Nitrate Leaching as Influenced by Cover Cropping and Nitrogen Source

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Abstract
To minimize groundwater contamination by NO−3 and to maximize efficient crop N use, it is necessary to better characterize NO−3 leaching in various cropping systems. Our objectives were to compare the contributions of hairy vetch (Vicia villosa Roth) and NH+4 N sources to NO−3 leaching in corn (Zea mays L.) production, and to compare NO−3 leaching losses in a corn production system utilizing hairy vetch as a N source and winter cover crop with leaching losses in one utilizing an NH+4 N source and a rye (Secale cereale L.) cover crop. Nitrogen, sometimes enriched with 15N, was applied to corn grown on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) in lysimeters as vetch‐ or NH+4‐N at rates between 10.5 and 14.0 g N m−2 yr−1. Treatments (N source/cover crop) were: NH+4‐N/fallow, vetch‐N/fallow, NH+4‐N/rye, and vetch‐N/vetch; mean 3‐yr cumulative NO−3 leaching losses were 6.11, 4.85, 0.35, and 2.51 g N m−2, respectively. Total recovery of added 15N in leachate was −3 derived from labeled N sources was generally −3, and quantity of NO−3 leached varied with year and time of year; differences in N‐source availability and mulch effects were sometimes indicated. Generally, cover crop effects were larger than N‐source effects. The NH+4 N source/rye cover system leached consistently less NO−3 than the vetch N source/vetch cover system, even though the fraction of water discharged was not consistently different.

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