Assessment of resistance of rainfed lowland rice to aerobic condition in northeastern Thailand based on the dynamics of nutrients in soil

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The rainfed lowland is a major rice ecosystem in Thailand. In northeast Thailand, especially, rice plant experiences anaerobic, aerobic and drought conditions alternately during the life cycle and moreover soil capacity of nutrient supplies and retention is very low due to sandy soil. Therefore, rice yield is seriously reduced. Our objectives were to clarify the nutrient dynamics in soil and rice plants and to improve rice yield with improvement of nutrient absorption. As a result, phosphorus content in soil was not high and the deficiency was occurred. But, phosphorus fertilizer did not effective, because phosphorus is hardly moving in soil, and root growth was strongly reduced by anaerobic-aerobic transition, and the favorable nitrogen had to be accompanied. We could find out some lines showing relatively good growth under this rainfed condition. They are assumed to have the capacity to absorb phosphate effectively. It is necessary to be analyzed to improve rice productivity.