Organic Phosphorus Source Effects on Calcareous Soil Phosphorus and Organic Carbon

The loading, solubility, mobility, and plant availability of P is a growing environmental concern to regulators and planners of nutrient management plans, confined animal feeding operations, and wastewater land application permit sites. Insufficient information is available on how P reacts from different organic sources when applied to calcareous soils. A field study was conducted to determine the interactions among P application rate, source, extractability, and soil organic carbon (OC) concentration. A Portneuf silt loam (Coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids) topsoil and freshly exposed subsoil were fertilized with monocalcium phosphate (MCP), cheese whey, and dairy manure. Organic matter added with the whey did not influence soil OC concentrations whereas organic matter added with the manure doubled the subsoil OC and increased the topsoil OC concentrations. Bicarbonate and saturation paste extractable orthoand organic-P concentrations were linearly related to soil OC concentrations but were not related to the amount of orthoor organic-P added. All forms of P increased more per unit of added P in the order manure > whey > MCP and were correlated with the soil OC concentrations. These results suggest organic waste applications should be managed from :oil P test data rather than on P applica-