Phosphorous leaching from coarse-textured soils amended with inorganic or organic fertilizers

Non-point source pollution of surface waters with phosphorous (P) transported from agricultural soils has emerged as a major environmental issue in the last decade. Regulations limiting P accumulation in surface soils have been established to protect surface water quality. Yet, little information is available on the quantities of P that may leach through soils and the factors influencing P leaching in agricultural soils. One important factor may be the type of fertilizer P applied, since it is known that P solubility varies among fertilizer sources. The purpose of this thesis was to quantify P leaching in soils amended with inorganic and organic fertilizers.In a field study, we found that the fertilizer P source (triple superphosphate, composted cattle manure, or a mixture of the two) did not affect soil test P concentration, the degree of soil P saturation, or P leaching in a sandy-loam soil. The soil test P level in the 0--15-cm depth (146 mg P kg -1) exceeded the critical limit of 66-mg kg-1 established in Quebec, and ortho-P and DOP concentrations in leachates collected from piezometers were generally higher than the provincial water quality standard of 0.03 mg P L-1. If transported from our study site, P leached through this coarse-textured soil could pose a threat to groundwater and surface water quality.These findings were verified in the laboratory with two coarse-textured soils. We found that more NO3-N and DON were leached from soils receiving inorganic N and P fertilizers than composted cattle manure, but the amounts of ortho-P and DOP leached were not affected by fertilizer sources. In coarse-textured soils, the quantities of P leached can be substantial, but depends more on soil characteristics than the fertilizer P source