LAUSR

Growing annual crops such as corn can lead to considerable nutrient losses through subsurface drainage in agricultural fields, posing a serious threat to surface water quality in the Midwest U.S. Perennial crops have the potential to reduce these nutrient losses. However, more comprehensive data are needed on the nutrient loss effect of perennial crops. We examined the effect of alfalfa (Medicago sativa L.) on nitrate-nitrogen (NO3 - -N), total nitrogen (TN), dissolved reactive phosphorus (DRP), and total phosphorus (TP) in subsurface drainage using a Before-After-Control-Impact (BACI) experimental design with one control field (annual crops) and one impact field (with alfalfa) each on two farms (site A and B) located in northwest Ohio. The before period (prior to planting alfalfa at the impact field) extended for four years (2013-2017) at site A and six years (2011-2017) at site B, then the after period extended for an additional two years at both sites Reductions in the mean monthly discharge and loads of NO3 - -N, TN, DRP, and TP were significant at site A, while the only significant change at site B was a reduction in the mean monthly TP load. Significant reductions in NO3 - -N loads were observed during spring and winter at site A. In addition, alfalfa also reduced the variability of discharge and nutrient loads through subsurface drainage at both sites. Our findings suggest that introducing alfalfa into annual crop rotations has the potential to reduce subsurface nutrient loads and increase the resiliency of agricultural systems. This article is protected by copyright. All rights reserved.