Accumulation and Crop Uptake of Soil Mineral Nitrogen as Influenced by Tillage, Cover Crops, and Nitrogen Fertilization

Management practices may influence soil N levels due to crop uptake and leaching. We evaluated the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops [hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), vetch + rye biculture, and winter weeds or no cover crop], and three N fertilization rates (0, 60-65, and 120-130 kg N ha(-1)) on NH4-N and NO3-N contents in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Paleudults), and N uptake by cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] from 2000 to 2002 in central Georgia. Nitrogen content was higher in vetch and vetch + rye than in rye and weeds. Soil NH4-N content at 0 to 30 cm was higher at harvest than at planting, and higher in NT or vetch with 120 to 130 kg N ha(-1) than with other treatments. The NO3-N content at 0 to 120 cm varied with date of sampling and was higher with vetch than with rye and weeds. The NO3-N content at 0 to 10 cm was higher in CT with vetch than in NT and ST with rye or weeds. From November 2000 to April 2001 and from November 2001 to April 2002, N loss from crop residue and soil at 0 to 1120 cm was higher with vetch than with other cover crops. Nitrogen removed by cotton lint was higher with rye than with other cover crops in 2000 and higher with 0 and 60 than with 120 kg N ha(-1) in 2002, but N removed by sorghum grain and cotton and sorghum biomass were higher with vetch than with rye, and higher with 120 to 130 than with 0 kg N ha(-1). Because of higher N supply, vetch increased soil mineral N and cotton and sorghum N uptake compared with rye, but also increased the potential for N leaching. The potential for N leaching can be reduced and crop N uptake can be optimized by mixing vetch with rye.