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 pl ans, confined animal feeding operations, and wastewater land application pe rmit sites. Insufficient information is available on how P reacts from diff erent organic sources when applied to calcareous soils. A field study was c onducted to determine the interactions among P application rate, source, ex tractability, and soil organic carbon (OC) concentration. A Portneuf silt l oam (Coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids) topsoil and freshly exposed subsoil were fertilized with monocalcium phosph ate (MCP), cheese whey, and dairy manure. Organic matter added with the whe y did not influence soil OC concentrations whereas organic matter added wit h the manure doubled the subsoil OC and increased the topsoil OC concentrat ions. Bicarbonate and saturation paste extractable ortho- and organic-P con centrations were linearly related to soil OC concentrations but were not re lated to the amount of ortho- or organic-P added. All forms of P increased more per unit of added P in the order manure > whey > MCP and were correlat ed with the soil OC concentrations. These results suggest organic waste app lications should be managed from soil P test data rather than on P applicat ion rates.