of Environmental Quality}, author={Radcliffe, D. E. and Reid, D. K. and Blomback, K. and Bolster, C. H. and Collick, A. S. and Easton, Z. M. and Francesconi, W. and Fuka, D. R. and Johnsson, H. and King, K. and et al.}, year={2015}, pages={614–628} }
 @article{muwamba_amatya_ssegane_chescheir_appelboom_tollner_nettles_youssef_birgand_skaggs_et al._2015, title={Effects of Site Preparation for Pine Forest/Switchgrass Intercropping on Water Quality}, volume={44}, ISSN={0047-2425}, url={http://dx.doi.org/10.2134/jeq2014.11.0505}, DOI={10.2134/jeq2014.11.0505}, abstractNote={A study was initiated to investigate the sustainability effects of intercropping switchgrass ( L.) in a loblolly pine ( L.) plantation. This forest-based biofuel system could possibly provide biomass from the perennial energy grass while maintaining the economics and environmental benefits of a forest managed for sawtimber. Operations necessary for successful switchgrass establishment and growth, such as site preparation, planting, fertilizing, mowing and baling, may affect hydrology and nutrient runoff. The objectives of this study were (i) to characterize the temporal effects of management on nutrient concentrations and loadings and (ii) to use pretreatment data to predict those treatment effects. The study watersheds (∼25 ha each) in the North Carolina Atlantic Coastal Plain were a pine/switchgrass intercropped site (D1), a midrotation thinned pine site with natural understory (D2), and a switchgrass-only site (D3). Rainfall, drainage, water table elevation, nitrogen (total Kjedahl N, NH-N, and NO-N), and phosphate were monitored for the 2007-2008 pretreatment and the 2009-2012 treatment periods. From 2010 to 2011 in site D1, the average NO-N concentration effects decreased from 0.18 to -0.09 mg L, and loads effects decreased from 0.86 to 0.49 kg ha. During the same period in site D3, the average NO-N concentration effects increased from 0.03 to 0.09 mg L, and loads effects increased from -0.26 to 1.24 kg ha. This study shows the importance of considering water quality effects associated with intensive management operations required for switchgrass establishment or other novel forest-based biofuel systems.}, number={4}, journal={Journal of Environment Quality}, publisher={American Society of Agronomy}, author={Muwamba, A. and Amatya, D. M. and Ssegane, H. and Chescheir, G.M. and Appelboom, T. and Tollner, E.W. and Nettles, J. E. and Youssef, M. A. and Birgand, F. and Skaggs, R. W. and et al.}, year={2015}, pages={1263} }
 @article{baffaut_dabney_smolen_youssef_bonta_chu_guzman_shedekar_jha_arnold_2015, title={Hydrologic and water quality modeling: Spatial and temporal considerations}, volume={58}, number={6}, journal={Transactions of the ASABE}, author={Baffaut, C. and Dabney, S. M. and Smolen, M. D. and Youssef, M. A. and Bonta, J. V. and Chu, M. L. and Guzman, J. A. and Shedekar, V. S. and Jha, M. K. and Arnold, J. G.}, year={2015}, pages={1661–1680} }
 @article{saraswat_frankenberg_pai_ale_daggupati_douglas-mankin_youssef_2015, title={Hydrologic and water quality models: Documentation and reporting procedures for calibration, validation, and use}, volume={58}, number={6}, journal={Transactions of the ASABE}, author={Saraswat, D. and Frankenberg, J. R. and Pai, N. and Ale, S. and Daggupati, P. and Douglas-Mankin, K. R. and Youssef, M. A.}, year={2015}, pages={1787–1797} }
 @article{arnold_youssef_yen_white_sheshukov_sadeghi_moriasi_steiner_amatya_skaggs_et al._2015, title={Hydrological processes and model representation: Impact of soft data on calibration}, volume={58}, DOI={10.13031/trans.58.10726}, abstractNote={Hydrologic and water quality models are increasingly used to determine the environmental impacts of climate variability and land management. Due to differing model objectives and differences in monitored data, there are currently no universally accepted procedures for model calibration and validation in the literature. In an effort to develop accepted model calibration and validation procedures or guidelines, a special collection of 22 research articles that present and discuss calibration strategies for 25 hydrologic and water quality models was previously assembled. The models vary in scale temporally as well as spatially from point source to the watershed level. One suggestion for future work was to synthesize relevant information from this special collection and to identify significant calibration and validation topics. The objective of this article is to discuss the importance of accurate representation of model processes and its impact on calibration and scenario analysis using the information from these 22 research articles and other relevant literature. Models are divided into three categories: (1) flow, heat, and solute transport, (2) field scale, and (3) watershed scale. Processes simulated by models in each category are reviewed and discussed. In this article, model case studies are used to illustrate situations in which a model can show excellent statistical agreement with measured stream gauge data, while misrepresented processes (water balance, nutrient balance, sediment source/sinks) within a field or watershed can cause errors when running management scenarios. These errors may be amplified at the watershed scale where additional sources and transport processes are simulated. To account for processes in calibration, a diagnostic approach is recommended using both hard and soft data. The diagnostic approach looks at signature patterns of behavior of model outputs to determine which processes, and thus parameters representing them, need further adjustment during calibration. This overcomes the weaknesses of traditional regression-based calibration by discriminating between multiple processes within a budget. Hard data are defined as long-term, measured time series, typically at a point within a watershed. Soft data are defined as information on individual processes within a budget that may not be directly measured within the study area, may be just an average annual estimate, and may entail considerable uncertainty. The advantage of developing soft data sets for calibration is that they require a basic understanding of processes (water, sediment, nutrient, and carbon budgets) within the spatial area being modeled and constrain the calibration.}, number={6}, journal={Transactions of the ASABE}, author={Arnold, J. G. and Youssef, M. A. and Yen, H. and White, M. J. and Sheshukov, A. Y. and Sadeghi, A. M. and Moriasi, D. N. and Steiner, J. L. and Amatya, D. M. and Skaggs, R. W. and et al.}, year={2015}, pages={1637–1660} }
 @article{cacho_youssef_chescheir_skaggs_leggett_sucre_nettles_arellano_2015, title={Impacts of switchgrass-loblolly pine intercropping on soil physical properties of a drained forest}, volume={58}, DOI={10.13031/trans.58.11238}, abstractNote={Intercropping switchgrass ( L.) with managed loblolly pine ( L.) has been proposed as an alternative source of bioenergy feedstock that does not require conversion of agricultural cropland. Different management practices may alter soil physical properties (SPP), which could influence productivity, hydrologic and biogeochemical processes. Therefore, we investigated the effect of switchgrass-loblolly pine intercropping on the SPP of a poorly drained forest soil in eastern North Carolina using three management regimes: young loblolly pine stand (PINE), switchgrass-pine intercropping (PSWITCH), and a 38-year-old loblolly pine stand (REF). Measurements of SPP were conducted before and after the third annual harvesting operation using intact soil cores taken from three points within each of three replicated plots and at three depths: 0-15 cm, 15-30 cm, and 30-45 cm. Pre- and post-harvest values of SPP in PSWITCH were not significantly different. Compared to PINE, changes in bulk density and in both total porosity and saturated hydraulic conductivity in PSWITCH were significant only in the top 30 and 15 cm of soil, respectively. Volume drained and drainable porosity in PSWITCH decreased significantly at water table depths ≤45 cm. Cumulative effects of V-shearing for switchgrass seedbed preparation and the first and second harvest operations may have caused structural changes to the surface soil layer in PSWITCH that subsequently resulted in the measured differences in SPP between PSWITCH and PINE. We suggest that soil disturbance should be minimized during field operations to lessen the adverse effects on SPP, and models used to quantify impacts of management practices and land use change on the hydrology and biogeochemistry of managed forests should consider SPP changes caused by management regimes.}, number={6}, journal={Transactions of the ASABE}, author={Cacho, J. F. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W. and Leggett, Zakiya H and Sucre, E. B. and Nettles, J. E. and Arellano, C.}, year={2015}, pages={1573–1583} }
