Abstract
Water budgets in large-sized paddy fields with 3 different cultivation methods were measured in the Yokoyama district of Shiga Prefecture from 1995 to 1999, and these were compared to the water requirement plan in the district. Direct seeding culture in a flooded paddy field (DF), direct seeding culture in a well-drained paddy field (DW) and traditional transplanting culture (TC) were compared. The following results were obtained: i) At the early stage of irrigation, the direct seeding cultures (DF and DW) require more water than the TC. ii) The larger amount of water required in the DF was caused, to some extent, by a water distribution plan which was not suitable for the DF at seedtime. iii) After the early stage of irrigation, water demand for the DW tended to be much higher than that for the TC, while the DF was more variable than the others. iv) The water depth requirements in the TC and the DF seldom exceed the planned requirement. However, it would be necessary to enhance the planned water intake volume if an increase of the lot-management water requirement due to labor-saving is intended. v) The differences of cultivation types have no significant impact on effective rainfall.
