Beyond Environmental Soil Tests for Phosphorus – Entering the Regulatory Arena.

The use of soil phosphorus (P) tests as environmental indicators for the potential of nonpoint P pollution of ground and surface waters began more than 20 years ago and is now an established practice in many countries. In most, but not all, cases, soil P tests are incorporated into more complex approaches to assess the risk of P loss, such as the P Site Index or models such as AGNPS, EPIC, HSPF, REMM, and SWAT. Initially, the use of agronomic soil P tests (Bray P, Mehlich 1 and 3, Olsen P), or other “environmental soil P tests” (e.g., water soluble P, soil P saturation) for environmental purposes was done to provide guidance to help farmers and advisors from technical and regulatory agencies identify the most cost-effective “best management practices” to prevent nonpoint P pollution. However, nutrient management has gradually evolved in a more regulatory direction and has recently even become a central component of legal actions designed to mandate practices that prevent P loss. Given these changes, the soil testing community needs to address, in a systematic and proactive manner, the most appropriate means to use soil P tests in regulatory situations. This presentation analyzes the evolution of “environmental soil P testing”, summarizes current approaches now followed in the US and other countries, and provides recommendations for the future use of soil P tests in both advisory and regulatory settings where water quality protection is a primary goal.