Abstract
The actual state of phosphate application in arable farming in Japan was analyzed by using statistical data collected by the Statistics and Information Department, Ministry of Agriculture, Forestry and Fisheries. The amounts of phosphate in organic fertilizers and composts were expressed as those of chemical fertilizer equivalents (CFE phosphate) by multiplying the total phosphate contents by the phosphate efficiency factors, which represent the efficiency of organic fertilizer and compost phosphate in comparison with chemical fertilizer phosphate to crop growth. 1) The amounts of CFE phosphate applied have already been attained to the level to get the maximum yields in most of the crops. But outdoor eggplant and outdoor cucumber showed the higher yields in response to the higher application of CFE phosphate and showed no sign of yield decrease even with the application of 1,400 kg P_2O_5 ha^<-1> of CFE phosphate. 2) CFE phosphate derived from composts in total amounts of CFE phosphate applied shared in average 35% in outdoor vegetables, 34% in greenhouse vegetables, 33% in fruit trees and 18% in other crops. These high shares indicate the importance of taking into account phosphate from composts in fertilizer planning. 3) The rates of phosphate absorbed in top of crops to total CFE phosphate applied (absorption efficiency) were in average 9% in outdoor vegetables, 12% in greenhouse vegetables, 10% in fruit trees and 18% in other crops than paddy rice. Therefore, the amounts of CFE phosphate not absorbed in crops were very high with the highest case of 687 kg P_2O_5 ha^<-1> in greenhouse sweet pepper. The results indicated that higher absorption efficiencies of phosphate could be gained by lowering the phosphate application rate without a yield decrease. 4) The absorption efficiencies of paddy rice were estimated to be about 30% in 1970 and thereafter gradually increased to 40% in 1998. This was speculated to have been caused both by the accumulation of available phosphate in paddy soil and the reduction of the amounts of phosphate fertilizer applied after 1987. 5) By using the data of soil monitoring by Ministry of Agriculture, Forestry and Fisheries, the relationship was obtained, which indicated that in average 1 mg P_2O_5 100 g soil^<-1> of Truog phosphate was increased per 213 kg P_2O_5 ha^<-1> of CFE phosphate not absorbed in rice plants during 1979 and 1998 in paddy soils.
