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Agronomic Factors and Yield Variability

William R. Meredith, Jr.


A review of some agronomic factors that influence yield is given. Yield is determined through the effects of its yield components: number of bolls/acre, average boll weight, and lint percentage. The 1995 yields in Mississippi were about 80% of their 15-year average. In one comparative study, number of bolls was less than in 1994 by 35% and boll size was about 65% lower than in 1994. Excessive use of Nitrogen (N) on strong land may be one cause of yield instability in the Mississippi Delta. Excessive N rates result in greater vegetative development, delayed maturity and reduced income. The use of Mepiquat Chloride (MC) as a growth regulator has resulted in both positive and negative yield responses. MC reduces the plant height and vegetative growth. Positive response to MC occurs mostly on strong land, when high rates of N and irrigation are used. The optimum planting date in the Mississippi Delta falls between April 20 and May 10. Plantings earlier than April 20 frequently result in poor stands. Plantings later than May 10 generally result in reduced yields and increased vulnerability to insects and bad weather. When crop terminators are applied to bolls 36 days old or younger, or that have less than 600 DD60s of development, both the boll weight and the micronaire are reduced. This review emphasizes that the management decisions in the use of these factors requires proper timing in their use and consideration of the plants' growth and development.

Reprinted from Proceedings of the 1996 Beltwide Cotton Conferences pp. 180 - 184
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998