Manuring and fertilization effects on phosphorus accumulation in soils and potential environmental implications

Abstract

Phosphorus application as manure to agricultural soils in intensive livestock farming and arable cropping systems often exceeds P offtake by crops. This surplus could lead to P accumulation in soils, making them long-term diffuse sources of P loss to water. We investigated the impact of a range of manuring and fertilization practices in intensive farming systems on the accumulation of P in soils, soil test phosphorus (STP), distribution of organic and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increases in both total soil P content and STP values (Olsen-P and Mehlich-3 P), as a result of P surpluses. The net total P accumulation in the soils across the sites ranged from 16 to 232 kg P ha −1 year −1. The effects of long-term P surpluses were a significant reduction in P-retention capacity and increase in DSSP. The sites investigated would attain 25% DSSP in 10–150 years, depending upon the size of P surplus and sorption capacity. A combination of large P surplus and low P-sorption capacity could saturate soils to 25% DSSP within 10–30 years. The values of Olsen (85 mg P kg −1) and Mehlich-3 (305 mg P kg −1) extractable-P predicted for the 25% DSSP are likely to result in environmentally significant P losses.