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Title:Evaluating effects of water quality BMPs on nitrate-nitrogen losses and crop yield at field and watershed scales
Author(s):Singh, Shailendra
Director of Research:Bhattarai, Rabin
Doctoral Committee Chair(s):Bhattarai, Rabin
Doctoral Committee Member(s):Cooke, Richard; Chu, Maria; Pittelkow, Cameron Mark; Markus, Momcilo
Department / Program:Engineering Administration
Discipline:Agricultural & Biological Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Hydrology, Water quality, Nitrate-N, Field scale, Watershed scale, Yield, BMPs
Abstract:Nitrate-nitrogen (NO3-N) transport from agricultural lands is a major source of surface water pollution in the Midwestern United States. The majority of highly productive agricultural lands in the Midwest region uses subsurface tile drainage to improve crop productivity. However, subsurface tile drainage provides preferential pathways that transfer contaminated water directly to surface water bodies without this water being subjected to soil processes that attenuate NO3-N concentrations. The purpose of this study was to evaluate the long-term impact of different in-field management practices on NO3-N losses and crop production at both field and watershed scales using water quality models. At first, we reviewed 20 years of modeling studies conducted using different field-scale models to assess the effect of various agricultural management practices on NO3-N losses and crop yield and the models' ability to quantify complex processes accurately. Based on our review, we determined two field-scale models: DRAINMOD-DSSAT and RZWM2, suit our research need. We evaluated DRAINMOD-DSSAT using eight years of field observed data from randomly tile-drained, corn-soybean agricultural systems near Danville, central Illinois. The model performed well in simulating field water balance, N balance, and crop yield for both calibration and validation periods. 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. Further, we compared DRAINMOD-DSSAT and RZWQM2 to determine how accurately both models predict hydrology, NO3-N, and crop yield. Our model comparison results showed that both models could simulate field water balance, N balance, and crop yield satisfactorily. The long-term simulation comparison results showed that both the models provided the same conclusion on the effects of N management strategies on NO3-N losses and crop yield, but they differ in quantity. We used RZWQM2 model to evaluate the combined effects of water quality best management practices (BMPs) on tile drainage NO3-N losses and crop yield in a continuous corn system. The model was calibrated and validated using observed data from the Dudley Smith Initiative (DSI) project research site located in Christian County, central Illinois. We calibrated and validated the RZWQM2 model satisfactorily and used it to evaluate long-term impacts of field implemented BMPs using 30-years historical weather data. Based on our long-term evaluation, we found that a 10% reduction in the current N application rate of 224 kg N ha-1 could reduce NO3-N losses by 25-32% without negatively impacting corn yield in 4R and cover crop+4R treatments compared to the conventional method, suggesting further room for N rate optimization. In addition, we scaled up DSI implemented management practices to quantify the impacts on water quality and crop yield at watershed scale using SWAT+ model. The model was calibrated and validated for Upper Sangamon River watershed in central Illinois using 14 years of climate, streamflow, riverine NO3-N, and county-level crop yield data. The model performance for calibration and validation periods ranged from good to very good. The long-term simulation over the period of 30-years showed a reduction of NO3-N load by up to 32% without impacting crop yield. The results suggest that reducing the current N application rate by 20% (i.e., from 224 kg N ha-1 to 179 kg N ha-1) and using 40:60 split N application between spring pre-plant and side-dressing combined with cereal rye as a cover crop in corn-soybean rotation can significantly benefit in minimizing NO3-N losses without losing crop production goals. This study will help researchers and stakeholders in making agricultural decisions beneficial in off-setting environmental impacts and achieving production goals.
Issue Date:2021-11-22
Rights Information:Copyright 2021 Shailendra Singh
Date Available in IDEALS:2022-04-29
Date Deposited:2021-12

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