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

Abstract

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.

Estimation of cadmium load on Japanese farmland associated with the application of chemical fertilizers and livestock excreta

“…High-analysis compound fertilizer was the largest source of Cd (4,157 kg Cd) followed by multi-phosphate (1,277 kg Cd). Mishima et al (2003) by multiplying the values by the Cd load per phosphate, because the amount and types of fertilizers were unknown. Cd concentration in livestock excreta.…”

“…Cd concentration in livestock excreta. Cadmium concentration in livestock excreta was estimated based on the amount of total, utilized, and disposed phosphate in excreta from each type of livestock (dairy cattle, beef cattle, pigs, layers, broilers) (Mishima et al 2003) and the Cd concentration per phosphate in livestock excreta according to Orihara et al (2002), because the fresh or dry weight of the livestock excreta was unknown. The Cd concentration per phosphate was used to convert the fate of phosphate in livestock excreta indicated by Mishima et al (2003) into the amount of Cd and was used to determine the changes in the Cd load will change when non-utilized livestock excreta were used as a substitute for chemical fertilizer.…”

“…Table 1) in demand was 7,001 kg Cd, accounting for 99.7% of the total Cd amount in all the fertilizers, these fertilizers were the main contaminants. To estimate the Cd load through phosphate fertilization for crops using the data supplied by Mishima et al (2003), the Cd load per phosphate was calculated to be 11.83 mg Cd kg-1 Pp 5 based on the total Cd load associated with the application of phosphate fertilizers and compound fertilizers (7 ,001 kg Cd) and the phosphate demand in 1997 (592 Tg) (MAFF 2002).…”

“…The rate of Cd load in relation to phosphate application (hereafter referred to as "per phosphate") was calculated by dividing the total Cd concentration in phosphate and compound fertilizers by the phosphate demand in Japan (MAFF 2002). Cd load in 6 crop types (paddy rice; potatoes, pulses, and cereals; vegetables; fruits and nuts; industrial crops; and forage crops) was estimated from the chemical phosphate fertilizer application for the crops indicated by Mishima et al (2003) by multiplying the values by the Cd load per phosphate, because the amount and types of fertilizers were unknown.…”

“…Our objective was to investigate the annual Cd load on Japanese farmland originating from chemical fertilizers and livestock excreta for 1997, as an extension of the study of Mishima et al (2003) on phosphate flow for 1997, because it is well known that the Cd load is as sociated with phosphate use (Sugo 1977;Zanders et al 1999) and there are no data about the total amount of chemical fertilizer use for types of crops as well as livestock excreta use and disposal on a fresh or dry weight basis. We also compared the Cd load with the estimated total Cd amount in farmland soil to examine the potential of an increase in the Cd concentration.…”