Estimating a initial stage of panicle formation and a heading date of rice plants by using the developmental index.

Abstract

The model for estimating a developmental stage of rice plant using the DeVelopmental Index (DVI) was introduced by Hone et al. (1986). We conducted further research to clarify the function form of DeVelopmental Rate (DVR) to be applied to wide range of rice cultivating area in Japan. The objects of this study are to compare the functions of DVR obtained in Tsukuba and to apply this model to some local data sets.Four rice cultivars were transplanted in Tsukuba three to four times a year in 1985 and 1986. The parameters of DVR functions were determined by the least squares method. Various DVR functions obtained in Tsukuba were applied to local data sets in Aomori and Miyazaki.The standard errors of functions of both air temperature and a day length were smaller than that of air temperature alone. This tendency was significant for the cultivar, Mizuho. Under our experimental conditions, the DVR did not show a big difference between the linear functions and the nonlinear ones.In local data sets, the longest and the shortest days from the transplanting to a certain stage were predicted. The modified model which has parameters determined from the Tsukuba data sets was more effective in prediction than the local model. Since the Tsukuba data included the one from several different cropping seasons, it must have worked efficiently to the excluded data.