Assessing the efficacy of alternative phosphorus sorbing soil amendments

Concern over the contribution of agricultural phosphorus (P) to fresh water eutrophication has focused attention on practices that decrease P losses from agricultural soils. At present, there are few management options for soils with P levels in excess of crop P requirements other than restricting P applications. This study assesses various readily available materials as possible P Sorbing Soil Amendments (PSSAs) by comparing their near- and long-term effects on soil P solubility and potential availability to runoff with their impact on plant available P. Specifically, anthracite refuse ash, bituminous refuse ash, by-product gypsum (CaSO4), siderite (FeCO3), steel processing sludge, water treatment residual, and wollastonite (CaSiO3) were incubated in three acidic and one neutral loam soils for 21 and 120 days to compare starting and ending water extractable soil P (WEP) and Mehlich-3 P concentrations. Across all soils, bituminous refuse ash, by-product gypsum, and water treatment residual decreased WEP consistently at the lowest rates of application without lowering Mehlich-3 P to less than crop requirements. In addition, no significant difference in WEP and Mehlich-3 P was observed for by-product gypsum between the 21-day and 120-day incubation periods, indicating that sorption reactions induced by this material are both rapid and stable with time. Anthracite refuse ash, siderite, steel processing sludge, and wollastonite were ineffective at decreasing WEP in soil at practical application rates. Results support the use of by-product gypsum and water treatment residual on acidic and neutral soils representing areas of high P loss potential.