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

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 occurr 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, 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. [ABSTRACT FROM AUTHOR]
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