Effects of Farming Practices on the Transfer of Phosphorus in Rural Catchments

Abstract

To better understand the role of agriculture in the eutrophication of surface waters, the spatial and temporal variation in P concentrations in streams and storm runoff was examined in relation to historic and current farming practices (upland pasture improvement, soil P accumulation, soil cultivations and fertiliser and manure inputs) and other sources of P (farmyards, road runoff and wastewater discharge) in a number of small rural catchments in England. In an upland pasture catchment and a lowland mixed farming catchment, soil P was the major source of P export rather than annual field operations which generally did not coincide with the main periods of hydrological connectivity. The majority of P transfer was in particulate form (>0. 45 pm), although field plot investigations suggested this form of P was relatively insensitive to differences in soil P fertility as compared to the dissolved P fraction, and may release P to the watercolumn even at low soil P concentrations. Three mitigation options (early sowing, reduced cultivations and tramline removal) for reducing soil particulate P transfer were compared at the field scale. All three options had positive effects. Early crop establishment was the most effective, but not consistently so, suggesting a combination of measures is required on farms. Analysis of 118 storm runoff samples showed that farmyard and road runoff, and runoff receiving wastewater (septic tank) discharges were more concentrated in P than surface and sub-surface runoff from agricultural fields. These sources also arrive more continuously through the year and therefore are potentially more ecologically damaging than runoff from farmed land. It is concluded that urbanisation maybe a greater threat to eutrophication than agricultural intensification even in small rural catchments and that effective, integrated catchment management requires collective social responsibility to tackle the multiple sources of P entering water and not just the targeting of the farming community.