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Determining the Optimum Timing for the Final Irrigation on Mid-South Cotton

Earl Vories, Jeremy Greene, William Robertson, Tina Teague, Bobby Phipps and Steve Hague


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. Eight irrigation studies were conducted in three states (Missouri, Arkansas and Louisiana) during the 2001 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. Only two of the eight studies showed significant differences in cotton yield with later irrigation. In those two cases, the differences for southeast Arkansas were observed later in the growing season (after 20 days or 470 DD60 after NAWF=5) than for northeast Arkansas (no differences were observed later than 11 days or 220 DD60 after NAWF=5). Two of the studies were harvested twice and in both there was a significantly lower percent first harvest associated with later irrigation. Very little difference was observed in fiber quality for the different irrigation termination treatments. Additional studies will be required to understand differences observed between locations.





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Document last modified May 20, 2002