Cover Crops and Landscape Position Effects on Nitrogen Dynamics in Plant-Soil-Water Pools

Nitrogen dynamics and water quality benefits deriving from the use of cover crops (CCs) are mostly incurred from plot-scale studies without incorporating large-scale variability that is induced by landscape positions. Our understanding of how topography affects the N response in CC systems is limited. The objectives of this study were to evaluate the effects of topography (shoulder, backslope, and footslope) and CCs (cereal rye, Secale cereale L. and hairy vetch, Vicia villosa L.) on nitrogen (N) uptake, soil inorganic N content (nitrate-N, NO3-N and total N, TN), and N leaching in watersheds that were planted with or without CCs. The crop rotation in CC watersheds was corn (Zea mays L.)-cereal rye-soybean (Glycine max L.)-hairy vetch whereas control watersheds had corn-no CC-soybean-no CC rotation. Data from the watersheds was collected for three cash crop seasons and three CC seasons from 2015 to 2018. Nitrogen uptake of hairy vetch in CC watersheds was 110.9, 85.02, and 44.89 kg ha−1 higher at the shoulder, backslope, and footslope positions, when compared to shoulder, backslope, and footslope positions of no CC watersheds. About 12 to 69% reduction in soil solution NO3-N and TN was observed with cereal rye CC when compared to no CCs watersheds. However, reductions in soil solution N concentrations were only seen at the footslope position where the hairy vetch reduced NO3-N and TN concentrations by 7.71 and 8.14 mg L−1 in CC watersheds compared to no CC watersheds. During the corn and soybean growing seasons, similar reductions in soil solution N concentration were only seen at the footslope position in the CC watersheds. The excessive N at footslope positions of CC watersheds may have been fixed in CC biomass, immobilized, or lost through denitrification stimulated by higher water availability at the footslope position. The results of this research can help farmers and stakeholders to make decisions that are site-specific and topographically driven for the management of CCs in row-cropped systems.