Abstract
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 plants in the whole Tohoku area, we constructed a model for estimating the plant age in leaf number. In the model, the sum of effective cumulative air temperature for l0-24°C necessary to advance the leaf number on the main culm by one was defined as the leaf emergence interval. The model predicts the plant age from effective cumulative air temperature. The leaf emergence interval was assumed w 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), and 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 among twelve leading varieties of Tohoku District in 1997 and 1998 in Morioka. The model estimated the leaf age of the 11 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. However, in the growth types with vigorous tillering, the prediction accuracy was low because the leaf emergence interval was influenced by the number of tillers.
