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 for 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 5.5%) by MC in 1 yr, but was reduced (by as much as 17.4%) 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 apiece 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 × MC rate interactions were noted. Research Question Nitrogen fertility is an important component of irrigated short‐season cotton production and is necessary to achieve optimum yield. Excessive N, however, often results in maturity delays and subsequent decreased yield and quality of fiber and seed. Use of mepiquat chloride (MC) has been suggested to counteract the detrimental effects of excessive N in cotton. The objective of this study was to determine whether 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. Literature Summary Mepiquat chloride has been used in full‐season, picker‐type cotton production systems with varied success. Application of MC is reported to consistently decrease plant size. Some authors report significant yield increases under certain circumstances; others little or none. Few studies have been published pertaining to irrigated, short‐season cotton as produced on the Rolling Plains of Oklahoma and Texas and to the potential of MC to alleviate detrimental effects of excessive N in that region. Study Description A field experiment was conducted on a Tillman‐Hollister clay loam, near Altus, OK, for 3 yr. The experiment was a randomized complete block design with a factorial arrangement of treatments and four replications. Nitrogen rates of 0, 50, 100, and 200 lb of actual N/acre were applied broadcast preplant and disk incorporated. ‘Paymaster 404’ cotton was seeded each year at 21 lb/acre. Mepiquat chloride rates of 0, 0.022, and 0.044 lb a.i./acre (½ pint and 1 pint/acre of 0.35 lb/gallon material, respectively) were superimposed on N rates and foliar applied at early bloom. Irrigation and insecticides were applied as judged necessary. Applied Questions What are the effects of excessive N in nonrank, irrigated, short‐season cotton production? Cotton lint yield responded positively to 50 lb/acre of fertilizer N in all 3 yr. Excessive accumulation of N at the two higher rates, however, resulted in lint yield reductions by the second and third years of the experiment (Fig. ). Seed yield response followed the same pattern as did lint yield, though seed weight increased faster than lint weight. Plant height increased up to 3.2 in. by N fertilization in these experiments while maturity (as measured by percentage first harvest) declined by as much as 17.4%. Lint percentages declined, thus increasing harvest and ginning costs per bale. Higher N rates 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. Use of N displayed positive and negative effects. At the modest rate of 50 lb/acre, application of N appears economically justified because of the increased lint and seed yield; whereas, the higher rates do not because of the suppressed yields in years 2 and 3. Excessive N resulted in various other unfavorable effects on the plant, higher costs of production, and the potential for environmental degradation. Oklahoma State University soil test recommendations for N fertilizer management were appropriate for maximizing lint yields over the 3 yr. Could any effects of excessive N be overcome in this production situation with the growth regulator mepiquat chloride? Mepiquat chloride did not influence lint and seed yield or their ratio in any of the 3 yr in this experiment. Applications of MC consistently reduced plant height in all years by as much as 5.7 in. However, since this cotton was not rank initially and since plant height correlated poorly with stripper lint percentage, the reductions in height were of doubtful direct economic value. Use of MC increased earliness by up to 5.5% in 1 yr, but was ineffective in another. Fiber strength was increased by up to 3.8% in 1 yr, but not in the 2 other yr. Fiber elongation was increased (a favorable effect) as was grayness (an unfavorable effect) in 1 yr, but in another year leaf index was increased (an unfavorable effect). Rates of MC did not significantly influence micronaire, length, uniformity, or yellowness. Results from this study conducted on nonrank, irrigated, short‐season cotton indicate that, with the exception of plant height, MC application to any N fertilizer management regime had minimal direct benefit on measured parameters. Effect of N fertilization on lint yield in southwest Oklahoma over a 3‐yr period, in actual units.