A Model for Evaluating Climatic Productivity and Water Balance of Irrigated Rice and Its Application to Southeast Asia(<Special Issue>Commemorative Issue on the Retirement of Professor Tadayo Watabe : Rice and Rice Culture in Tropical Asia)

Abstract

A physiology-oriented dynamic model incorporating crop physiological data on IR36 rice was proposed for the evaluation of climatic productivity and water balance of irrigated rice. The model explained well the location-to-location variations of actual rice yield in Japan and the U. S. A. The climatic productivity per crop at Bangkok (Thailand) and Los Banos (Philippines) was evaluated to be approximately 9.0 and 11.0 ton/ha for the wet- and dry-season crops, respectively. These values were significantly lower than the 19.3, 15.6 and 13.9 ton/ha evaluated for California, Milano and Niigata, respectively. The lower productivity in tropical Southeast Asia is mainly attributable to the too rapid development of the crop due to the higher temperature. Since three to four crops per year are possible in tropical monsoon regions, the annual climatic productivity in tropical monsoon Asia was estimated to be at least twice as high as in the most temperate regions. The climatic water balance at Bangkok and Los Banos was evaluated to be about -460mm per dry-season crop, implying that at least this amount of irrigation water is necessary for the dry-season rice crop there.