COMPARISON OF IRRIGATION REQUIREMENTS BETWEEN TRANSPLANTING CULTIVATION AND DIRECT-SEEDING CULTIVATION IN LARGE-SIZED PADDY FIELDS WITH GROUNDWATER LEVEL CONTROL SYSTEMS

In direct-seeding cultivation of rice, it is possible to save working time for growing and transplanting seedlings. In Hokkaido, where the management area of one farm is larger than that of other parts of Japan, the area of direct-seeding cultivation in large-sized paddy fields with groundwater level control systems has been increasing. Irrigation requirements increase in some cases of direct-seeding compared with the transplanting cultivation. To disseminate direct-seeding in an area it is necessary that the increases in irrigation requirements be within the permissible range of the irrigation of the area. The authors compared three cultivation methods: direct-seeding in non-puddled submerged paddy fields, direct-seeding in well-drained paddy fields, and transplanting cultivation, by using a large-sized block paddy field with the groundwater level control system facilities in Moseushi Town of Hokkaido. The following were clarified: 1) The difference in infiltration was small between the transplanting and direct-seeding cultivation methods. 2) The water supply volume, which is the sum of the irrigation requirement and the effective rainfall, of the three methods had very few differences in the period from the initial water intake and the re-submerging of the field because the groundwater level in the vicinity of the field was comparatively high and the infiltration was small. 3) The quantity of water intake during the period of shallow water management in direct-seeding cultivation is comparable to the puddling water requirement in transplanting cultivation.