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United States Department of Agriculture

Agricultural Research Service


item Sharpley, Andrew

Submitted to: Agricultural Research Service Station Bulletin
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2000
Publication Date: 9/1/2000
Citation: Sharpley, A.N. 2000. The phosphorus index: assessing site vulnerability to phosphorus loss. Agricultural Research Service Station Bulletin. 255-281.

Interpretive Summary: Inputs of phosphorus are essential for profitable crop and livestock agriculture. However, phosphorus export in watershed runoff can accelerate the eutrophication of receiving fresh waters. The specialization of crop and livestock farming has created regional imbalances in phosphorus inputs in feed and fertilizer and output in farm produce. In many of these areas, ,soil phosphorus exceeds crop needs and has enriched surface runoff with phosphorus. Several states have tried to establish general threshold soil phosphorus levels above which the enrichment of runoff phosphorus becomes unacceptable. However, threshold soil phosphorus criteria will be of limited value unless they are integrated with site potential for runoff and erosion. In cooperation with research scientists, the USDA, Natural Resource Conservation Service has developed a simple phosphorus index as a screening tool for use by field staff, watershed planners, and farmers to rank the vulnerability of fields as sources of phosphorus loss in surface runoff. The index accounts for and ranks source and transport factors controlling phosphorus loss in surface runoff and sites where the risk of phosphorus movement is expected to be higher than others. The index is intended for use as a tool for field personnel to easily identify agricultural areas or practices that have the greatest vulnerability to phosphorus loss and allow farmers more flexibility in developing remedial strategies.

Technical Abstract: Phosphorus (P) is an essential element for plant and animal growth and its input to agriculture is necessary to maintain profitable crop and animal production. However, P inputs to fresh waters can accelerate eutrophication. Environmental concern has forced many states to consider the development of recommendations for P applications and watershed management based on the potential for P loss in agricultural runoff. The risk of such loss depends on both source (added fertilizer and manure, soil P) and transport factors (erosion and surface runoff). Fields at high risk are those where areas of high P application or soil P coincide with zones of active surface runoff or erosion. A P index has been developed to rank field vulnerability to P loss so that high risk fields may be identified for site-specific management. The index provides a framework that can be regionally adapted to prevailing topography, geology, and climatic conditions and requires only readily available data.

Last Modified: 06/24/2017
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