 @article{tian_cacho_youssef_chescheir_nettles_2015, title={Switchgrass growth and morphological changes under established pine-grass agroforestry systems in the lower coastal plain of North Carolina, United States}, volume={83}, ISSN={["1873-2909"]}, DOI={10.1016/j.biombioe.2015.10.002}, abstractNote={Switchgrass (Panicum virgatum L.) intercropped with Loblolly pine (Pinus taeda L.) has been proposed as a potential biomass feedstock for biofuel production in the southeastern United States. This study investigated effects of treatments (intercropping vs. grass only) on biomass increment processes and morphological properties of switchgrass at two experimental plots (Lenoir1) located in the coastal plain of North Carolina. We also evaluated effects of trimming lower tree branches of pine trees on switchgrass growth at another watershed-scale site (Carteret7) in the same region. Results showed that biomass yield of intercropped switchgrass was reduced by adjacent trees and negatively affected by relative position of grass to trees at the 6th year after planting at Lenoir1. Relative grass-to-tree position was also found to be a significant (p < 0.001) factor affecting grass growth at Carteret7 site with tree age of 5 years old, which is irrespective to the trimming practice. Trimming lower tree branches did not significantly (p = 0.57) improve biomass yield of switchgrass at Carteret7. We also observed intercropped switchgrass typically had higher specific leaf area and grew taller compared to grass-only plots. Stem-to-leaf ratios of switchgrass were significantly (p = 0.02) affected by trees at Lenoir1, but not by trimming lower branches in Carteret7 and relative position of grass to trees at both study sites. Findings from this study are important for evaluating the viability of producing biofuel feedstocks using this proposed intercropping system in the southeastern United States.}, journal={BIOMASS & BIOENERGY}, author={Tian, Shiying and Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Nettles, Jami E.}, year={2015}, month={Dec}, pages={233–244} }
 @article{tian_youssef_sun_chescheir_noormets_amatya_skaggs_king_mcnulty_gavazzi_et al._2015, title={Testing DRAINMOD-FOREST for predicting evapotranspiration in a mid-rotation pine plantation}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.03.028}, abstractNote={Evapotranspiration (ET) is a key component of the hydrologic cycle in terrestrial ecosystems and accurate description of ET processes is essential for developing reliable ecohydrological models. This study investigated the accuracy of ET prediction by the DRAINMOD-FOREST after its calibration/validation for predicting commonly measured hydrological variables. The model was tested by conducting an eight year simulation of drainage and shallow groundwater dynamics in a managed mid-rotation loblolly pine (Pinus taeda L.) plantation located in the coastal plain of North Carolina, USA. Modeled daily ET rates were compared to those measured in the field using the eddy covariance technique. In addition, the wavelet transform and coherence analysis were used to compare ET predictions and measurements on the time–frequency domain. Results showed that DRAINMOD-FOREST accurately predicted annual and monthly ET after a successful calibration and validation using measured drainage rates and water table depth. The model under predicted ET on an annual basis by 2%, while the Nash–Sutcliffe coefficient of model predictions on a monthly basis was 0.78. Results from wavelet transform and coherence analysis demonstrated that the model reasonably captured the high power spectra of ET at an annual scale with significantly high model-data coherency. These results suggested that the calibrated DRAINMOD-FOREST collectively captured key factors and mechanisms controlling ET dynamics in the drained pine plantation. However, the global power spectrum revealed that the model over predicted the power spectrum of ET at an annual scale, suggesting the model may have under predicted canopy conductance during non-growing seasons. In addition, this study also suggested that DRAINMOD-FOREST did not properly capture the seasonal dynamics of ET under extreme drought conditions with deeper water table depths. These results suggested further refinement to parameters, particularly vegetation related, and structures of DRAINMOD-FOREST to achieve better agreement between ET predictions and measurements in the time–frequency domain.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Tian, Shiying and Youssef, Mohamed A. and Sun, Ge and Chescheir, George M. and Noormets, Asko and Amatya, Devendra M. and Skaggs, R. Wayne and King, John S. and McNulty, Steve and Gavazzi, Michael and et al.}, year={2015}, month={Nov}, pages={37–47} }
 @article{negm_youssef_skaggs_chescheir_kladivko_2014, title={DRAINMOD-DSSAT Simulation of the Hydrology, Nitrogen Dynamics, and Plant Growth of a Drained Corn Field in Indiana}, volume={140}, ISSN={["1943-4774"]}, DOI={10.1061/(asce)ir.1943-4774.0000738}, abstractNote={AbstractDRAINMOD-DSSAT is an integrated model recently developed to simulate the hydrology, water quality, and crop growth for artificially drained croplands. DRAINMOD-DSSAT is an advanced research tool that contributes to increasing productivity, reducing cost, and enhancing sustainability of crop production on high water table soils with artificial drainage. In this study, the performance of the model was evaluated using a six-year data set (1985–1990) collected from a subsurface drained agricultural research site in Indiana in the United States. Subsurface drains were installed at three different spacings (5, 10, and 20 m). During the simulation period, all treatments were planted to corn receiving high preplant N-fertilization rates. Rainfall patterns varied significantly among the years. DRAINMOD-DSSAT predictions of monthly and annual drainage flow, and nitrate losses, were in good agreement with measured values. Similarly, variations in corn yield patterns were well captured by the model across dif...}, number={8}, journal={JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING}, author={Negm, Lamyaa M. and Youssef, Mohamed A. and Skaggs, Richard W. and Chescheir, George M. and Kladivko, Eileen J.}, year={2014}, month={Aug} }
