Effect of irrigation termination on the yield, earliness, and fiber qualities of cotton

Irrigation of cotton (Gossypium hirsutum L,) in the humid regions of the U. S. Cotton Belt is one of the least understood crop management practices. Ir rigation problems are compounded by fall weather that necessitates crop ter mination and harvest regardless of stage of development to avoid extended p eriods of inclement weather. The objective of this research was to determin e the optimum time to end irrigation for cotton grown in the Arkansas Delta . Five cotton cultivars (Stoneville 453, Stoneville 506, Deltapine 20, Delt apine 51, and Deltapine 90), two ethephon ((2-chloroethyl)phosphonic acid) applications (0 and 2.0 lb/acre), and three dates of irrigation termination (1 August, 15 August and 31 August) were tested at the University of Arkan sas Southeast Branch Experiment Station (SEBES) from 1990 to 1993. Signific ant differences in yield, earliness end fiber properties were found as a re sult of irrigation termination, cultivar, and ethephon treatment. Yield was maximized by terminating irrigation on 15 August. The greatest yielding cu ltivars were generally Stoneville 493, Deltapine 51, and Deltapine 20, Delt apine 90 was usually the lowest yielding. Ethephon treatments did not signi ficantly affect yield. Earliness, as estimated by the fraction of Lint coll ected in the first harvest (PFH) and the fraction of open bells, was reduce d by later irrigations. DPL 90 was the latest maturing cultivar with minima l differences among the other four cultivars. Ethephon treatments and ethep hon x cultivar interactions were found to significantly influence PFH in se ven of 12 irrigation treatment-years, Ethephon applications increased PFH. Fiber properties were inconsistently affected by irrigation, and unaffected by ethephon applications. DPL 90 had the strongest fiber, but few other me aningful differences in fiber properties of the cultivars were observed.