Phosphorus loss in agricultural drainage: Historical perspective and current research

The importance of P originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well-known rule of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long-term overfertilization and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestern USA (Indiana), and eastern Canada (Quebec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in subsurface runoff.