COMPARISON OF METHODS FOR ESTIMATING PLASTOCHRON IN COTTON PLANT UNDER TROPICAL WEATHER CONDITIONS

The time for growth and development of plants is influenced by air temperature and other environmental variables. This research was based on three methods for calculating plastochron timing of cotton plant under tropical weather conditions, using thermal units accumulation as variable, calculated from the average daily air temperature, considering the concepts of degrees-day and accumulated thermal time. Two methods for calculating average daily temperature and three methods for obtaining Degrees-Day values and accumulated thermal time were used. Whereas the accumulated thermal time is a method that considers that the growth and development of plants have linear response to the air temperature influence, it was also tested a non-linear approach, as described by Wang & Engel (1998), called, in this study, beta function. For the beta function, average daytime temperatures were also used, obtained by the two different calculation methods. The beta function was the best option for estimating plastochron and the method for calculating the Average Daily Temperature influenced the results. KEY-WORDS: Gossypium hirsutum; degrees-day; beta function; physiological age; thermal units.