Abstract
Suppression of the occurrence of chalky grains caused by a high temperature at the ripening stage of rice is an urgent issue in rice production in Japan. Deep flood irrigation with a water depth of 18 cm is an effective measure to avoid the occurrence. However, the area of paddy fields that can keep this level of water depth is limited, because the plants are usually not so high. Here, we examined the effects of flood irrigation at a water depth of 10 cm and deep planting (depth of 6 cm), and their combination on the yield and quality of rice using cultivars Hatsuboshi and Koshihikari which are sensitive and moderately tolerant to a high temperature at the ripening stage, respectively. In Hatsuboshi, deep planting combined with 10-cm irrigation from the rooting stage to the maximum tillering stage reduced the occurrence of chalky grains without yield reduction that was caused by an 18 cm flood irrigation. In Koshihikari, 18-cm flood irrigation was the best to reduce chalky grains, but 10-cm flood irrigation also reduced chalky grains significantly without significant yield reduction. Deep flood irrigation (18 cm) decreased the redox potential of soil, but did not damage the root system at the ripening stage. In addition deep flood irrigation did not reduce soil-bearing capacity, and was not considered to prevent combine harvesting.
