A NONLINEAR MODEL FOR CROP DEVELOPMENT AS A FUNCTION OF TEMPERATURE

The Beta function, commonly used as a skewed probability density funct ion in statistics, was introduced to describe the effect of temperatur e on the rate of crop development. The framework is set by three cardi nal temperatures, namely the base (T-b), the optimum (T-o) and the cei ling (T-c) temperature, The model parameters T-b and T-c and three oth er coefficients mu, alpha and beta can be used to derive;the value of T-o and the maximum development rate, Parameter alpha also characteriz es the curvature of the relationship with temperatures between T-b and T-o, and parameter beta describes the curvature between T-o and T-c. The model has one parameter less than the Rice Clock Model (RCM); and in contrast to the RCM, it ensures that the maximum-development rate o ccurs exactly at T-o. The model accurately described the response to t emperature of several developmental processes, and was superior to two widely used thermal time approaches in predicting rice flowering time .