ABSTRACT

US Cotton growers are adopting COTMAN, a COTton MANagement system developed at the University of Arkansas and used to monitor crop development and aid in making end-of-season decisions. Currently, research-based decision guides have been developed to aid in identifying the last effective boll population and determining dates for safe termination of insect control and the application of defoliants based on physiological cutout, or NAWF=5. An area of cotton production that may benefit from COTMAN is the decision of when to stop irrigating the crop. The objective of this research was to investigate a crop-based recommendation for timing the final irrigation on cotton. Ten irrigation studies were conducted in four states (Missouri, Arkansas, Louisiana and Texas) during the 2003 growing season to investigate the response to late-season irrigation. Irrigation treatments consisted of different irrigation termination times at each site, with the first termination treatment targeted for approximately NAWF=5. The Texas studies dealt with drip and LEPA irrigation and are reported elsewhere. The study in Portageville, Missouri could not be completed due to late-season rains and herbicide drift seriously damaged the study at St. Joseph, Louisiana. In addition, data from one of the Arkansas studies were not available at the time of this writing. Only one of the five other mid-South studies showed significant differences in cotton yield with later irrigation. In the case where yield differences were significant in southeast Arkansas, yield tended to increase throughout the study period. No differences in fiber quality were observed; however, the samples were from studies where yield was not significantly affected. Additional studies will be required to develop a reliable recommendation for timing the final irrigation.