Phosphorus sorption and desorption indices in soil

Abstract

Abstract Information about phosphorus (P) sorption and desorption indices in soils is useful for environmental evaluations. The objective of this study was to develop P sorption and desorption indices for soils in the Beaurivage River watershed, Quebec, Canada. Thirty samples from the A, B, and C horizons of soils of the five main soil series were taken from sites under forest, dairy farms, and farms with a known surplus of manure. The maximum P sorption capacity (M) was estimated by a 48 h contact with 0.005M CaCl2 solutions of increasing P concentration while P desorption was measured in water (Pw). The P sorption index (Psi) was measured by contact of 1.5 g P/kg soil for 40 h in 0.01M KCl at a soil to solution ratio of 1:40. Regression analysis was used to generate equations predicting M, Psi, and Pw from readily available data on soil chemical and physical properties. The maximum P sorption capacity (M) was very closely related to the Psi (r>0.97**) in all horizons. The M and Psi sorption parameters were related to organic C (OC), Mehlich 3‐extractable P (M3P), and ammonium oxalateextractable Fe (FEOX) and Al (ALOX) in the A horizon; to M3P, ALOX, and the sand content in the B horizon; and to OC and ALOX in the C horizon. The Pw was related to pH, OC, M3P, exchangeable Ca in the A horizon; to M3P and sand content in the B horizon; and to pH, M3P, and FEOX in the C horizon. The relatively low coefficients of correlation and the close correlation found between M and Psi suggest that the latter should be experimentally measured rather than predicted to gain information on the P sorption potential of the soils from this watershed. The results of the present study indicate the M3P can be used in conjunction with other readily available soil data to predict the P desorbability of vulnerable watersheds.