A tool developed by USDA scientists can help agribusiness model phosphorus loss in runoff and determine ways to reduce these losses.

The Phosphorus Index was originally a simple management tool developed to gauge the risk of phosphorus losses from agricultural fields. The original index has since been modified by individual states to incorporate local variations in soils, climate, management and water quality goals. This resulted in widely different state-by-state phosphorus indices that were sometimes defined more by political boundaries than by watersheds or other regional variations.

To reduce these state-by-state discrepancies, lead Agricultural Research Service scientist Peter Vadas and colleagues developed the Annual Phosphorus Loss Estimator (APLE), a spreadsheet program that predicts field-scale phosphorus loss in runoff for a whole year. The revamped program can also be used in many different states to quantify field-scale phosphorus loss and soil phosphorus changes over 10 years for a given set of runoff, erosion and management conditions.

ARS is the USDA‘s chief intramural scientific research agency.

The team showed that APLE could reliably quantify phosphorus losses in runoff for many different situations and could produce more reliable estimates than some existing phosphorus indexes. Vadas also has been adapting APLE to simulate phosphorus loss from pastures grazed by beef and dairy cattle, and from barnyards and exercise lots on cattle farms.

With these improvements, APLE can be used to develop whole-farm estimates of phosphorus losses and the most effective strategies for reducing phosphorus losses from cattle farms. These practices could include barnyard improvements for capturing discharge, soil conservation practices that reduce erosion, or manure application practices that reduce exposure to runoff water.

APLE is free to download, with supporting technical documentation and a user’s manual.