Study on the improvement of fertilizer dressing and soil management in the rice field

Major part of nitrogen and phosphorus in the harvested rice plants was proved to be derived from soil nutrients by our field tracer experiments using 15-N and 32-P, even under heavy dressing of ammonium sulfate and superphosphate of over 75 kg per hectare in terms of N and P₂O₅ respectively. It fits quite nicely to Japanese farmer's common understanding, that the upland crops grow on the basis of fertilizer, and paddy rice on soil fertility. The Japanese rice soils, particularly under waterlogged conditions in summer, liberate rich nutrients from the organic matter, and the fertility of soils presents continuous supply of nitrogen and phosphorus throughout the rice Plant life.