Organic Phosphorus Can Make an Important Contribution to Phosphorus Loss from Riparian Buffers

Abstract

Core Ideas Forested and vegetative buffers can retain P runoff from adjacent fields. High concentrations of molybdate unreactive P were detected in soil water extracts. With time, these buffer soils can be a source of soluble inorganic and organic P. High microbial activity in buffer soils suggests biologically mediated P release. Vegetative buffer strips (VBS) and managed or unmanaged riparian zones between the edge of field and receiving watercourse are widely adopted conservation practices aimed at reducing nonpoint nutrient pollution. However, their effectiveness at decreasing phosphorus (P) loss has been mixed. This study investigated the effectiveness of a VBS and a forested riparian zone (FRZ) in decreasing P loss from pasture soils receiving swine manure and aimed to determine the potential factors controlling P release, using water extractable P (WEP) as a proxy for P loss. The inorganic WEP concentrations were significantly greater in the fertilized pasture zone soils than the VBS or FRZ soils. However, there was no significant difference between the field and riparian soils for total WEP due to increased contribution from organic WEP in these soils. Degree of P saturation, which is a function of soil test P, was a good predictor of inorganic WEP, but not organic WEP, where the variation in concentrations was better explained by variables involved in biotic P release.