Improvement in Rice Grain Quality by Deep-flood Irrigation and its Underlying Mechanisms

The increased occurrence of chalky rice grains as a result of global warming is becoming a serious problem. The application of deep-flood irrigation (DFI) to a water depth of 18 cm from the active tillering stage to the maximum tillering stage suppresses the occurrence of chalky grains under both high and normal temperature conditions without decreasing yields. The mechanism by which DFI reduces chalky grains was analyzed relative to carbohydrate supply as carbohydrate deficiencies have been proposed as a cause of chalky grains. DFI suppresses the occurrence of chalky grains due to the increased supply of carbohydrates to the panicles. In paddy fields where a water depth of 18 cm is not possible, such as in paddy fields with low levees or low water supplies, the combined use of moderate DFI at a water depth of 10 cm with deep planting can be substituted to produce high-quality rice. DFI did not damage root activity at the ripening stage, even in soils with a low redox potential. Although the DFI treatment slightly decreased the penetration resistance of the soil, the bearing capacity was not affected at the time of combine harvest.