PHOSPHORUS LOSS IN AGRICULTURAL DRAINAGE - HISTORICAL-PERSPECTIVE ANDCURRENT RESEARCH

The importance of P originating from agricultural sources to the nonpo int source pollution of surface waters has been an environmental issue for decades because of the well-known rule of P in eutrophication. Mo st previous research and nonpoint source control efforts have emphasiz ed P losses by surface erosion and runoff because of the relative immo bility of P in soils. Consequently, P leaching and losses of P via sub surface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situa tions where environmentally significant export of P in agricultural dr ainage has occurred (e.g., deep sandy soils, high organic matter soils , or soils with high soil P concentrations from long-term overfertiliz ation and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present ov erviews 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 draina ge to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P lo sses in subsurface runoff.