 @article{negm_youssef_skaggs_chescheir_jones_2014, title={DRAINMOD–DSSAT model for simulating hydrology, soil carbon and nitrogen dynamics, and crop growth for drained crop land}, volume={137}, ISSN={0378-3774}, url={http://dx.doi.org/10.1016/J.AGWAT.2014.02.001}, DOI={10.1016/J.AGWAT.2014.02.001}, abstractNote={Integrated agricultural systems modeling represents an effective research tool to meet the evolving challenges facing agricultural production and environmental quality. An integrated, process-based model was developed to simulate the impacts of the changing environment and different water and farming management practices on the hydrology, water quality, and crop growth and yield for artificially drained cropping systems. The new model; named DRAINMOD–DSSAT, was developed by integrating three different process based models: the hydrological model, DRAINMOD; the soil carbon and nitrogen (N) dynamics model; DRAINMOD-NII, and selected crop modules of the DSSAT–CSM model; CROPGRO and CERES-Maize. The integration of the three component models is implemented at the source code level and allows for daily interactions and feedback among simulated climatic conditions, soil water and nitrogen, and crop growth. DRAINMOD–DSSAT performance was evaluated using a 10-yr dataset collected from a corn–soybean production system on a subsurface drained field in Iowa, with corn receiving low, medium, and high N fertilization rates. The model was calibrated using the data collected from the high-N treatment, and validated for the other two treatments. Annual and monthly subsurface drainage outflows were predicted with modeling efficiencies (NSE) of 0.95 and 0.83, respectively. The NSE's for annual and monthly NO3–N mass losses were 0.87 and 0.70 for the high N-treatment, 0.93 and 0.86 for the medium N-treatment, 0.94 and 0.67 for the low N-treatment, respectively. Predicted and measured crop yields were accurately predicted with an absolute percent error less than 8% in 27 of the 30 simulated plot-years (3 plots × 10 yrs). Nitrogen removal in crop grain was reasonably predicted. This first model application suggested the potential capability of DRAINMOD–DSSAT of simulating the hydrology, water quality, and crop growth and yield for corn and soybean production on artificially drained fields in response to varying climatic conditions and nutrient management practices. Further research, using more intense field measurements, is needed to validate the model for its intended use.}, journal={Agricultural Water Management}, publisher={Elsevier BV}, author={Negm, L.M. and Youssef, M.A. and Skaggs, R.W. and Chescheir, G.M. and Jones, J.}, year={2014}, month={May}, pages={30–45} }
 @article{tilak_burchell_youssef_lowrance_williams_2014, title={FIELD TESTING THE RIPARIAN ECOSYSTEM MANAGEMENT MODEL ON A RIPARIAN BUFFER IN THE NORTH CAROLINA UPPER COASTAL PLAIN}, volume={50}, ISSN={["1752-1688"]}, DOI={10.1111/jawr.12208}, abstractNote={Abstract}, number={3}, journal={JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION}, author={Tilak, Amey S. and Burchell, Michael R., II and Youssef, Mohamed A. and Lowrance, Richard R. and Williams, Randy G.}, year={2014}, month={Jun}, pages={665–682} }
 @article{tian_youssef_amatya_vance_2014, title={Global sensitivity analysis of DRAINMOD-FOREST, an integrated forest ecosystem model}, volume={28}, ISSN={["1099-1085"]}, DOI={10.1002/hyp.9948}, abstractNote={Global sensitivity analysis is a useful tool to understand process‐based ecosystem models by identifying key parameters and processes controlling model predictions. This study reported a comprehensive global sensitivity analysis for DRAINMOD‐FOREST, an integrated model for simulating water, carbon (C), and nitrogen (N) cycles and plant growth in lowland forests. The analysis was carried out for multiple long‐term model predictions of hydrology, biogeochemistry, and plant growth. Results showed that long‐term mean hydrological predictions were highly sensitive to several key plant physiological parameters. Long‐term mean annual soil organic C content and mineralization rate were mainly controlled by temperature‐related parameters for soil organic matter decomposition. Mean annual forest productivity and N uptake were found to be mainly dependent upon plant production‐related parameters, including canopy quantum use efficiency and carbon use efficiency. Mean annual nitrate loss was highly sensitive to parameters controlling both hydrology and plant production, while mean annual dissolved organic nitrogen loss was controlled by parameters associated with its production and physical sorption. Parameters controlling forest production, C allocation, and specific leaf area highly affected long‐term mean annual leaf area. Results of this study could help minimize the efforts needed for calibrating DRAINMOD‐FOREST. Meanwhile, this study demonstrates the critical role of plants in regulating water, C, and N cycles in forest ecosystems and highlights the necessity of incorporating a dynamic plant growth model for comprehensively simulating hydrological and biogeochemical processes. Copyright © 2013 John Wiley & Sons, Ltd.}, number={15}, journal={HYDROLOGICAL PROCESSES}, author={Tian, Shiying and Youssef, Mohamed A. and Amatya, Devendra M. and Vance, Eric D.}, year={2014}, month={Jul}, pages={4389–4410} }
 @article{salazar_wesstrom_joel_youssef_2013, title={Application of an integrated framework for estimating nitrate loads from a coastal watershed in south-east Sweden}, volume={129}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2013.07.020}, abstractNote={Nitrate-nitrogen (NO3-N) loading from a 734 ha coastal watershed draining into the Baltic Sea off south-east Sweden was simulated using a simple modelling approach in which the nitrogen model DRAINMOD-N II and a temperature-dependent NO3-N removal equation were incorporated into the Arc Hydro-DRAINMOD framework. Hydrology and water quality data collected during six periods between 2003 and 2007 were used to test Arc Hydro-DRAINMOD and its performance was evaluated by considering uncertainty in model parameters using GLUE methodology. The GLUE estimates (5th and 95th percentiles) and calculated monthly NO3-N loads were in satisfactory agreement. There are some sources of errors that may affect the performance of the framework, such as NO3-N load calculations, soil denitrification and in-stream removal of NO3-N. Although additional measurements may help to improve the understanding of these processes and reduce uncertainty, they cannot completely eliminate the uncertainty in framework predictions. These uncertainties must be evaluated by some methodology, such as the GLUE procedure. Sensitivity analysis showed the framework to be most sensitive to changes in stream baseflow and N removal processes in the stream network. These results show that the Arc Hydro-DRAINMOD framework can be an effective tool to support water stakeholders in managing NO3-N loading from small tile-drained watersheds at monthly time step.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Salazar, Osvaldo and Wesstrom, Ingrid and Joel, Abraham and Youssef, Mohamed A.}, year={2013}, month={Nov}, pages={56–68} }
 @article{ale_gowda_mulla_moriasi_youssef_2013, title={Comparison of the performances of DRAINMOD-NII and ADAPT models in simulating nitrate losses from subsurface drainage systems}, volume={129}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2013.07.008}, abstractNote={Adequate knowledge on the movement of nitrate-nitrogen (NO3-N) under different subsurface (tile) drain configurations and management practices in the U.S. Midwest is essential for developing remedial measures for reducing hypoxic conditions in the Gulf of Mexico. In this study, DRAINMOD-NII, a daily time-step soil carbon (C) and N model, was calibrated and validated for subsurface drainage and associated NO3-N losses, and crop yield. Long term (1983–1996) monitoring data measured on three experimental plots under continuous corn (Zea mays L.) with conventional tillage practice at the University of Minnesota's Southern Research and Outreach Center near Waseca, southern Minnesota was used for this purpose. Nash-Sutcliffe efficiency (NSE), Percent Error (PE) and Index of agreement (d) were used for assessing the model performance. DRAINMOD-NII predicted monthly subsurface drainage matched well with measured data during calibration (NSE = 0.81, PE = −7.8% and d = 0.94) and validation (NSE = 0.67, PE = −0.7% and d = 0.88) periods. Performance of DRAINMOD-NII for predicting monthly NO3-N losses in subsurface drainage was also good for both calibration (NSE = 0.64, PE = 0.8%, and d = 0.85) and validation (NSE = 0.62, PE = −5.3%, and d = 0.83) periods. DRAINMOD-NII predicted average (1983–1992) annual corn relative yield (93%), a ratio of crop yield in a year to the long-term average crop yield, was close to the observed relative yield (92.5%). DRAINMOD-NII simulation results were also compared and contrasted with those obtained by the Agricultural Drainage and Pesticide Transport (ADAPT) model with the same dataset. Both models performed equally well in predicting monthly subsurface drainage. However, DRAINMOD-NII performed slightly better in predicting monthly NO3-N losses and annual N budget, in addition to showing potential to simulate the effects of excess and deficit water stresses on crop yield. Studies comparing performances of different drainage models in the U.S. Midwest are useful to select an appropriate model for devising various strategies for reducing NO3-N losses from subsurface drainage systems, and thereby minimizing hypoxic conditions in the Gulf of Mexico.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Ale, Srinivasulu and Gowda, Prasanna H. and Mulla, David J. and Moriasi, Daniel N. and Youssef, Mohamed A.}, year={2013}, month={Nov}, pages={21–30} }
