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Title: MANAGING NITROGEN FOR COTTON IN A HIGH-RESIDUE CONSERVATION TILLAGE SYSTEM

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

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/7/2003
Publication Date: 5/12/2003
Citation: Reiter, M.S., Reeves, D.W., Burmester, C.H. 2003. Managing nitrogen for cotton in a high-residue conservation tillage system. National Cotton Council Beltwide Cotton Conference.

Interpretive Summary: High-residue producing small grain cover crops are becoming a common management practice for cotton grown in the Tennessee Valley region. Nitrogen fertilizer efficiency is altered by residue in conservation systems and new nitrogen management recommendations may be needed for cotton produced 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. We found that cotton grown in such systems may initially require up to 30 lb more nitrogen/acre compared to conventional systems. However, nitrogen requirements may not be as high for systems with less residue and may be reduced over time. 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. Using 120 lb N/A, at a cost of $0.19/lb nitrogen for UAN ($22.80/A) and $0.28/lb nitrogen for AN ($33.60/A), producers can save $10.80/acre by using UAN rather than AN. Banding all UAN at planting may help producers maximize cotton yield and profit in high-residue conservation systems. This information can be used by extension, NRCS, and producers to improve nitrogen efficiency in conservation production systems that sustain soil quality.

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. Results suggest that 120 lb N/A may be needed to optimize yields (781 lb lint/A in 2000, 1026 lb lint/A in 2001, and 875 lb lint/A in 2002). Generally, highest yields were obtained when N was applied at-planting (803 lb lint/A in 2000, 957 lb lint/A in 2001, and 863 lb lint/A in 2002). 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.