NITROGEN ACCUMULATION IN COTTON GROWN CONTINUOUSLY OR IN ROTATION WITH PEANUT USING SUBSURFACE MICROIRRIGATION AND GOSSYM COMAX MANAGEMENT/

Excessive N application to cotton (Gossypium hirsutum L.) is an unnece ssary cost and a potential cause of elevated groundwater N. The object ives of this study were to determine if seed yields or excess N were a ffected by timing of N application via buried microirrigation tubing, tubing spacing, or peanut (Arachis hypogaea L.) rotation. The experime ntal design was a randomized complete block in split-plot arrangement with four replications. The main plots (continuous cotton and peanut-c otton rotation) were planted with cotton cultivar PD 3 in May of 1991 through 1994 on an Eunola loamy sand (fine-loamy, siliceous, thermic A quic Hapludult). Water and N were applied through microirrigation tubi ng that was buried 0.30 m directly under each row (IR) or under altern ate row middles (AM). Sidedress-N was applied in one 112-kg ha(-1) app lication (STD); five, 22-kg ha(-1) increments (INC); or 11- to 22-kg h a(-1) increments when required by GOSSYM/COMAX (GC) [a cotton growth m odel/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 i mprove 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-CC. It had 1.87 Mg ha(-1) yr(-1) seed yield, 8 kg ha(-1) yr(-1) excess N, 45 kg l ess 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.