 @article{poole_skaggs_cheschier_youssef_crozier_2013, title={Effects of drainage water management on crop yields in North Carolina}, volume={68}, ISSN={["1941-3300"]}, DOI={10.2489/jswc.68.6.429}, abstractNote={Research studies on a wide range of soils, crops, locations, and climates have shown that drainage water management (DWM), or controlled drainage (CD), can be used to substantially reduce the loss of nitrogen (N), and in some cases, phosphorus (P) from drained agricultural lands to surface waters. The adoption and widespread application of DWM depends on a variety of factors including its impact on crop yields. This paper presents results from a long term field study on the effect of DWM or CD on crop yields in a three-crop, two-year corn/wheat–soybean rotation. Yields were measured on replicated field scale plots under CD and conventional or free drainage (FD) treatments for a total of 18 crops on two experimental sites during the period from 1990 to 2011. Data were collected on 7 corn (Zea mays L.) crops, 5 wheat (Triticum aestivum L.) crops, and 6 soybean (Glycine max L.) crops. Controlled drainage had no significant effect on yields of winter wheat, which in North Carolina is grown in the wettest, coolest part of the year. Controlled drainage increased corn yields compared to FD in all seven years. The average yield increase for corn was 11%. Controlled drainage also increased soybean yield in all years with an average increase of 10% compared to FD. Such yield responses will promote the application of DWM, which will result in both economic and environmental benefits.}, number={6}, journal={JOURNAL OF SOIL AND WATER CONSERVATION}, author={Poole, C. A. and Skaggs, R. W. and Cheschier, G. M. and Youssef, M. A. and Crozier, C. R.}, year={2013}, pages={429–437} }
 @misc{tian_youssef_skaggs_chescheir_amatya_2013, title={Predicting dissolved organic nitrogen export from a drained loblolly pine plantation}, volume={49}, ISSN={["1944-7973"]}, DOI={10.1002/wrcr.20157}, abstractNote={Key Points}, number={4}, journal={WATER RESOURCES RESEARCH}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Chescheir, G. M. and Amatya, Devendra M.}, year={2013}, month={Apr}, pages={1952–1967} }
 @misc{amatya_rossi_saleh_dai_youssef_williams_bosch_chescheir_sun_skaggs_et al._2013, title={Review of nitrogen fate models applicable to forest landscapes in the southern US}, volume={56}, DOI={10.13031/trans.56.10096}, abstractNote={Assessing the environmental impacts of fertilizer nitrogen (N) used to increase productivity in managed forests is complex due to a wide range of abiotic and biotic factors affecting its forms and movement. Models developed to predict fertilizer N fate (e.g., cycling processes) and water quality impacts vary widely in their design, scope, and potential appli- cation. We review the applicability of five commonly used eco-hydrologic models (APEX, MIKESHE-DNDC, DRAIN- MOD-FOREST, REMM, and SWAT) in assessing N fate and transport in southern forest landscapes ( 50 km 2 ), although N routing below the subbasin level does not yet exist. Similarly, the dis- tributed MIKESHE-DNDC model has been used to assess N cycles across different spatial scales, on both uplands and lowlands, but was not intended to model lateral N transport. However, MIKESHE alone is capable of describing the hy- drology and N transport. The strengths of each of the models reflect their original design and scope intent. Based on this review, none of the five models that we considered is independently adequate to address the fate of N fertilizers applied to forest stands at both small and large scales, including uplands and lowlands. While efforts are underway to extend these tools' capabilities and address their various limitations, the models must be validated using experimental data before us- ing their outputs, together with uncertainty analysis, for developing forest fertilization guidelines and the fate and transport of N.}, number={5}, journal={Transactions of the ASABE}, author={Amatya, D. M. and Rossi, C. G. and Saleh, A. and Dai, Z. and Youssef, M. A. and Williams, R. G. and Bosch, D. D. and Chescheir, G. M. and Sun, G. and Skaggs, R. W. and et al.}, year={2013}, pages={1731–1757} }
 @article{skaggs_youssef_chescheir_2012, title={A Drainmod-based method to estimate effects of drainage water management on annual nitrogen loss to surface water}, volume={55}, DOI={10.13031/2013.41515}, abstractNote={Effects of drainage water management (DWM) on nitrogen (N) losses to surface waters can be estimated by multiplying the change in subsurface drainage and surface runoff, as predicted by DRAINMOD, by long-term mean nitrogen (N) concentration, which is a function of local site conditions (climate, soil, cropping system, farming practices, and drainage system). Consistent with experimental observations from several sources, this approximate method assumes that the effect of DWM on N losses is proportional to its effect on drainage and surface runoff volumes. The reliability of the method was evaluated by comparing estimated annual N losses for two sites (one in North Carolina and one in Illinois) to those predicted by the process-based nitrogen model DRAINMOD-NII. The long-term N concentrations used in the approximate method were based on DRAINMOD-NII predictions. DRAINMOD-NII simulations predicted that DWM would reduce long-term average N losses to surface waters by 35% for continuous corn (CC) and 33% for a corn-wheat-soybean (CWS) rotation in North Carolina and by 31% and 26% for CC and a corn-soybean (CS) rotation in Illinois. The approximate method estimated the annual effect of DWM on N losses within 3 kg ha-1 of that predicted by DRAINMOD-NII in over 68% of the years for the CWS and CS rotations at both sites and in over 51% of the years for CC. Overestimated effects in some years were balanced by underestimated effects in others. However, relatively large errors occurred in about 25% of the years when N concentrations in the drainage water varied significantly from the long-term average. These errors typically occurred following periods when crop yields deviated significantly from the average. When these outliers were excluded from the analyses, the goodness of fit between annual N losses predicted by DRAINMOD-NII and annual losses estimated by the approximate method was substantially improved (Nash-Sutcliffe EF values ranging from 0.54 to 0.79). Although more research is needed to improve the approximate method when concentrations vary significantly from the long-term average, the results presented herein indicate that the method provides a reliable means of assessing impacts of DWM under normal conditions.}, number={3}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M.}, year={2012}, pages={799–808} }
 @article{skaggs_youssef_chescheir_2012, title={Drainmod: model use, calibration, and validation}, volume={55}, DOI={10.13031/2013.42259}, abstractNote={DRAINMOD is a process-based, distributed, field-scale model developed to describe the hydrology of poorly drained and artificially drained soils. The model is based on water balances in the soil profile, on the field surface, and, in some cases, in the drainage system. This article briefly describes the model and the algorithms that are used to quantify the various hydrologic components. Inputs for soil properties, site parameters, weather data, and crop characteristics required in the application of the model are presented and discussed with respect to their role in calibration. Methods for determining field effective values of key inputs to the model, either independently or as a part of the calibration process, are demonstrated in a case study. The case study involved calibrating DRAINMOD with two years of field data for a subsurface drained agricultural field in eastern North Carolina, followed by testing or validation of the model with two additional years of data. Performance statistics indicated that the model with calibrated input data accurately predicted daily water table depths with Nash-Sutcliffe modeling efficiency (EF) values of 0.68 and 0.72, daily drainage rates (EF = 0.73 and 0.49), and monthly drainage volumes (EF = 0.87 and 0.77) for the two-year validation period.}, number={4}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M.}, year={2012}, pages={1509–1522} }
