Water management of paddy rice cultivation in Hokkaido


 Although Hokkaido is devoted to rice production, the crop in question is mainly cultivated in the Sorachi and Kamikawa regions, is the second largest next to Niigata. Of the overall rice crop in this area, its composition includes 40% “Nanatsuboshi” cultivar, 25% “Kirara397,” and 35% “Yumepirika.” Paddy field and upland rotation is carried out, but since converted upland soils are too fertile and spoil the flavor of the grains, rice produced in this type of paddy is mainly used for the production of heavily processed rice products. In very large fields, direct sowing is preferred to the raising and planting of seedlings.
 Since melted snow is available in addition to rain in Hokkaido, water resources are comparatively plentiful, and serious droughts are rare. Recently, there was a water shortage in 2003, causing the soil to drain poorly in many places at a rate of only 10 mm a day.
 Measures used to protect crops against low temperatures are important components of the water management technology in Hokkaido. The primary method is to utilize flooding to protect plants. While the water depth is about 60 mm during general deep water management, it is raised to about 200 mm in Hokkaido. Thus, paddies are built to have stronger levees, water drainage is controlled only by the outlet, and there is no system in place to allow for fine adjustment of the water level.
 The primary part of time series water management the use of two rounds of midseason drainage, during both the panicle formation stage and the heading stage. In low-temperature years, however, midseason drainage may be forgone, and root damage may be prevented by soil reduction. Drainage is carried out, considering the trade-offs of direct damage by low-temperature conditions. After the heading stage, the water level is kept slightly low, after which intermittent irrigation is performed. Water is drained about 25 days after heading. Because harvest is still about 25 days away, the paddies are irrigated when dry, to keep the paddy soil wet.