Phosphorus Status of Forest and Agricultural Soils from a Watershed of High Animal Density

Abstract

Abstract The objective of this work was to study the impact of animal density on P status in soils from the Beaurivage River Watershed, Quebec, Canada. Twenty‐five samples from A, B, and C horizons from the five most representative soil series were taken from sites under forest, hay fields of dairy farms, and farms with a known surplus of on‐farm manure N (SN). Profiles were characterized for water‐soluble P (P w ), Mehlich‐3 extractable P (M3P), and fractions. The P w was 3.6 times larger in agricultural than in forest soils in the A horizon. Excessive amounts of 66.5 mg kg −1 of M3P and of 95 mg kg −1 Resin‐P were found in the plow layer of agricultural soils and M3P was increased, on average, by 10 mg kg −1 in the C horizon compared with forest soils. The accumulation of added P has lead to an increase in labile (Resin + NaHCO 3 + NaOH‐P o ) P pools in the A horizon, whereas the resilient (total labile P) pools were the major sinks in B and C horizons. For SN farms, total P was increased by 435 mg kg −1 in the A, 86 mg kg −1 in B, and by 141 mg kg −1 in the C horizon compared with forest soils. Dairy farms soils had labile P contents similar to those from SN farms but were less enriched in resilient‐P i forms. The observed large P loads in surface horizons and P w increases in the subsoil of the agricultural soils probably contribute to the contamination of surface waters in this watershed.