 @article{ale_bowling_youssef_brouder_2012, title={Evaluation of Simulated Strategies for Reducing Nitrate-Nitrogen Losses through Subsurface Drainage Systems}, volume={41}, ISSN={["0047-2425"]}, DOI={10.2134/jeq2010.0466}, abstractNote={The nitrates (NO(3)-N) lost through subsurface drainage in the Midwest often exceed concentrations that cause deleterious effects on the receiving streams and lead to hypoxic conditions in the northern Gulf of Mexico. The use of drainage and water quality models along with observed data analysis may provide new insight into the water and nutrient balance in drained agricultural lands and enable evaluation of appropriate measures for reducing NO(3)-N losses. DRAINMOD-NII, a carbon (C) and nitrogen (N) simulation model, was field tested for the high organic matter Drummer soil in Indiana and used to predict the effects of fertilizer application rate and drainage water management (DWM) on NO-N losses through subsurface drainage. The model was calibrated and validated for continuous corn (Zea mays L.) (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation treatments separately using 7 yr of drain flow and NO(3)-N concentration data. Among the treatments, the Nash-Sutcliffe efficiency of the monthly NO(3)-N loss predictions ranged from 0.30 to 0.86, and the percent error varied from -19 to 9%. The medians of the observed and predicted monthly NO(3)-N losses were not significantly different. When the fertilizer application rate was reduced ~20%, the predicted NO(3)-N losses in drain flow from the CC treatments was reduced 17% (95% confidence interval [CI], 11-25), while losses from the CS treatment were reduced by 10% (95% CI, 1-15). With DWM, the predicted average annual drain flow was reduced by about 56% (95% CI, 49-67), while the average annual NO(3)-N losses through drain flow were reduced by about 46% (95% CI, 32-57) for both tested crop rotations. However, the simulated NO(3)-N losses in surface runoff increased by about 3 to 4 kg ha(-1) with DWM. For the simulated conditions at the study site, implementing DWM along with reduced fertilizer application rates would be the best strategy to achieve the highest NO(3)-N loss reductions to surface water. The suggested best strategies would reduce the NO(3)-N losses to surface water by 38% (95% CI, 29-46) for the CC treatments and by 32% (95% CI, 23-40) for the CS treatments.}, number={1}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Ale, Srinivasulu and Bowling, Laura C. and Youssef, Mohamed A. and Brouder, Sylvie M.}, year={2012}, month={Jan}, pages={217–228} }
 @article{tian_youssef_skaggs_amatya_chescheir_2012, title={Modeling water, carbon, and nitrogen dynamics for two drained pine plantations under intensive management practices}, volume={264}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2011.09.041}, abstractNote={This paper reports results of a study to test the reliability of the DRAINMOD-FOREST model for predicting water, soil carbon (C) and nitrogen (N) dynamics in intensively managed forests. The study site, two adjacent loblolly pine (Pinus taeda L.) plantations (referred as D2 and D3), are located in the coastal plain of North Carolina, USA. Controlled drainage (with weir and orifice) and various silvicultural practices, including nitrogen (N) fertilizer application, thinning, harvesting, bedding, and replanting, were conducted on the study site. Continuous collection of hydrological and water quality data (1988–2008) were used for model evaluation. Comparison between predicted and measured hydrologic variables showed that the model accurately predicted long-term subsurface drainage dynamics and water table fluctuations in both loblolly pine plantations. Predicted mean and standard deviation of annual drainage matched measured values very well: 431 ± 217 vs. 436 ± 231 mm for D2 site and 384 ± 152 vs. 386 ± 160 mm for D3 site. Nash–Sutcliffe coefficients (NSE) were above 0.9 for drainage predictions on annual and monthly basis and above 0.86 for predictions of daily water table fluctuations. Compared to measurements in other similar studies, the model also reasonably estimated long-term dynamics of organic matter pools on forest floor and in forest soil. Predicted mean and standard deviation of annual nitrate exports were comparable to measured values: 1.6 ± 1.3 vs. 1.5 ± 1.5 kg ha−1 for D2 site, and 1.4 ± 1.3 vs. 1.3 ± 1.1 kg ha−1 for D3 site, respectively. Predicted nitrate export dynamics were also in excellent agreement with field measurements as indicated by NSE above 0.90 and 0.84 on annual and monthly bases, respectively. The model, thus successfully tested, was applied to predicted hydrological and biogeochemical responses to drainage water management and silvicultural practices. Specifically, the model predicted reduced rainfall interception and ET after clear cutting, both of which led to increased water yield and elevated water table, as expected. The model also captured temporary changes in nitrogen transformations following forest harvesting, including increased mineralization, nitrification, denitrification, and decreased plant uptake. Overall, this study demonstrated that DRAINMOD-FOREST can predict water, C and N dynamics in drained pine forests under intensive management practices.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Amatya, Devendra M. and Chescheir, George M.}, year={2012}, month={Jan}, pages={20–36} }
 @article{tian_youssef_skaggs_amatya_chescheir_2012, title={Temporal Variations and Controlling Factors of Nitrogen Export from an Artificially Drained Coastal Forest}, volume={46}, ISSN={["1520-5851"]}, DOI={10.1021/es3011783}, abstractNote={Nitrogen losses in drainage water from coastal forest plantations can constrain the long term sustainability of the system and could negatively affect adjacent nutrient sensitive coastal waters. Based on long-term (21 years) field measurements of hydrology and water quality, we investigated the temporal variations and controlling factors of nitrate and dissolved organic nitrogen (DON) export from an artificially drained coastal forest over various time scales (interannual, seasonal, and storm events). According to results of stepwise multiple linear regression analyses, the observed large interannual variations of nitrate flux and concentration from the drained forest were significantly (p < 0.004) controlled by annual mean water table depth, and annual drainage or precipitation. Annual precipitation and drainage were found to be dominant factors controlling variations of annual DON fluxes. Temporal trends of annual mean DON concentration could not be explained explicitly by climate or hydrologic factors. No significant difference was observed between nitrogen (both nitrate and DON) export during growing and nongrowing seasons. Nitrate exhibited distinguished export patterns during six selected storm events. Peak nitrate concentrations during storm events were significantly (p < 0.003) related to 30-day antecedent precipitation index and the minimum water table depth during individual events. The temporal variations of DON export within storm events did not follow a clear trend and its peak concentration during the storm events was found to be significantly (p < 0.006) controlled by the short-term drying and rewetting cycles.}, number={18}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Amatya, Devendra M. and Chescheir, George M.}, year={2012}, month={Sep}, pages={9956–9963} }
