Abstract
In Ohgata Village, paddy rice is grown under very low soil water condition after the panicle differentiation stage, because the residual water in the paddy field is drained to facilitate a combine harvesting. The water content of the rice plant and the stomatal aperture are expected to be reduced under these conditions, and it is also conjectured that the photosynthetic rate is reduced by the poor soil water supply resulting in reduced dry matter production. However, the yield in Ohgata is very high. In this study, we investigated the relationships between the stomatal aperture and crop growth rate (CGR), net assimilation rate (NAR), leaf area index (LAI) and dry matter production in Ohgata in comparison with those in nearby Gojome where paddy rice was cultivated by conventional water managementt. The stomatal aperture in Ohgata was smaller than that in Gojome. However, CGR in Ohgata was higher than that in Gojome. These results show that even on sunny days with high-intensity light, low humidity and high transpiration, the water content of the rice plant is maintained at a certain level by closing stomata to adapt to such ambient environments and photosynthetic rate is kept high through-out the day. From these results, we propose the outline of our rice cultivation theory.
