Recent trends in phosphate balance nationally and by region in Japan

Abstract

A reduction in chemical phosphate (P) fertilizer application to farmland from 137.6 kg P ha⁻¹ in 1985 to 99.0 kg P ha⁻¹ in 2005 and in manure application from 42.4 kg P ha⁻¹ in 1985 to 32.8 kg P ha⁻¹ in 2005 did not reduce crop P uptake, which averaged 27 kg P ha⁻¹ over the period. Phosphate balance on farmland declined from 153.0 kg P ha⁻¹ in 1985 to 105.4 kg P ha⁻¹ in 2005 while livestock excreta disposal increased from 12.7 kg P ha⁻¹ in 1985 to 23.7 kg P ha⁻¹ in 2005. As a result, residual P associated with agriculture declined from 165.8 kg P ha⁻¹ in 1985 to 129.1 kg P ha⁻¹ in 2005. Phosphate utilization efficiency increased from 15.7% in 1985 to 20.1% in 2005. Median, minimum and maximum values of P flows by region showed similar trends. Phosphate input and withdrawal through crop production by region were not related to regional nitrogen (N) input and withdrawal through crop production. Although non-utilized P associated with agriculture has declined nationally and regionally, it is still higher than that in foreign countries, because of high chemical P fertilizer inputs and low crop yield withdrawal. Because soil P fertility was often sufficiently high previous large P surpluses, reducing P applications did not affect crop yields. Crop P uptake was less than half that of crop N yield. These results indicate that P inputs, especially by chemical fertilizer, for crop production could be reduced, thereby reducing negative environmental effects such as eutrophication of soil and water and conserving limited P resources.