Abstract
From 1991 to 2000, a rice cultivar, Koshihikari, was grown in the field, where either farmyard manure or chemical fertilizer was continuously applied. A minimal amount of herbicide and pesticide were applied only once after transplanting. Grain yield in the field with farmyard manure application alone was low owing to fewer spikes per plant. Farmyard manure may not supply enough nutrients for the production of enough tillers and spikes even by continuous application. Yield in the field with farmyard manure plus a small amount of chemical fertilizer was the highest though it fluctuated year by year. In the field with continuous application of a small amount chemical fertilizer without farmyard manure, spike number gradually decreased after several years, suggesting the lowering of soil fertility. In the field with continuous application of heavy fertilizer without farmyard manure, the yield was as high as that in the field with continuous application of farmyard manure together with a small amount of chemical fertilizer. It is concluded that continuous application of 200kg/a farmyard manure cannot raise the soil fertility enough to produce enough tillers and spikes for a high yield, but if a small amount of chemical fertilizer was applied together, we can obtain a relatively high yield without suffering from heavy panicle blast.