 @article{skaggs_youssef_gilliam_evans_2010, title={Effect of controlled drainage on water and nitrogen balances in drained lands}, volume={53}, DOI={10.13031/2013.35810}, abstractNote={Field studies have shown that subsurface drainage systems can be managed to conserve water and reduce losses of nitrogen (N) to surface waters. The practice, called controlled drainage (CD) or drainage water management (DWM), is a viable alternative for reducing N loads from drained cropland, including millions of acres in the Midwest. This article reviews past studies on the effect of CD on drainage volumes and N losses for a wide range of soils and climatological conditions and uses simulations to examine mechanisms affecting the practice. Results published in the literature show that CD has reduced drainage volumes and N losses in drainage waters by 17% to over 80%, depending on soil properties, crops, drainage intensities, control strategies, and location. This study resulted in the following conclusions. CD reduces subsurface drainage and raises water tables, while increasing ET, seepage, and surface runoff. Seepage, which depends on soil properties and site conditions, is an important factor that often governs the effectiveness of CD. Experiments to determine the effect of CD on drainage volumes and N losses should be conducted on the field or watershed scale so that impacts of seepage are properly represented. Increases in ET in response to CD are important but are rarely greater than 10%. The effect of this increase in water use on drainage water loss is also less than 10% for most locations. CD reduces N losses in drainage water by about the same percentage as its effect on subsurface drainage volume in most cases. The effect of CD on N loss to surface waters depends on denitrification, both in the profile and in reduced zones along seepage paths. For soils that do not develop reduced zones, the effect of CD on N loss may be substantially less than its effect on drainage volume.}, number={6}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Gilliam, J. W. and Evans, R. O.}, year={2010}, pages={1843–1850} }
 @article{luo_sands_youssef_strock_song_canelon_2010, title={Modeling the impact of alternative drainage practices in the northern Corn-belt with DRAINMOD-NII}, volume={97}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2009.10.009}, abstractNote={The hydrologic and water quality impacts of subsurface drainage design and management practices are being investigated through field and simulation studies throughout the northern Corn-belt. Six years of data from an ongoing field study in south central Minnesota (Sands et al., 2008) were used to support a modeling effort with DRAINMOD-NII to investigate: (1) the performance of the model in a region where soils are subject to seasonal freeze–thaw and (2) the long-term hydrologic and water quality characteristics of conventional and alternative subsurface drainage practices. Post-calibration model prediction and efficiency were deemed satisfactory using standard model performance criteria. Prediction errors were primarily associated with early spring snowmelt hydrology and were attributed to the methods used for simulating snow accumulation and melting processes, in addition to potential sublimation effects on ET estimates. Long-term simulations with DRAINMOD-NII indicated that drainage design and/or management practices proposed as alternatives to conventional design may offer opportunities to reduce nitrate (NO3)-nitrogen losses without significantly decreasing (and in some cases, increasing) crop yields for a Webster silty clay loam soil at Waseca, Minnesota. The simulation study indicated that both shallow drainage and controlled drainage may reduce annual drainage discharge and NO3-nitrogen losses by 20–30%, while impacting crop yields from −3% (yield decrease) to 2%, depending on lateral drain spacing. The practice of increasing drainage intensity (decreasing drain spacing) beyond recommended values appears to not significantly affect crop yield but may substantially increase drainage discharge and nitrate-nitrogen losses to surface waters.}, number={3}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Luo, W. and Sands, G. R. and Youssef, M. and Strock, J. S. and Song, I. and Canelon, D.}, year={2010}, month={Mar}, pages={389–398} }
 @article{thorp_youssef_jaynes_malone_ma_2009, title={DRAINMOD-N II: Evaluated for an agricultural system in Iowa and compared to RZWQM-DSSAT}, volume={52}, DOI={10.13031/2013.29144}, abstractNote={A new simulation model for N dynamics, DRAINMOD-N II, has been previously evaluated for only a few sites. We evaluated the model using ten years (1996-2005) of measured data from a subsurface-drained, corn-soybean agricultural system near Story City, Iowa. Nitrogen fertilizer was applied to plots at low, medium, and high rates (57 to 67 kg N ha-1, 114 to 135 kg N ha-1, and 172 to 202 kg N ha-1, respectively) during corn years, and nitrate (NO3) losses from subsurface drains under each plot were monitored biweekly for ten years. Average annual simulated and measured NO3 losses in drainage water were 21.9 and 20.1 kg N ha-1 for the low N rate, 26.6 and 26.5 kg N ha-1 for the medium N rate, and 36.6 and 37.0 kg N ha-1 for the high N rate, respectively. The model efficiency statistics for DRAINMOD-N II simulations of annual subsurface drain NO3 losses were 0.89, 0.95, and 0.94 for the low, medium, and high N rates, respectively. For the same experimental dataset, a comparison of DRAINMOD-N II simulations to that of another model that simulates hydrologic and N dynamics of agricultural systems, the RZWQM-DSSAT hybrid model, demonstrated that the two models were most different in their simulations of soybean N fixation, plant N uptake, and net N mineralization. Future field investigations should focus on generating better understandings of these processes. The results suggest that DRAINMOD-N II can reasonably simulate the effects of different corn-year N rates on losses of NO3 through subsurface drainage lines and that simulations of subsurface drainage NO3 losses by DRAINMOD-N II are comparable to that of RZWQM-DSSAT.}, number={5}, journal={Transactions of the ASABE}, author={Thorp, K. R. and Youssef, M. A. and Jaynes, D. B. and Malone, R. W. and Ma, L.}, year={2009}, pages={1557–1573} }
 @article{salazar_wesstrom_youssef_skaggs_joel_2009, title={Evaluation of the DRAINMOD-N II model for predicting nitrogen losses in a loamy sand under cultivation in south-east Sweden}, volume={96}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2008.08.008}, abstractNote={The DRAINMOD–N II model (version 6.0) was evaluated for a cold region in south-east Sweden. The model was field-tested using four periods between 2002 and 2004 of climate, soil, hydrology and water quality data from three experimental plots, planted to a winter wheat–sugarbeet–barley–barley crop rotation and managed using conventional and controlled drainage. DRAINMOD–N II was calibrated using data from a conventional drainage plot, while data sets from two controlled drainage plots were used for model validation. The model was statistically evaluated by comparing simulated and measured drain flows and nitrate–nitrogen (NO3–N) losses in subsurface drains. Soil mineral nitrogen (N) content was used to evaluate simulated N dynamics. Observed and predicted NO3–N losses in subsurface drains were in satisfactory agreement. The mean absolute error (MAE) in predicting NO3–N drainage losses was 0.16 kg N ha−1 for the calibration plot and 0.21 and 0.30 kg N ha−1 for the two validation plots. For the simulation period, the modelling efficiency (E) was 0.89 for the calibration plot and 0.49 and 0.55 for the validation plots. The overall index of agreement (d) was 0.98 for the calibration plot and 0.79 and 0.80 for the validation plots. These results show that DRAINMOD–N II is applicable for predicting NO3–N losses from drained soil under cold conditions in south-east Sweden.}, number={2}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Salazar, Osvaldo and Wesstrom, Ingrid and Youssef, Mohamed A. and Skaggs, R. Wayne and Joel, Abraham}, year={2009}, month={Feb}, pages={267–281} }
