@article {Leytem89, author = {A. B. Leytem and J. T. Sims and F. J. Coale}, title = {On-farm evaluation of a phosphorus site index for Delaware}, volume = {58}, number = {2}, pages = {89--97}, year = {2003}, publisher = {Soil and Water Conservation Society}, abstract = {The contribution of phosphorus (P) to non-point source (NPS) pollution of surface and groundwaters is a serious environmental problem in Delaware. In 1999, the Delaware Nutrient Management Act was passed limiting application of P on {\textquotedblleft}high{\textquotedblright} P soils to a {\textquotedblleft}three year crop removal{\textquotedblright} rate or to the amount recommended by a University of Delaware P site index. The Delaware P site index was developed and evaluated on seven farms in Delaware, through a joint effort between the universities of Delaware and Maryland. Results showed that 78\% of fields evaluated were in the {\textquotedblleft}low{\textquotedblright} risk category, with the remaining 22\% falling into the {\textquotedblleft}medium{\textquotedblright} (6\%), {\textquotedblleft}high{\textquotedblright} (7\%), and {\textquotedblleft}very high{\textquotedblright} (9\%) risk categories. The components of the index found to have the greatest influence on P site index ratings were soil erosion, subsurface drainage, leaching potential, distance from field to surface water, soil test P and organic P application rates and methods. P site index ratings were found to vary by year, depending on manure applications, suggesting a need for yearly P site index evaluations or averages over a cropping rotation. The P site index worked well for identifying fields with differing relative potential risks of P loss; however, validation of these P loss assessments is needed to ensure that the risk categories assigned are sufficiently protective of water quality. Continual monitoring, analysis, and improvement of the P site index are needed to ensure that it remains a useful tool for P based nutrient management planning in the future.}, issn = {0022-4561}, URL = {https://www.jswconline.org/content/58/2/89}, eprint = {https://www.jswconline.org/content/58/2/89.full.pdf}, journal = {Journal of Soil and Water Conservation} }