Trends of phosphate fertilizer demand and phosphate balance in farmland soils in Japan

We analyzed the trends in phosphate (P) demand from 1966 to 1999, estimated the P flow in farmland in 1997, and evaluated the risk of environmental damage in Japan. Chemical P fertilizer demand per unit farmland area increased from 106 kg ha(-1) in 1966 to 152 kg ha-1 at the end of the 1970s, then decreased 143 kg ha-1 after the mid 1980s to 117 kg ha(-1) in 1999. This trend reflected recommendations on the use of large inputs to increase soil fertility until the 1970s, and the reduction of production costs since the 1990s. In 1997, the amount of P applied to farmland soils in Japan was 6.3 times higher than crop uptake. Outflow from farmland was estimated to account for only 0.6% of the applied P. Most of the applied P remained in farmland soil. P in farmland soils increased the risk of eutrophication by flooding and surface run off. Seventy six percent of applied P was in the form of chemical fertilizer. Chemical fertilizer was applied at a higher rate to fruit and nut fields, vegetable fields, and industrial crop fields than to paddy fields. The remaining P resulted in a high availability P in fruit and nut fields and horticultural fields. The amount of P in livestock excreta corresponded to half of the amount of chemical P fertilizer applied. One-third of the livestock excreta was not utilized in 1997, which was the main source of environmental load associated with agriculture. Therefore, promotion and alternative use of livestock excreta are important to reduce the environmental load, while uneven regional distribution of livestock excreta makes it more to achieve this objective difficult. Maintenance of optimal soil fertility by using chemical P fertilizer and manure is important for saving limited P resources and for securing a low environmental risk.