A statewide assessment of the impacts of phosphorus-index implementation in Pennsylvania

Abstract

Phosphorus (P) based nutrient management regulations may affect the viability of agricultural enterprises in Pennsylvania. Identification of areas likely to be affected by impending P-based regulations will allow regulators and conservation officials to better target technical and financial assistance. A statewide GIS analysis based on an extensive soil testing database and available geospatial data (including land cover, streams, and livestock density) found that various regions of Pennsylvania would be affected by the P-index restrictions for different reasons. In the southeast and parts of the northeast, high soil test P levels associated with intensive animal agriculture required a full assessment of P source and transport factors under the P-index. In north- and south-central and southwest Pennsylvania, the P-index assessment was required because of the proximity of much of the region’s farmland to surface waters. Additionally, nearly half of agronomic soil samples exceeded the optimum P level for crops, suggesting widespread over fertilization and an ongoing build up of soil P stocks. Soil P was found to increase with increasing animal density and the highest animal density areas had a large number of nutrient impaired streams. When samples were separated based on cover type, croplands exhibited the highest P levels, followed by grasslands and then pastures. Finally, a weighted combination of the percentage of soil samples exceeding 200 ppm P and the proportion of agricultural lands within 150 ft (45.7 m) of streams indicated that southeastern Pennsylvania, especially Lancaster County, would be most affected. How farm operators adapt to P-based nutrient management, via on- and off-farm strategies, will determine the severity of the impact and the necessity of government assistance.