Combining in-field and edge-of-field practices enhances nitrate reduction in tile-drained catchments

Tile drainage systems enhance agricultural productivity in poorly drained regions but also increase nitrate export, posing serious water quality challenges. This study employs the DLEM-catchment model to assess the effectiveness of in-field and edge-of-field practices in reducing nitrate loading across four tile-drained catchments in the U.S. Corn Belt. Simulated in-field practices include cover crops, crop rotation, fertilizer input reductions, and optimized fertilizer timing, while edge-of-field measures focus on saturated riparian buffers (SRBs) and water quality wetlands (WQWs). Results show that cover crops and 10-20 % fertilizer reductions are effective in-field strategies, reducing nitrate loading by 10.5 % and 6.2-12.8 %, respectively. Combining cropping system changes (e.g., cover crops or crop rotation) with fertilizer reductions produced the largest nitrate reductions, while fertilizer reductions combined with optimized application timing provided the most favorable balance between nitrate mitigation and minimal yield penalty. SRBs provided only minor catchment-scale improvements due to limited interception area, reducing nitrate loads by an additional 0.5 %, although nitrate removal within the intercepted drainage area reached 19.9 %. In contrast, WQWs are simulated to reduce nitrate loading by an additional 28.3 % on average across the four catchments because of longer water residence times and enhanced biogeochemical processes. These results demonstrate that integrating in-field nutrient management with edge-of-field interception offers the greatest potential for sustained nitrate reduction. The variability in responses across catchments highlights the importance of site-specific, integrated management strategies that combine source reduction with downstream interception to improve water quality while sustaining crop productivity, consistent with emerging precision conservation frameworks.