Nitrogen storage with cover crops and nitrogen fertilization in tilled and nontilled soils
Improved crop and N management practices are needed to increase soil N storage so that N fertilization rate and the potential for N leaching can be reduced in tilled and nontilled soils. We examined the influence of cover crops and N fertilization rates on N inputs from cover crops, cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] and soil total N (STN) content at the 0- to 120-cm depth in no-tilled, strip-tilled, and chisel-tilled Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) from 2000 to 2002 in central Georgia. Cover crops were legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch + rye), and winter weeds and N fertilization rates were 0, 60 to 65, and 120 to 130 kg N ha–1. Nitrogen inputs in above- and belowground plant biomass varied with the season and were greater in vetch and vetch + rye with N rates than in rye and weeds with or without N in tilled and nontilled soils. The STN concentration varied with sampling times and decreased with depth. The STN content at 0 to 90 cm was greater in vetch and vetch + rye with N rates than in weeds with or without N in no-tilled and chisel-tilled soils. Similarly, STN content at 0 to 30 cm was greater with vetch and vetch + rye than with weeds in strip-tilled soil. As a result, N storage at 0 to 30 cm gained at 71 to 108 kg N ha–1 yr–1 in vetch and vetch + rye with N fertilization compared with a loss at 110 kg N ha–1 yr–1 to a gain at 40 kg N ha–1 yr–1 in weeds with or without N fertilization in no-tilled and chisel-tilled soils. In strip-tilled soil, N storage gained at 101 to 103 kg N ha–1 yr–1 with vetch and vetch + rye compared with a loss at 91 kg N ha–1 yr–1 with weeds. Nitrogen storage in tilled and nontilled soils can be increased by using legume or a biculture of legume and nonlegume cover crops compared with no cover crop with or without N fertilization. Because of similar levels of soil N storage and cotton and sorghum N uptake, legume can be replaced by biculture cover crop and N fertilization rate can be reduced to reduce the cost of N fertilization and the potential for N leaching.