Agricultural phosphorus and water quality: sources, transport and management

Authors

• Andrew Sharpley USDA-ARS, Pasture Systems and Watershed Management Research Laboratory, Curtin Road, University Park, Pennsylvania 16802-3702, USA
• William Gburek USDA-ARS, Pasture Systems and Watershed Management Research Laboratory, Curtin Road, University Park, Pennsylvania 16802-3702, USA
• Louise Heathwaite Department of Geography, University of Sheffield, Winter Street, Sheffield, S1O 2TN, United Kingdom

DOI: https://doi.org/10.23986/afsci.72855

Abstract

Freshwater eutrophication is usually controlled by inputs of phosphorus (P). To identify critical sources of P export from agricultural catchments we investigated hydrological and chemical factors controlling P export from a mixed land use (30% wooded, 50% cultivated, 20% pasture) 39.5-ha catchment in east-central Pennsylvania, USA. Mehlich-3 extractable soil P, determined on a 30-m grid over the catchment, ranged from 7 to 788 mg kg-1. Generally, soils in wooded areas had low Mehlich-3P (<30 mg kg-1), grazed pasture had Mehlich-3 P values between 100 and 200 mg kg-1, and cropped fields receiving manure and fertiliser applications were in most cases above 200 mg kg-1. Average P concentrations for ten storms during 1996 decreased 50% downstream from segment 4 to segment 1 (catchment outlet). Flow-weighted streamflow P concentrations were more closely related to the near-stream (within 60 m) than whole catchment distribution of high-P soils. This suggests that near-stream surface runoff and soil P are controlling P export from the catchment. Remedial measures should be targeted to these critical P source areas in a catchment. Measures include source (fertiliser and manure application) and transport management (reduce surface runoff and erosion).