Estimation of rock phosphate application using radio isotop technique on agricultural land

More than 80 percent of arable land in Japan represent as volcanic soil. One of the most important need in the cultivation of the soil is to increase the phosphorus (P)supply to crops. The use of phosporic rock (PR) directly as source of P has been studied by many researchers on account of the present of local deposits that imply lesser cost comparatively with commercial imported fertilizer. With the utilization of isotopic technique using isotopic P at the power of 32 dilution method, the appraisal of these native sources of P, compared to the standard commercial fertilizers has been possible. One field and one greenhouse experiments were carried out. The results showed that every kg of P as TSP (triple superphosphate) equal to 11 kg P as PR and 3 kg P as CPR (Concentrated Phosphoric Rock). Finally, in the field application to soils with high P retention, it should be along with another more soluble P source acting as a starter