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Title: Cotton nitrogen management in a high-residue conservation system: Cover crop fertilization

item Reeves, Donald
item Torbert, Henry - Allen

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2008
Publication Date: 8/1/2008
Citation: Reiter, M.S., Reeves, D.W., Burmester, .H., Torbert III, H.A. 2008. Cotton nitrogen management in a high-residue conservation system: Cover crop fertilization. Soil Science Society of America Journal. 72:1321-1329.

Interpretive Summary: High-residue cereal cover crops can add valuable organic matter to soil and reduce erosion, but may negatively affect nitrogen fertilizer efficiency of cash crops like cotton. We evaluated nitrogen fertilizer combinations applied to both a rye cover crop and following no-till cotton on a silt loam soil in northern Alabama. Applying 60 lbs nitrogen/acre to the rye cover crop and 40 lbs nitrogen/acre to cotton provided the most residue for soil protection and maximum cotton yields. Not fertilizing the rye cover and applying 80 lbs nitrogen/acre to cotton provided similar yields but insufficient residue to protect the soil from erosion. Fertilizing both the rye cover crop and cotton would cost $5.60/acre more than fertilizing cotton alone. However, fertilizing both the cover crop and cotton would reduce the risks of soil erosion, more rapidly increase soil organic matter on these degraded soils, and also reduce the potential for nitrogen losses to the environment. Farmers, extension agents, environmental groups, and fertilizer industries can use this information to more effectively reduce soil erosion and increase soil productivity, while maintaining economic cotton yield levels.

Technical Abstract: Nitrogen fertilization of cereal cover crops in conservation tillage cotton can increase biomass for soil coverage but may complicate cotton (Gossypium hirsutum L.)N recommendations. We conducted a 3-year field study on a historically tilled Emory silt loam (fine-silty, siliceous, active, thermic Fluventic Humic Dystrudepts) in northern AL to determine if N rates must be increased in high-residue conservation systems for cotton and to determine the effect of N applied to a rye (Secale cereale L.) cover crop on cotton N requirement. A strip plot design with 4 replications was used; horizontal treatments were rye N rates of 0, 34, and 67 kg N ha-1 and vertical treatments were cotton N rates of 0, 45, 90, and 135 kg N ha-1. Data collected included rye biomass, rye C:N ratios, cotton leaf N at first flower, lint yield, and lint quality. Labelled 15N (2.0 atom %) microplots were established in cover crop N plots with 34 kg N ha-1 and in cotton plots fertilized with 90 kg N ha-1; plant and soil samples were analyzed for 15N each year. Applications of 67 kg N ha-1 to rye and 45 kg N ha-1 to cotton provided optimal lint yield (1141 kg lint ha-1). Unfertilized rye with 90 kg N ha-1 applied to cotton provided similar yield (1120 kg lint ha-1), but rye biomass was lower (5310 kg residue ha-1 vs. 2906 kg residue ha-1, respectively).15Nitrogen analysis indicated immobilization of fertilizer N in this high-residue conservation tillage system, but sufficient N was mineralized to meet cotton needs. We recommend applying 67 kg N ha-1 to rye and 45 kg N ha-1 to cotton to obtain maximum rye residue for soil protection, good quality cotton lint, and maximum yields in high-residue conservation tilled cotton on silt loam soils.