Changes afoot in the Phosphorus Index

American Society of Agronomy: Phosphorus (P) is both an essential nutrient in agricultural fields and a contributor to poor water quality in surface waters. To encourage improved P management in fields, the P Index was proposed as a risk assessment tool in 1992. After 20 years of use, modifications, and growing pains, does the P Index accurately assess the risk of P loss?

...“The objective of the original P Index was to identify fields that had high risk of P loss and then guide producers’ decisions on implementing best management practices,” says Nathan Nelson, ASA and SSSA member and co-author of the special section’s introductory paper. “The P Index has developed into a widely used tool to identify appropriate management practices for P application and fields suitable for such application.”

...Because the P Index can be used to guide conservation practices, the USDA-National Resource Conservation Service (NRCS) adopted it as part of their management planning process. The NRCS, then, left it up to each state to develop their own P Index best suited for their environments and concerns.

...The inconsistencies of indices across states, along with a perceived lack of improvement in water quality in some regions, are now bringing the accuracy of the P Index into question. With different calculations in place, a set of factors may be categorized as low risk in one state and medium, or even high, risk in another. These discrepancies become especially obvious along state borders.

Researchers understand the need to improve P indices and have made it a priority to base any changes on sound scientific data....

Tractors a Texas field in 1972