1990 Volume 59 Issue 4 Pages 687-695
Rice developmental stage is quantified by a continuous variable termed developmental index, DVI, of which value at the emergence is detined to be 0 and at the heading to be 1.0. The value of DVI at any moment between these two boundary stages can be given by integrating the developmental rate, DVR, with respect to time, in a similar way as de Wit et al. (1970) applied. We propose the following equation for DVR of rice as a function of daily mean temperature T and day length L, [numerical formula] where G is a minimum number of days required for heading of a given cultivar; Th is the temperature at which DVR is the half of the maximum under a given day length; Lc is the critical day length for development; DVI* is the value of DVI at which the crop becomes sensitive to photoperiod; A and B are the parameters. By utilizing the Simplex method, a least square regression method for non-linear functions, the values of these parameters can be estimated from experimental data sets on rice phenology and the environments obtained under field conditions. The model explained heading dates of Nipponbare rice grown under 35 different conditions with S.E.= 3.6 days, while the traditional effective degree day model explained the same data with S.E.= 6.5 days.
