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

Phosphorus application as manure to agricultural soils in intensive livesto ck farming and arable cropping systems often exceeds P offtake by crops. Th is surplus could lead to P accumulation in soils, making them long-term dif fuse sources of P loss to water. We investigated the impact of a range of m anuring and fertilization practices in intensive farming systems on the acc umulation of P in soils, soil test phosphorus (STP), distribution of organi c and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increa ses in both total soil P content and STP values (Olsen-P and Mehlich3 P), a s 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 i ncrease in DSSP. The sites investigated would attain 25% DSSP in 10-150 yea rs, depending upon the size of P surplus and sorption capacity. A combinati on of large P surplus and low P-sorption capacity could saturate soils to 2 5% DSSP within 10-30 years. The values of Olsen (85 mg P kg(-1)) and Mehlic h-3 (305 mg P kg(-1)) extractable-P predicted for the 25% DSSP are likely t o result in environmentally significant P losses. (C) 2001 Elsevier Science Ltd. All rights reserved.