Nitrate Leaching as Influenced by Cover Cropping and Nitrogen Source
McCracken, Daniel V. | Smith, M Scott | Grove, John H. | Blevins, Robert L. | MacKown, Charles T.
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 <5% for all treatments, and the percentage of leached NO⁻₃ derived from labeled N sources was generally <15%. In the winter-fallow lysimeters, effects of N source on the fraction of water input discharged, concentration of NO⁻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. Contribution no. 93-3-82 of the Kentucky Agric. Exp. Stn.
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