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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #103871
Title: IDENTIFYING CRITICAL SOURCES OF PHOSPHORUS EXPORT FROM AGRICULTURAL WATERSHEDS

Author
item Weld, Jennifer
item Sharpley, Andrew
item BEEGLE, DOUGLAS - PENN STATE UNIVERSITY
item Gburek, William

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2000
Publication Date: 1/30/2001
Citation: Weld, J.L., Sharpley, A.N., Beegle, D.B., Gburek, W.J. 2001. Identifying critical sources of phosphorus export from agricultural watersheds. Nutrient Cycling in Agroecosystems. 59:29-38.

Interpretive Summary: Agricultural runoff accounts for much of the phosphorus (P) input to and accelerated eutrophication of the fresh waters of upper Chesapeake Bay. In much of the Chesapeake Basin, manure produced by livestock operations are a major source of nutrients to farm systems. Because manure applications are normally based on N, considerably more P is added to the soil than is removed in harvested crops; the result is a buildup of soil P increasing the potential for P loss to the Bay. Several states have tried to establish general threshold soil P levels above which the enrichment of runoff P is unacceptable. However, threshold soil P criteria alone is of limited value, unless integrated with site potential for runoff and erosion. In cooperation with research scientists, the USDA, Natural Resource Conservation Service, has developed a simple P index as a screening tool for use by field staff, watershed planners, and farmers to rank the vulnerability of fields as sources of P loss in surface runoff. The index accounts for and ranks source and transport factors controlling P loss in surface runoff and sites where the risk of P movement is highest. The index is a tool intended for use by field personnel to easily identify the most likely agricultural source areas or practices and provide farmers more flexibility in developing P loss control strategies.

Technical Abstract: Surface runoff accounts for much of the phosphorus (P) input to and accelerated eutrophication of the fresh waters. Several states have tried to establish general threshold soil P levels above which the enrichment of surface runoff P becomes unacceptable. However, little information is available on the relationship between soil and surface runoff P, particularly for the northeastern United States. Further, threshold soil criteria will be of limited value unless they are integrated with site potential for runoff and erosion. In response, the Natural Resource Conservation Service (NRCS) developed a P Index (PI), which ranks the vulnerability of fields as sources of P loss in runoff, based on soil P, hydrology, and land use. This study evaluated the relationship between soil and surface runoff P in a study watershed in central Pennsylvania. The relationship was then incorporated into the (PI), and its impact on the eidentification of critical source areas within the watershed was examined. Using simulated rainfall (5 cm/h for 30 min), the concentration of dissolved P in surface runoff (0.2 2.1 mg/l) from soils was related (r2=0.67) to Mehlich-3 estimate soil P (30-750 mg/kg). Using an environmentally-based soil P threshold level of 450 mg/kg determined from the soil-runoff P relationship, the PI identified and ranked areas of the watershed vulnerable to P loss. The vulnerable areas were located along the stream channel, where areas of runoff generation and areas of high soil P coincide, and where careful management of P fertilizers and manure should be targeted.