ABSTRACT

US Cotton growers are adopting COTMAN, a COTton MANagement system developed at the University of Arkansas, 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. Eleven irrigation studies were conducted in five states (Missouri, Arkansas, Mississippi, Louisiana and Texas) during the 2002 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 study dealt with drip irrigation and is reported elsewhere. Of the others, only five of the ten studies could be completed due to rain and only one of the five showed significant differences in cotton yield with later irrigation. In central-east Arkansas no significant yield differences were observed later than 16 days or 343 DD60 after NAWF=5. Only one of the studies (northeast Louisiana) was harvested twice, and while there was a trend for lower percent first harvest associated with later irrigation, the differences were not significant. Additional studies will be required to develop a meaningful recommendation.