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Title: Cotton nitrogen management in a high-residue conservation system: source, rate, method, and timing

Author
item REITER, M - UNIV OF ARK/AUBURN UNIV
item Reeves, Donald
item BURMESTER, C - AUBURN UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2008
Publication Date: 8/1/2008
Citation: Reiter, M.S., Reeves, D.W., Burmester, C.H. 2008. Cotton nitrogen management in a high-residue conservation system: source, rate, method, and timing. Soil Science Society of America Journal. 72:1330-1336.

Interpretive Summary: High-residue conservation tillage systems improve soil quality and reduce soil erosion, but may alter cotton nitrogen (N) management recommendations, which were developed from research with cotton grown in conventional tillage systems. A USDA-ARS scientist led a cooperative research project with scientists from the Alabama Agricultural Experiment Station, Auburn University, to evaluate nitrogen sources, rates, application methods, and timing for conservation-tilled cotton grown with a heavy rye cover crop on a silt loam soil in northern Alabama. The scientists found cotton nitrogen requirement was increased by 20-30 pounds of nitrogen per acre (lb N/acre) in conservation tillage systems with residue compared to conventional tillage systems. For producers wishing to have maximum cotton yields in the initial stages of high-residue cover crop farming systems, they recommended applying 160 lb N/acre in banded applications using urea-ammonium nitrate (UAN) at-planting. However, with nitrogen prices expected to rise above current averages of $0.46/lb-N for UAN and $0.56 lb-N for ammonium nitrate, this could cost growers up to $74/acre. Alternatively, if N efficiency and optimum return of lint per unit (lb) of applied N is the main goal, they recommended applying 110 lb N/acre as ammonium nitrate in broadcast applications split between at-planting and first match head square, at a cost of $62/acre. This information can be used by farmers, USDA-NRCS specialists, extension agents, environmental groups, and fertilizer industries to promote economically and environmentally efficient nitrogen applications on the 1.3 million acres of conservation tillage cotton grown in the Southeast.

Technical Abstract: Over 70% of the 94,226 ha of cotton (Gossypium hirsutum L.) in the Tennessee Valley of northern Alabama, USA, is produced using conservation tillage systems with cereal cover crops. Decreased N efficiency, as a result of N immobilization and/or ammonia volatilization in high-residue systems, requires development of new N fertilizer recommendations. We conducted a replicated 3-year field study (2000-2002) on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudult) to determine effects of N source [ammonium nitrate (AN) and urea-ammonium nitrate 32% (UAN)], N rates (0, 45, 90, 135, and 180 kg N ha-1), N application timing (all at-planting and 50-50 split between at-planting and first match head square), and N application method (banded or broadcast) on cotton grown in a high-residue rye (Secale cereale L.) conservation system. We evaluated lint yield, lint quality, leaf blade N, chlorophyll meter readings, petiole nitrate, rye biomass, and rye C:N ratios. Generally, 25 to 40% (22 to 36 kg N ha-1) more N was needed to reach optimal yields if N was split applied while N applied at-planting had yield responses with twice as much N as the recommended rate (90 kg N ha-1) in linear responses. Urea-ammonium nitrate applications resulted in greater yields when banded at-planting (1045 kg lint ha-1), while AN was more effective when broadcast applied at-planting or in split applications (1002 and 996 kg lint ha-1, respectively). Neither chlorophyll meter readings, petiole nitrate, nor leaf N were useful in prediction of cotton N deficiency. The most efficient (highest lint yield and plant N status measurement responses per kg of applied N) practice for cotton grown in high-residue conservation systems on these soils is to apply 40% more (126 kg N ha-1 total) N as a broadcast split application using AN. Over time we speculate that N requirements may be decreased as C and N pools reach a new equilibrium.