Using soil phosphorus profile data to assess phosphorus leaching potential in manured soils

Transport of P by subsurface flow pathways can be an important mechanism of P transfer from land to water, particularly in manured soils that are artificially drained. This study was conducted to determine whether detailed description and interpretation of soil P profile data provide adequate insight into P leaching potential. Evidence of P translocation within soil profiles of a tile-drained Buchanan (fine-loamy, mixed, semiactive, mesic Aquic Fragiudult)-Hartleton (loamy-skeletal, mixed, active, mesic Typic Hapludults) catena was assessed by measuring oxalate-extractable P, P sorption saturation, Mehlich-3 P, water-extractable P in bulk and clay film samples obtained from individual horizons. Tile-drain monitoring and column leaching experiments were conducted to evaluate interpretations derived from soil P profile data. Soil P fractions were not correlated with P losses in lysimeter studies, indicating the limited potential of using soil profile P data for quantitative prediction of leaching losses. Application of manure to the soil surface resulted in significant increases in leachate P concentrations from the lysimeters. Soil profile P data did, however, provide some evidence of long-term P leaching. While bulk horizon samples did not indicate significant long-term P translocation to soil depths corresponding with artificial drainage, some clay film samples had significantly elevated oxalate P, P sorption saturation and Mehlich-3 P at lower depths. Elevated P concentrations in clay films may be associated with preferential transport of P along soil macropores, although, not all clay films sampled in this study were necessarily associated with active macropores. Thus, soil P profile data appear to provide limited insight into P leaching potential.