Abstract
Field studies were carried out for 9 years to examine the effect of long-term application of green manure (sorghum, clotararia, pampas grass) on the yield of succeeding crops (potato and taro) and the physical and chemical properties of Dark Red Soil. The obtained results were: 1) The average fresh yields of sorghum and clotararia were 28 and 61 Mg ha^<-1>, respectively. Pampas grass collected from the grassland was 50 Mg ha^<-1>. These were cut and incorporated into soil by rotary tillage every September, and potato (Norin No.1) or taro (Ishikawa wasemaru) was planted about 3 months after incorporation. 2) The average yield of potato (8 times) was significantly (11-18%) higher for the plot incorporating green manure as compared to the control plot, whereas in the case of taro (2 times), there was no significant difference. 3) Total carbon, total nitrogen, and exchangeable K contents of the soil increased with the successive application of green manure. The increase rate of total carbon followed the order: pampas grass>sorghum>clotararia. It was suggested that 25 and 30% of the nitrogen in sorghum and pampas grass be incorporated into the soil, respectively. It was suggested that about 30% of the nitrogen be decomposed in the plot of clotararia. The increase rate of exchangeable K was 0.026-0.084 cmol(+)kg^<-1> per year. On the other hand, the amount of exchangeable Ca and Mg decreased. The decrease rates were 0.23-0.38 and 0.09-0.13 cmol(+)kg^<-1>, respectively. These results suggested that it is necessary to decrease the amount of sodium fertilizer and check the exchangeable Ca and Mg after the application of green manure. 4) The porosity of the soil increased and bulk density decreased with the successive application of green manure.