 @article{david_del grosso_hu_marshall_mcisaac_parton_tonitto_youssef_2009, title={Modeling denitrification in a tile-drained, corn and soybean agroecosystem of Illinois, USA}, volume={93}, ISSN={["0168-2563"]}, DOI={10.1007/s10533-008-9273-9}, number={1-2}, journal={BIOGEOCHEMISTRY}, author={David, Mark B. and Del Grosso, Stephen J. and Hu, Xuetao and Marshall, Elizabeth P. and McIsaac, Gregory F. and Parton, William J. and Tonitto, Christina and Youssef, Mohamed A.}, year={2009}, month={Mar}, pages={7–30} }
 @article{ale_bowling_brouder_frankenberger_youssef_2009, title={Simulated effect of drainage water management operational strategy on hydrology and crop yield for Drummer soil in the Midwestern United States}, volume={96}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2008.10.005}, abstractNote={The hypothetical effects of drainage water management operational strategy on hydrology and crop yield at the Purdue University Water Quality Field Station (WQFS) were simulated using DRAINMOD, a field-scale hydrologic model. The WQFS has forty-eight cropping system treatment plots with 10 m drain spacing. Drain flow observations from a subset of the treatment plots with continuous corn (Zea mays L.) were used to calibrate the model, which was then used to develop an operational strategy for drainage water management. The chosen dates of raising and lowering the outlet during the crop period were 10 and 85 days after planting, respectively, with a control height of 50 cm above the drain (40 cm from the surface). The potential effects of this operational strategy on hydrology and corn yield were simulated over a period of 15 years from 1991 to 2005. On average, the predicted annual drain flows were reduced by 60% (statistically significant at 95% level). This is the most significant benefit of drainage water management since it may reduce the nitrate load to the receiving streams. About 68% of the reduced drain flow contributed to an increase in seepage. Drainage water management increased the average surface runoff by about 85% and slightly decreased the relative yield of corn crop by 0.5% (both are not statistically significant at 95% level). On average, the relative yield due to wet stress (RYw) decreased by 1.3% while relative yield due to dry stress (RYd) increased by 1%. Overall, the relative crop yield increased in 5 years (within a range of 0.8–6.9%), decreased in 8 years (within a range of 0.2–5.5%), and was not affected in the remaining 2 years. With simulated drainage water management, the water table rose above the conventional drainage level during both the winter and the crop periods in all years (except 2002 crop season). The annual maximum winter period rise ranged between 47 cm (1995) and 87 cm (1992), and the annual maximum crop period rise ranged between no effect (2002) and 47 cm (1993).}, number={4}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Ale, S. and Bowling, L. C. and Brouder, S. M. and Frankenberger, J. R. and Youssef, M. A.}, year={2009}, month={Apr}, pages={653–665} }
 @article{bechtold_koehne_youssef_lennartz_skaggs_2007, title={Simulating nitrogen leaching and turnover in a subsurface-drained grassland receiving animal manure in Northern Germany using DRAINMOD-N II}, volume={93}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2007.06.001}, abstractNote={The primary objective of this study was to evaluate the nitrogen fate and transport simulation model DRAINMOD-N II for drained permanent grassland soils. Since the plant component of DRAINMOD-N II was developed for annual row crop systems, it was modified using an empirical approach to consider perennial grasses. The model was field-tested using a 12-year (1989–2000) data set of field hydrology, non-reactive tracer transport, and carbon (C) and nitrogen (N) dynamics from a tile drained grassland research site (Infeld, North-West Germany). Model calibration was performed using the first half of the data set, followed by validation using the second half. Model simulations were visually and statistically compared to field measurements. Modified DRAINMOD-N II successfully predicted drain flow during the validation period. The model could also simulate the observed dynamics of weakly preferential tracer transport by using a high longitudinal dispersivity. Furthermore, the model well described organic carbon (OC) dynamics during calibration. Since there were no OC measurements during the second half of the study, OC model predictions were not validated. Simulated and measured N losses via drain flow were in agreement during model calibration. The model, however, substantially under-predicted N loads during the validation period. Two reasons were hypothesized for the relatively poor performance of DRAINMOD-N II during the validation period. First, the simplistic approach used in the modified DRAINMOD-N II to quantify grass biomass yield did not take into account the effect of soil water dry or wet stresses on plant growth and biomass yield. This hypothesis could not be tested since there were no measurements of grass biomass yield. Secondly, the effect of the calibration errors in N process rates increased with the difference in precipitation patterns between the calibration and validation periods. This is despite the fact that calibrated transformation rates were within published ranges. While inconclusive, these results indicates that a more robust approach for quantifying grass biomass and N uptake may be needed for the current version of DRAINMOD-N II in order to successfully simulate C and N dynamics in drained grassland.}, number={1-2}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Bechtold, Iris and Koehne, Sigrid and Youssef, Mohamed A. and Lennartz, Bernd and Skaggs, R. Wayne}, year={2007}, month={Oct}, pages={30–44} }
 @article{skaggs_youssef_chescheir_2006, title={Drainage design coefficients for eastern United States}, volume={86}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2006.06.007}, abstractNote={The development of drainage simulation models has made it possible to quantitatively describe the performance of drainage systems, including the effects of design parameters on yields. While this was a primary goal of drainage researchers 40 years ago, it is no longer sufficient. Currently, the effect of drainage on nutrient loads and surface water quality is of equal or greater importance to production goals. Limited field data and modeling results indicate that nitrogen (N) loss in drainage water is proportional to subsurface drainage intensity (DI). This implies that the drainage system should be tailored to soil and site conditions, such that the DI is as small as possible. While simulation models can be used to determine drain depth and spacing required to maximize yields or profits for a specific site, the modeling expertise and/or the extensive data required are often not available. Simple approaches are still needed for estimating drain spacing and depth. The Hooghoudt equation has been used for many years for this purpose. Its application requires knowledge of the design drainage rate, which has not been defined for many locations in the US. A simulation study was conducted to determine the drain spacing corresponding to predicted maximum economic return for corn production on four soils at 10 locations in eastern United States. The drainage intensity (cm/day) corresponding to the optimum drain spacing was defined as the design drainage rate (DDR). DDR varied with growing season rainfall and ranged from an average (across the four soils) of 0.58 cm/day at Toledo, OH to 1.61 cm/day at Baton Rouge, LA. Variation of DDR among the four soils was least for the low rainfall locations and highest where growing season rainfall was high. The regression equation, DDR = 0.004P − 1.1, may be used to estimate DDR (cm/day) in terms of growing season rainfall, P (mm). These results were obtained for a drain depth of 1 m and surface depressional storage of 2 cm. Additional research is needed to test the relationships, and/or develop new equations, for additional drain depths and surface storages.}, number={1-2}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Skaggs, R. Wayne and Youssef, M. A. and Chescheir, G. M.}, year={2006}, month={Nov}, pages={40–49} }
