Saturday, 15 July 2006

Soil and Crop Nitrogen as Influenced by Tillage, Cover Crops, and Nitrogen Fertilization.

Upendra Sainju1, Bharat Singh2, Wayne Whitehead2, and Shirley Wang2. (1) USDA-ARS-NPARL, 1500 N Central Ave., Sidney, MT 59270, (2) Fort Valley State Univ, 1005 State University Drive, Fort Valley, GA 31030

Soil and crop management practices may influence soil mineral N, crop uptake, and N leaching. We evaluated the effects of three tillage practices [no-till, strip till, and chisel till], four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of vetch and rye, and winter weeds or no cover crop}, and three N fertilization rates (0, 60 to 65, and 120 to 130 kg N ha-1) on soil NH4-N and NO3-N contents at the 0 to 120 cm depth and N uptake by cotton (Gossypium hitsutum L.) and sorghum [Sorghum bicolor (L.) Moench]. Nitrogen was harvested in cotton lint and sorghum grain but was returned from their biomass (stems + leaves) and that from cover crops to Dothan sandy loam (fine-loamy siliceous thermic Plinthic Paleudults) from 2000 to 2002 in central GA. Soil NH4-N content increased with increasing N rate and was higher at postharvest than at preplanting of cotton and sorghum. Soil NO3-N also increased with increasing N rate and was higher with vetch than with rye or weeds at 60 to 120 than at 0 to 60 cm from Apr. 2000 to Nov. 2002. In no-till and chisel till, NO3-N at 0 to 10 and 10 to 30 cm was also higher with vetch than with rye and weeds in April 2000 and 2002. Nitrogen uptake 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 uptake by sorghum grain and cotton and sorghum biomass were greater with vetch than with rye and greater with 120 to 130 than with 0 kg N ha-1. Because of higher N supply, hairy vetch may increase soil mineral N and crop uptake compared with rye but also increases 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.

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