Blended Soil Amendment Effects on Phosphorus Loss from Soils under Simulated Snowmelt Flooding

Phosphorus (P) accumulation in agricultural soils from long-term fertilizer and manure applications increases the risk of P mobilization into freshwater systems, contributing to eutrophication. In the Canadian Prairies, spring snowmelt over frozen soils creates anaerobic conditions, exacerbating the transport of dissolved reactive phosphorus (DRP) to surface waters. This research investigated the effectiveness of single and blended soil amendments in reducing P losses from high legacy P soils under simulated snowmelt flooding conditions. Two complementary laboratory studies were conducted using agricultural soils from southern Manitoba. The first study employed packed soil incubations to evaluate fifteen treatments across six soils, including an unamended control, six single amendments at different rates of alum [KAl(SO4)2.12H2O], ferric chloride (FeCl3), gypsum (CaSO4.2H2O), and magnesium sulfate (MgSO4), plus eight blended combinations. The second study used intact soil monoliths from four sites to compare gypsum, ferric chloride, and their 1:1 combination. Results demonstrated that ferric chloride-based treatments were consistently the most effective across soil types. In packed soils, single amendment of ferric chloride achieved maximum DRP reductions of 64%, while blended amendments containing ferric chloride achieved reductions up to 89%. The monolith study confirmed these findings, with ferric chloride reducing floodwater DRP by 93-99%. Calcium and magnesium-based amendments showed soil-dependent effectiveness, with gypsum achieving 31-56% reductions in the monolith study. Blended amendments did not provide substantial advantages over single ferric chloride applications. These findings suggest that ferric chloride represents a viable single-amendment strategy for mitigating snowmelt-driven P losses from Prairie agricultural soils, offering practical implications for water quality protection in cold climatic regions.