Development of a deep irrigation method for rice encompassing water storage, aimed at increasing the environmental protection function of paddy fields. Growth and yield of rice in a year with a hot summer in the Tohoku region

摘要

A deep irrigation method is being developed to grow rice at a steady high yield in the Tohoku region of Japan, while increasing water storage, which is one of the functional benefits of paddy fields in environmental protection. The main method for promoting water storage function is to delay the runoff of river water, which is abundant due to snow melting and rainfall in the rainy season, until summer when there is often a shortage of water. To increase the water storage function of the paddy field, the water level is kept as high as possible using the present levee (maximum water depth 25-30 cm). The water level at the reproductive stage is kept at 25-30 cm to protect the plant from low temperatures. The water level is increased continuously until mid-July when water is abundant, assuming the water supply is steady, and the depth is controlled to have only one peak. The yield is increased using the deep irrigation method. Since this method was developed to cope with cool summers, yield may be lower in years with hot summers, when the yield under conventional cultivation is high. In 1994, there was a very hot summer, and the rice yield in the Tohoku region was high. Yields under the water storage, deep irrigation method were not inferior to those under conventional cultivation.