Abstract
In order to minimize the environmental pollution of the Lake Biwa, rice has been cultivated under low imput of chemical fertilizer and agricultural chemicals since 2001 in Shiga-prefecture. Under these situations, the amount of nitrogen application is less than that in the traditional cultivation. Present status of the yield, dry matter production, or nitrogen balance between application and absorption in such a cultivation are not yet known so much. Therefore, the investigation were carried out to resolve those questions. Yield and dry matter production of the investigated low imput rice were not so high. But the yield of whole rice which includes traditional cultivation in Shiga-prefecture was 525.3kg/10a, and the yield were almost not changed since 2001. These indicate that the yield of low imput cultivation is approximately as same as that in traditional one. Dry matter production of the low imput rice was not so high. because of the shortage of the number of panicles. The amount of absorbed nitrogen by the low imput rice exceeded to that of application. Therefore, it may be considered that the severe decrease of soil fertility would occur according to long continuation of such cultural practice. The straw, whose dry weight is almost same as that of panicles weight and which contains considerable amount of nitrogen together with carbon, should be returned to the paddy field to maintain the soil fertility.
