A model to estimate the increase of leaf number on the main culm of the rice plant

We are building an early warning system for preventing the decrease in rice -yield by cool summer damage. To monitor the developmental stage of rice pl ants in the whole Tohoku area, we constructed a model for estimating the pl ant age in leaf number. In the model, the sum of effective cumulative air t emperature for 10-24 degreesC necessary to advance the leaf number on the m ain culm by one was defined as the Leaf emergence interval. The model predi cts the plant age from effective cumulative air temperature. The leaf emerg ence interval was assumed to be constant in Phase I (before the leaf age 9. 1), increase at a fixed rate in Phase II (between leaf age 9.1 and 11.1), a nd to be constant in Phase III (after leaf age 11.1). The parameters of the model were decided from the leaf-emergence interval of seven varieties amo ng twelve leading varieties of Tohoku District in 1997 and 1998 in Morioka, The model estimated the leaf age of the Il varieties excluding "Okiniiri" in Morioka in 1999 with the mean error of 0.25 leaf which corresponds to 1. 7 days. From the application of this model to the rice- growers' fields in Miyagi and Yamagata Pref., the adaptability of this model was validated. Ho wever, in the growth types with vigorous tillering, the prediction accuracy was low because the leaf emergence interval was influenced by the number o f tillers.