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Nitrogen Rates and Mepiquat Chloride Effects on Cotton Lint Yield and Quality

M.W. Ebelhar, R.A. Welch, W.R. Meredith, Jr.


Interest in increased nitrogen (N) rates in combination with plant growth regulators continues in the Mississippi Delta and has been proposed to enhance cotton productivity. A 5-year study was initiated in 1992 to investigate the interaction of N rates (90, 120, 150, and 180 lb N/A) and mepiquat chloride (Pix) rates. Four Pix rates or systems have been incorporated including 1) an untreated control, 2) 2 oz/A applied four times (4X), 3) 4 oz/A applied 4X, and 4) a variable system dependent upon the growing conditions but sometimes using higher rates of Pix. A 15 to 25 lb seedcotton sample was harvested and processed through a commercial gin sequence including dual lint cleaners. Fiber samples were analyzed with HVI, as well as stelometer and arealometer measurements. Lint yields and HVI data have been summarized over a 4-year period. A combined analysis of lint yields showed a significant lint yield response to N rates up to 120 lb N/A with no additional response to either the 150 or 180 lb N/A rates. Applications of Pix did increase lint yields from 1001 to 1033 lb/A (an increase of 3.2%) over the 4-year period and across N rates. This increase was achieved with 2 oz Pix/A applied in four applications (total of 8 oz/A). In most years there was not a significant response to Pix although in some years there was a trend which lead to a significant response over the four years. Micronaire decreased with increasing N rates at both first and second harvest. Nitrogen had little effect on fiber length or strength, but did cause an increase in yellowness (Hunter's b). Pix application resulted in a slight increase (0.01 inches) in fiber length and varying effects on fiber strength. Pix applications did result in height reductions and shorter internodes (data not shown). Increasing N rates and using plant growth regulators to control growth would seem to be a solution for higher yields, however, the data does not suggest this option as the most realistic. Pix has been shown to hasten maturity in some cases while increasing N rates has been shown to delay maturity. Putting these two factors together usually results in no change in maturity. The final analysis must weigh the cost of the practice, including materials and application, against the realized benefit.

Reprinted from Proceedings of the 1996 Beltwide Cotton Conferences pp. 1373 - 1378
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998