Multi-Field Assessment of Riparian Buffer Effectiveness in Mitigating Subsurface Phosphorus Losses.
C. R. Bond, John Havlin, and Rory Maguire. North Carolina State Univ, Dept of Soil Science, PO Box 7619, Raleigh, NC 27695
The Phosphorus Loss Assessment Tool (PLAT) utilizes the Mehlich-3 P (M3P) soil test, and other parameters, to indicate the potential risk of surface and subsurface P losses to nearby waters from agricultural fields. The PLAT recognizes soil-dependent linear relationships between soluble P and M3P, and does not recognize the potential for a soil to become P saturated. Beyond P saturation, soluble P increases at greater rates per unit increase in M3P. While riparian buffers are an effective best management practice to attenuate surface P losses, limited documentation exists regarding the potential for riparian buffers to attenuate subsurface P losses via lateral transport. Our objectives were to validate the use of M3P and the M3P saturation ratio [P/(Fe+Al)] to predict P leaching in North Carolina coastal plain soils and evaluate riparian buffers for attenuating subsurface P losses from high-P fields. Coastal Plain soils that had received swine waste and represented various PLAT soil management groups and leaching potentials were selected for study. Field sampling grids consisted of three 73.2-m transects (18.3 m apart) with five cores per transect. Each transect consisted of three soil cores (168 cm deep) collected in the field, one at the field edge, and one 18.3 m into the buffer. Soil-dependent M3P saturation ratios (0.05 to 0.21) were proven indicators of P leaching, wherein P accumulated at depths in the profile exposed to the water table. Spatial interpolation of M3P saturation ratio data with depth across field sampling grids indicated the risk of subsurface lateral P loss was the least in mineral soils and greatest in organic soils. The proposed adoption of the M3P saturation ratio by the PLAT and the consequential impacts of its implementation will be discussed.