Studies on the Irrigation Requirement in Direct Drilling on the Dried and Ponded Paddy Field

For two years, we examined and investigated the change of irrigation requirement of two expanded paddy fields (each 50 a) which were introduced both direct drilling methods on the dried and ponded paddy fields, and made clear the following matters. 1) The condition of irrigation water consumed every ten days showed the same tendency in each of two years and maximum peak of evapotranspiration (ET. ) coincided with maximum peak of temperature and duration of sunshine every ten days. 2) Quantity of percolation in direct drilling on the dried paddy field showed very large values at the beginning of irrigation (160 mm/10 days), then decreased gradually and after about one month became almost stable (40 mm/10 days). 3) In both A and B fields, irrigation water consumed by direct drilling on the dried paddy field was about three times as large as that of direct drilling on the ponded paddy field. Therefore, from the viewpoint of water saving only, direct drilling method on the ponded paddy field seemed to be reasonable. 4) In both direct drilling methods, consumed water in the B field was about 1.6―1.7 times as large as that of A field. It became clear that the difference mainly depended on the depth of groundwater table and the position of outlet among the characteristics of paddy field.