Heat Units and Earliness in Upland Cotton

Warner D. Fisher


 
ABSTRACT

For the past several years at the Cotton Research Center, the earliness or maturity distribution of the crop has been determined by hand harvesting selected plots at two-week intervals starting about 1 September. The percent of the total crop harvested on 1 September has varied from 5.3% to 65.3% (Table 1). This variation has occurred even though planting dates and total yields have been very consistent over the years. The one observation that we made was that the years with cold springs resulted in later maturity as contrasted to those years with warmer spring weather. This observation led us to the consideration of heat units to tr to identify more precisely the effects of temperature on earliness.

The heat units used in this study were based on weather bureau temperatures measured at Phoenix Sky Harbor Airport approximately five miles distant. We simply used the maximum daily temperature (86OF limit) plus the minimum temperature divided by two minus 55.

A very high correlation was found between percent open on 1 September and the number of heat units accumulated from the day of planting through April 30. Figure 1 shows a correlation coefficient of .92 and a regression equation of Y = -27.0245 + .1215 X, where Y is the estimated percent open on 1 September and X is the number of heat units from planting date through 30 April. The variety used in these measurements was Deltapine 61. Heat units accumulated during May showed a very low, non-significant correlation with earliness. Perhaps this is explained by the fact that May temperatures in the Phoenix area are generally sufficiently high to give near maximum rate of plant development. April temperatures, however, show a great deal more variation from year to year.



Reprinted from 1985 Proceedings: Beltwide Cotton Production Research Conferences pg. 364
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998