Abstract
Excessive N application to cotton (Gossypium hirsutum L.) is an unnecessary cost and a potential cause of elevated groundwater N. The objectives of this study were to determine if seed yields or excess N were affected by timing of N application via buried microirrigation tubing, tubing spacing, or peanut (Arachis hypogaea L.) rotation. The experimental design was a randomized complete block in split-plot arrangement with four replications. The main plots (continuous cotton and peanut-cotton rotation) were planted with cotton cultivar PD 3 in May of 1991 through 1994 on an Eunola loamy sand (fine-loamy, siliceous, thermic Aquic Haphidult). Water and N were applied through microirrigation tubing that was buried 0.30 m directly under each row (IR) or under alternate row middles (AM). Sidedress-N was applied in one 112-kg ha−1 application (STD); five, 22-kg ha−1 increments (INC); or 11- to 22-kg ha−1 increments when required by GOSSYM/COMAX (GC) [a cotton growth model/expert system]. Rotation did not significantly affect any of the measured parameters. Cotton managed with the IR-STD treatment had the highest seed yield, 2.02 Mg ha−1 yr−1. The GC management did not improve seed yield, but it did reduce excess N (fertilizer N - seed N) to <20 kg ha−1 yr−1. The best overall treatment was AM-GC. It had 1.87 Mg ha−1 yr−1 seed yield, 8 kg ha−1 yr−1 excess N, 45 kg less N applied, and 50% less tubing installed. Cotton managed by AM-GC also had a low (9.2) ratio of accumulated shoot N per 100 kg of lint.
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