 @article{youssef_skaggs_chescheir_gilliam_2006, title={Field evaluation of a model for predicting nitrogen losses from drained lands}, volume={35}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2005.0249}, abstractNote={ABSTRACT}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Youssef, Mohamed A. and Skaggs, R. Wayne and Chescheir, George M. and Gilliam, J. Wendell}, year={2006}, pages={2026–2042} }
 @inproceedings{youssef_skaggs_2006, title={The Nitrogen Simulation Model, DRAINMOD-N II: Field Testing and Model Application for Contrasting Soil Types and Climatological Conditions}, ISBN={9780784408568}, url={http://dx.doi.org/10.1061/40856(200)304}, DOI={10.1061/40856(200)304}, abstractNote={DRAINMOD-N II is a field-scale, process-based model that simulates nitrogen dynamics and turnover in drained croplands under different management practices and soil and environmental condition. This paper summarizes results of testing the model using data sets from two drained agricultural sites with contrasting soils, climatic conditions, and management practices. One site is located in North Carolina and the other site is located in Indiana. It also summarizes results of long term simulations conducted using calibrated model inputs to study the effects of drainage design and management and N fertilization rates on NO3-N leaching losses under the local soil and climatic conditions of each site. Results of the two field evaluations indicated that the model accurately predicted annual and cumulative NO3-N losses from both sites. Model predictions for the IN site were more accurate than model predictions for the NC site. Results of the long term simulation studies demonstrated the strong influence of the N fertilization rates on N losses from drained croplands. It also indicated the influence of drainage design (drain depth and spacing) and management (drainage control) on N leaching losses. The predicted response of the soil-water-plant system at each site to different drainage water and N fertilization scenarios was influenced by local soil and climatic conditions. These results indicated that DRAINMOD-N II can be reliably used in the development and evaluation of drainage water and agronomic management practices that reduce N losses from drained agricultural lands.}, booktitle={World Environmental and Water Resource Congress 2006}, publisher={American Society of Civil Engineers}, author={Youssef, M. A. and Skaggs, R. W.}, year={2006}, month={May} }
 @article{skaggs_youssef_chescheir_gilliam_2005, title={Effect of drainage intensity on nitrogen losses from drained lands}, volume={48}, DOI={10.13031/2013.20103}, abstractNote={Agricultural drainage is a primary source of excessive nitrogen (N) in surface waters, leading to significant water 
quality problems in streams and estuaries in many locations around the world. Although there have been only a few field 
studies of the effect of drain depth and spacing on N loss to surface waters, the data that exist indicate that N loss increases 
as subsurface drains are placed closer together. Some simulation model studies agree with these trends, others do not. 
Published field data from Indiana and North Carolina were plotted as a function of drainage intensity (DI), which was defined 
as the steady-state drainage rate when the water table at a point midway between the drains is coincident with the surface. 
Trends for NO3-N loss as a function of DI were similar for soils in the two states in spite of large differences in weather and 
soil conditions. These data indicated that the magnitude of NO3-N loss in drainage waters is strongly dependent on DI. 
Simulations were conducted to examine effects of drain depth, spacing, and soil properties on processes that affect NO3-N 
loss from drained soils. The use of DI explained or normalized the effect of these variables on some of the processes but not 
others. Results showed that, in addition to its effect on DI, drain depth appears to have a significant impact on NO3-N losses.}, number={6}, journal={Transactions of the ASAE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M. and Gilliam, J. W.}, year={2005}, pages={2169–2177} }
 @article{wang_youssef_skaggs_atwood_frankenberger_2005, title={Sensitivity analyses of the nitrogen simulation model, DRAINMOD-N II}, volume={48}, DOI={10.13031/2013.20106}, abstractNote={A two-step global sensitivity analysis was conducted for the nitrogen simulation model DRAINMOD-N II to assess 
the sensitivity of model predictions of NO3-N losses with drainage water to various model inputs. Factors screening using 
the LH-OAT (Latin hypercube sampling - one at a time) sensitivity analysis method was performed as a first step considering 
48 model parameters; then a variance-based sensitivity analysis was conducted for 20 model parameters, which were the 
parameters ranked 1 to 14 by the LH-OAT method, five organic carbon (OC) decomposition parameters, and the empirical 
shape factor of the temperature response function for the nitrification process. DRAINMOD-N II simulated a continuous corn 
production on a subsurface drained sandy loam soil using a 40-year (1951-1990) eastern North Carolina climatological 
record. Results from the first 20-year period of the simulations were used to initialize the soil organic matter pools, and results 
from the last 20-year period of the simulations were considered for the sensitivity analyses. Both yearly and 20-year average 
model predictions of NO3-N losses through drainage flow were used in the analyses. Both sensitivity analysis methods 
indicated that DRAINMOD-N II is most sensitive to denitrification parameters, especially those controlling temperature 
effect on process rate. Results also indicated that the model is mildly sensitive to the parameters controlling OC decomposition 
and associated N mineralization/immobilization. The use of different sensitivity analysis methods with dissimilar theoretical 
foundations increases the confidence in key parameters identification. More efforts should be focused on quantifying key 
parameters for more accurate model predictions.}, number={6}, journal={Transactions of the ASAE}, author={Wang, X. and Youssef, M. A. and Skaggs, R. W. and Atwood, J. D. and Frankenberger, J. R.}, year={2005}, pages={2205–2212} }
 @article{youssef_skaggs_chescheir_gilliam_2005, title={The  nitrogen simulation model, DRAINMOD-N II}, volume={48}, DOI={10.13031/2013.18335}, abstractNote={DRAINMOD-N II is a field-scale, process-based model that was developed to simulate nitrogen dynamics and 
turnover in the soil-water-plant system under different management practices and soil and environmental conditions. It is 
an enhanced version of the nitrogen (N) simulation model, DRAINMOD-N, that simulates a more complete N cycle, adds a 
carbon (C) cycle, and operates at different levels of complexity. Processes considered in the model include atmospheric 
deposition, application of mineral N fertilizers including urea and anhydrous ammonia (NH3), soil amendment with organic 
N (ON) sources including plant residues and animal waste, plant uptake, organic C (OC) decomposition and associated N 
mineralization/immobilization, nitrification, denitrification, NH3 volatilization, and N losses via subsurface drainage and 
surface runoff. Nitrogen pools considered in the model are nitrate-nitrogen (NO3-N), ammoniacal nitrogen (NHx-N) and ON. 
DRAINMOD-N II includes a submodel that simulates C dynamics in the soil-plant system using a C cycle similar to that of 
the CENTURY model. A simplified approach is used to simulate temporal changes in soil pH; consequently, the model 
determines the composition of the NHx-N pool and, if necessary, changes its operation mode. DRAINMOD-N II simulates 
N reactive transport using a finite difference solution to a multiphase form of the one-dimensional advection- 
dispersion-reaction equation. Model output includes daily concentrations of NO3-N and NHx-N in soil solution and drain 
flow, daily OC content of the top 20 cm soil layer, and cumulative rates of simulated N processes.}, number={2}, journal={Transactions of the ASAE}, author={Youssef, M. A. and Skaggs, R. W. and Chescheir, G. M. and Gilliam, J. W.}, year={2005}, pages={611–626} }