NITROGEN AND MEPIQUAT CHLORIDE EFFECTS ON THE PRODUCTION OF NONRANK, IRRIGATED, SHORT-SEASON COTTON

Nitrogen fertility is an important component of irrigated, short-seaso n cotton (Gossypium hirsutum L.) production and is necessary to achiev e optimum yield. Excessive N, however, almost invariably results in de creased yield and quality of cotton lint and seed. Use of mepiquat chl oride (MC) (N,N,-dimethylpiperidinium chloride) for remediation of the detrimental effects of excessive N in cotton has been suggested. A fi eld experiment was conducted f or 3 yr to determine if MC applied at s elected rates on traditionally nonrank, irrigated, short-season cotton could influence cotton yield, related agronomic characteristics, and fiber properties at different N fertilizer rates. The experiment was c onducted near Altus, OK, on a Tillman-Hollister clay loam (fine, mixed , thermic Pachic Paleustoll). Cotton lint and seed yield responded pos itively to the Oklahoma State University recommended rate of 50 lb/acr e of fertilizer N in all 3 yr, but negatively at the higher rates in t he second and third years. Application of MC did not affect lint yield , seed yield, or lint/seed ratio in any year. Higher N fertilizer rate s generally produced taller plants (by as much as 3.2 in.) while MC si gnificantly reduced plant height (by as much as 5.7 in.) during this 3 yr. Percentage first harvest was increased (up to 5.50%) by MC in 1 y r, but was reduced (by as much as 17.40%) by higher N rates. Lint perc entages were generally reduced by N fertilizer in all years, but were not affected by MC in any year. Excessive N increased fiber grayness i n 1 yr and fiber yellowness in another, but did not affect micronaire, length, uniformity, strength, elongation, or leaf index in any of the 3 yr. Applications of MC increased fiber strength in 1 of 3 yr (by 3. 8%). They also affected elongation, fiber grayness, and leaf index in 1 yr a piece but not in the two others. Data from this study indicate that for measured parameters, the only consistent positive effects of MC use under any N fertilization regime was reduced plant height. No s ignificant N x MC rate interactions were noted.