Subsurface drainage is needed for maintaining good crop yields in poorly drained lands, mitigating water stress, ensuring field trafficability, and timely agronomic operations. However, it can lead to water quality issues by providing faster routes for nutrients to leave the field resulting in more nitrate loading. Saturated buffers (SB) are conservation drainage practices aimed at reducing nitrate loss. By redirecting a portion of the drainage discharge through vegetative buffers, nitrate is mainly removed via denitrification. Yet, reported effectiveness varies, necessitating a consistent design approach. Current literature is limited, primarily focusing on Iowa and Illinois. Therefore, there's a need for broader understanding of the SB hydrology and nitrate loading functionality. Better understanding can aid in proposing design and management guidelines to enhance SB performance.We developed a new SB design approach incorporating site-specific conditions to determine the optimal buffer width. Using process-based modeling, we estimated nitrate load removal iteratively across various buffer widths. Performance comparisons with existing SB design approaches utilized modeling and field data from two Michigan sites. SB parameters (buffer width and distribution pipe length) and field data inputs were used to estimate diverted flow and nitrate load removal for each design. Comparison revealed that designs 2 and 3 were equally effective, yielding higher nitrate load removal (20%) than Design 1. Maximizing diverted flow didn't improve nitrate removal, emphasizing the need to target maximum nitrate load removal directly while considering site-specific characteristics. We developed a DRAINMOD-based decision-support tool for SBs (DBDSTSB), to incorporate the new design approach and facilitate its use. Moreover, we validated its prediction performance of the flow and nitrate load parameters utilizing published evaluation criteria of standard statistical indicators and measured data from two fields in Iowa. The DBDSTSB showed “good” performance in predicting annual field drainage, diverted flow to buffer, nitrate load in drainage, and nitrate load removal by SB. The DBDSTSB’s predictions of the long-term average annual percentages of diverted flow and nitrate load removal were also reasonable, where their deviations from the corresponding measured values amounted to only 1% and 2%, respectively. We conducted an SB field study to assess the stacked CD+SB system's performance and component contributions in reducing drainage discharge and nitrate loading from tiled agricultural fields. The study, from Jun 2019 to Feb 2024 in Michigan, employed a paired-field approach. The stacked CD+SB system notably reduced drainage discharge and nitrate load of free drainage (FD) by annual averages of 43.1% and 83.4%, respectively. The CD component played a major role in these reductions (44.1% and 82.5%, respectively). Conversely, the SB only slightly contributed to overall nitrate load reduction (0.9%). Mild management of the stoplogs, with depths greater than 50 cm, caused backflow and additional nitrate load from the SB. Conversely, intense management, with depths around 30 cm, limited the backflow volume. In conclusion, DBDSTSB facilitates the new design's use and provides credible quantification of SB performance. This can support nitrate trading programs, promoting SB adoption for enhanced nitrate removal. Stacking SB with CD and employing intense management has the potential to improve nitrate removal performance.
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