To cope with cold weather in the northern part of Japan, early-maturing varieties resistant to cold weather were developed. Rice growing in the cold district is characterized by the use of good quality older seedlings for early transplanting, deepwater irrigation to protect the crop from low night temperature, windbreak nets, and application of organic matter to improve soil fertility. Production constraints Irrigated fields act as a reservoir for rainwater and as catchments to protect steep slopes from flooding and soil erosion. Irrigated fields have the advantage of higher yield and continuous cropping compared with upland fields. Rice is occasionally damaged by drought, but the injury is not so serious in the irrigated fields.
Cold damage experienced in summer is serious in some years in northern Japan.
Usually, there is severe incidence of rice blast disease in cool summer weather. Heavy rainfall at the end of the rainy season causes local flooding. Rice is sometimes damaged by typhoons, especially in the southern regions. Early season culture has been established to avoid typhoons in the southwestern part of the country. Most ricefields are in the plains of the major river basins.