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Title:   Author  item
                                            Sainju, Upendraitem
                                            SINGH, BHARAT - FORT VALLEY STATE UNIVERSitem
                                            WHITEHEAD, WAYNE - FORT VALLEY STATE UNIVERSitem
                                            WANG, SHIRLEY - FORT VALLEY STATE UNIVERS
  Submitted to: Agronomy Journal
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/28/2006
                                    Publication  Date: 4/4/2007
                                    Citation: Sainju, U.M., Singh, B.P., Whitehead, W.F., Wang, S. 2007. Accumulation and crop uptake of soil mineral nitrogen as influemced by tillage, cover crops, and nitrogen fertilization. Agronomy Journal. 99:682-691.Interpretive Summary: Intensive tillage and excessive N fertilization can increase N leaching in the groundwater, which is a major environmental concern. Tillage accelerates mineralization of crop residue and soil organic N and increases accumulation of NO3-N in the soil profile. Deep accumulation of NO3-N in the soil profile increases potential for N leaching in the shallow water tables. Similarly, N fertilization rates that exceed crop requirement can increase NO3-N accumulation in the soil profile and N leaching. Nitrogen recovery by crops seldom exceeds 70% of applied N and averages 50% or lower. Therefore, sustainable soil and crop management practices that optimize soil N availability and crop uptake are needed to reduce NO3-N accumulation in the soil profile and leaching.

The effects of three tillage practices [no-till, strip till, and chisel till], four cover crops [legume (hairy vetch), nonlegume (rye), 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) was examined on soil NH4-N and NO3-N movements at 0- to 120-cm depth and N uptake by cotton and sorghum. Nitrogen was harvested in cotton lint and sorghum grain but was returned from their biomass (stems + leaves) and that from cover crops to a Dothan sandy loam soil from 2000 to 2002 in central Georgia. Soil NH4-N and NO3-N contents were measured in April immediately after cover crop kill and in November after cotton and sorghum harvest, while cotton and sorghum N uptake was measured in November at the time of harvest.

 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 from Apr. 2000 to Nov. 2002. The increase with vetch was greater at 60- to 120- than at 0- to 60-cm. 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 to 65 than with 120 to 130 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 content, hairy vetch may increase soil N availability and cotton and sorghum N uptake but also increases the potential for N leaching due to greater soil N accumulation below the root zone compared with other cover crops. The potential for N leaching can be reduced and cotton and sorghum N uptake can be optimized by mixing vetch with rye.
                                Technical Abstract: Soil and crop management practices may influence soil mineral N, crop N uptake, and N leaching. We evaluated the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secaele cereale L.)], vetch + rye biculture, 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 hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] from 2000 to 2002 in central GA. Nitrogen was harvested in cotton lint and sorghum grain but was returned from their residues (stems + leaves) and from cover crops to Dothan sandy loam (fine-loamy siliceous thermic Plinthic Paleudults). Nitrogen supplied by cover crops was higher in vetch and vetch + rye than in rye and weeds. Soil NH4-N content at 0 to 30 cm was higher at postharvest than at prior to planting of cotton and sorghum 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 lost from crop residue and soil at 0 to 120 cm was higher with vetch than with other cover crops, probably due to leaching. 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, hairy vetch increased soil mineral N and cotton and sorghum N uptake compared with rye but also increased the potential for N leaching, regardless of tillage and N fertilization. The potential for N leaching can be reduced and crop N uptake can be optimized by mixing vetch with rye.


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