MICROIRRIGATION SCHEDULING AND TUBE PLACEMENT FOR COTTON IN THE SOUTHEASTERN COASTAL-PLAIN

Three irrigation scheduling methods and two microirrigation tube place ments were evaluated on three cotton (Gossypium hirsutum L.) cultivars for three years on a southeastern Coastal Plain soil. Irrigation sche duling methods included two computer models, GOSSYM/COMAX and PRISM, a nd a method using tensiometers. Microirrigation tubing was placed on t he soil surface, either adjacent to every row or in alternate furrows. Growing-season rainfall amounts ranged from 313 mm in 1990 to 544 mm in 1988. Rainfall distribution also varied widely within each year. In a similar manner, irrigation amount and frequency varied among schedu ling methods and years, but no method consistently required the larges t or smallest amount of irrigation. Cotton lint yields ranged from 850 to 1105 kg/ha over all years, but there were few significant differen ces among irrigation treatments within a year, even between the rainfa ll-only and irrigated treatments. Lint yields were significantly great er for the PD3 and DPL90 cultivars than for the Coker 315 cultivar dur ing the three-year period, and the PD3 cultivar had a greater yield re sponse to irrigation. The tensiometer-every row tube placement is the only irrigation treatment that produced cotton lint yields significant ly higher than the rainfall-only treatment each year. The tensiometer scheduling method also produced significantly greater yields each year . Although yield differences occurred, they were relatively small. Thi s fact, along with the inconsistent differences in the amount of irrig ation water required, suggests that the preferred method for a particu lar application will probably depend more upon water or labor requirem ents, cost, or personal preference. Also, there was no difference in y ield between the two tube placements. Because the alternate-furrow pla cement requires only half as much tubing, which will reduce installati on costs by about 30%, it appears to be the preferred placement for th is soil. Further research is needed to refine irrigation scheduling fo r cotton in this region.