Blended soil amendments: A viable strategy to reduce soluble phosphorus in soils

Phosphorus (P) loss from soils can contribute significantly toward P enrichment in water bodies, impairing water quality. Application of soil amendments is a viable strategy to decrease soluble P in surface soils. Since soluble P is reduced through different mechanisms that are amendment-specific, blended amendments could be a better approach than single amendment applications; however, very little information is available on blended amendment effects in reducing P loss from soils. We compared the effectiveness of gypsum (CaSO₄·2H₂O), Epsom salt (MgSO₄·7H₂O), and alum [Al₂(SO₄)₃·18H₂O] applied singly or blended in different ratios in reducing water-extractable P (WEP) and Mehlich-3 P of two soils (0- to 15-cm depth) with contrasting P status (Mehlich-3 P of 7.1 mg kg^-1 and 202 mg kg^-1) from the Red River Valley region in MB, Canada. Ten treatments used for the laboratory incubation study were unamended control, gypsum or Epsom salt at 2.5 or 5 Mg ha^-1, alum at 2.5 Mg ha^-1, and four blended treatments of gypsum: alum or Epsom salt: alum at 1:1 or 2:1. Treated soils were saturated and incubated for 2 weeks and analyzed for WEP (an indicator of risk of P loss) and Mehlich-3 P (plant-available P) concentrations. All amendments significantly reduced the WEP concentrations compared to control in both soils. The blended amendments, particularly gypsum-alum blends, performed better than unblended amendments in reducing the potential risk of P loss. Mehlich-3 P concentration was not influenced by amended treatments, suggesting no significant decrease in plant-available P with amendments in both soils.