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

Nitrogen fertility is an important component of irrigated, short-season cotton (Gossypium hirsutum L.) production and is necessary to achieve optimum yield. Excessive N, however, almost invariably results in decreased yield and quality of cotton lint and seed. Use of mepiquat chloride (MC) (N,N,-dimethylpiperidinium chloride) for remediation of the detrimental effects of excessive N in cotton has been suggested. A field experiment was conducted f or 3 yr to determine if MC applied at selected 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 conducted near Altus, OK, on a Tillman-Hollister clay loam (fine, mixed, thermic Pachic Paleustoll). Cotton lint and seed yield responded positively to the Oklahoma State University recommended rate of 50 lb/acre of fertilizer N in all 3 yr, but negatively at the higher rates in the second and third years. Application of MC did not affect lint yield, seed yield, or lint/seed ratio in any year. Higher N fertilizer rates generally produced taller plants (by as much as 3.2 in.) while MC significantly 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 yr, but was reduced (by as much as 17.40%) by higher N rates. Lint percentages were generally reduced by N fertilizer in all years, but were not affected by MC in any year. Excessive N increased fiber grayness in 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 significant N x MC rate interactions were noted.