Relationships among phosphorus concentrations and soil properties and land use in an agricultural watershed

The U.S. Environmental Protection Agency's watershed approach to address impacts of nonpoint source pollution on water quality uses the Total Maximum Daily Load (TMDL) concept. TMDL watershed characterization for phosphorus (P) encompasses P loadings, transport processes, and total P in streams. The objective was to do preliminary assessments of the P loadings for sources and soil P distribution through relationships among P concentrations, soil properties and land use in an agricultural watershed. Soil samples were taken and analyzed by agronomic soil P tests, Mehlich III, Olsen, and Total P by Ignition. Land use and geology were the major influences of P distribution. Swine unit land use dominated and influenced P distribution, regardless of soil test method. Interior Flatwoods region dominated P loadings for all soil tests, while forest land use dominated total P loadings. Precise knowledge of sample locations and historical land use would improve P distribution and source identification.