PT  - JOURNAL ARTICLE
AU  - A. B. Leytem
AU  - J. T. Sims
AU  - F. J. Coale
TI  - On-farm evaluation of a phosphorus site index for Delaware
DP  - 2003 Mar 01
TA  - Journal of Soil and Water Conservation
PG  - 89--97
VI  - 58
IP  - 2
4099  - http://www.jswconline.org/content/58/2/89.short
4100  - http://www.jswconline.org/content/58/2/89.full
AB  - 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 “high” P soils to a “three year crop removal” 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 “low” risk category, with the remaining 22% falling into the “medium” (6%), “high” (7%), and “very high” (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.