Phosphorus accumulation in Canadian agricultural soils over 30 yr

Abstract

Phosphorus (P) loss to freshwater is a key driver of eutrophication, and understanding the scale and spatial distribution of potential P sources is a key pre-requisite for implementing policies for P management to minimize environmental impacts. Soil test P (STP) is a useful indicator of the accumulation of P in soils, but these data are not readily available for most agricultural land in Canada, so the cumulative P balance (P inputs as manure or fertilizer minus removal of P in crops) is calculated as a proxy for this value. Cumulative P balance is an important calculation within the indicator of risk of water contamination by P, so allocations of manure and fertilizer P to cropland were updated within the calculation of P balance, and for Ontario, data from 1961 to 1980 were added to account for P applications during that period. The STP concentrations were calculated from the resulting cumulative P balances. When compared with reported STP concentrations, the predicted concentrations showed a statistically significant regression at the national (R2 = 78%) and provincial scale (Ontario, R2 = 36%; Prince Edward Island, R2 = 36%; Manitoba, R2 = 72%; British Columbia, R2 = 40%). There was significant variation in the cumulative P balance across Canada, with the highest values corresponding with areas of high livestock density, whereas large zones of P deficit were detected across the Prairies.