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Title: NITROGEN MANAGEMENT FOR COTTON GROWN IN A HIGH-RESIDUE COVER CROP CONSERVATION TILLAGE SYSTEM

Author
item REITER, M - AUBURN UNIVERSITY
item Reeves, Donald
item BURMESTER, C - AUBURN UNIVERSITY

Submitted to: Southern Conservation Tillage for Sustainable Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/24/2002
Publication Date: 6/24/2002
Citation: Reiter, M.S., Reeves, D.W., Burmester, C.H. 2002. Nitrogen management for cotton grown in a high-residue cover crop conservation tillage system. In: Van Santen, E., editor. Proceedings of the 25th Annual Southern Conservation Tillage Conference for Sustainable Agriculture - Making Conservation tillage Conventional: Building a Future on 25 Years of Research. Special Report no. 1, Alabama Agricultural Experiment Station and Auburn University, June 24-26, Auburn, Alabama. p. 136-141.

Interpretive Summary: High-residue conservation tillage systems improve soil quality but may alter nitrogen management recommendations for cotton grown in these systems. We evaluated 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. Preliminary results suggest that nitrogen requirement of cotton in such systems is increased by 30 lb nitrogen/A compared to conventional systems. Ammonium nitrate applications resulted in greater yields when broadcast at planting while urea-ammonium nitrate (UAN) applications resulted in greater yields when banded, regardless of application timing. At current prices for ammonium nitrate and UAN, the preliminary data suggest the most efficient and economical practice for cotton grown in high-residue conservation systems would be to apply 120 lb N/A as UAN in a banded application at planting. Using 120 lb N/A, at a cost of $0.19/lb N for UAN ($22.80/A) and $0.28/lb N for AN ($33.60/A), producers can save $10.80/A by using UAN rather than AN. Applying all N at planting saves trips across the field, reducing operating costs and compaction. Banding all UAN at planting may help producers maximize cotton yield and profit in high-residue conservation systems.

Technical Abstract: Over 70% of the cotton (Gossypium hirsutum L.) in the Tennessee Valley of northern Alabama is currently raised using conservation tillage techniques. High-residue small grain cover crops are becoming a common tool in these systems, but N immobilization may occur causing previous N recommendations to be obsolete. A replicated 3-year field study was initiated in 1999 in the Tennessee Valley of Alabama on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult) to test a factorial arrangement of N source (ammonium nitrate and urea-ammonium nitrate), N rates (0, 40, 80, 120, 160 lb N/A), N application timing (all at planting and 50-50 split between at planting and first square), and N application method (banded or broadcast) for cotton grown in a high-residue rye (Secale cereale L.) conservation system. Preliminary results suggest that 120 lb N/A may be needed to optimize yields (781 lb lint/A in 2000 and 1026 lb lint/A in 2001). Generally, highest yields were obtained when N was applied at planting (803 lb lint/A in 2000 and 957 lb lint/A in 2001). Ammonium nitrate applications resulted in greater yields when broadcast at planting while UAN applications resulted in greater yields when banded, regardless of application timing. At current prices for AN and UAN, the preliminary data suggest the most efficient and economical practice for cotton grown in high-residue conservation systems would be to apply 120 lb N/A as UAN in a banded application at planting.