D. Keith Reid1, Adam Hayes2, Christine Mary Brown3, Daniel Saurette1, Andrew Jamieson1, Kevin McKague3, Donald Hilborn3, Bonnie Ball4 and Deanna Nemeth5, (1)AESB, AAFC, Guelph, ON, Canada (2)Ontario Ministry of Agriculture & Food, Ridgetown, ON, Canada (3)Ontario Ministry of Agriculture, Food and Rural Affairs, Woodstock, ON, Canada (4)Ontario Ministry of Agriculture, Food and Rural Affairs, Stratford, ON, Canada (5)Ontario Ministry of Agriculture, Food and Rural Affairs, Vineland, ON, Canada
The P Index has been part of the NMAN nutrient management software program in Ontario since the late 1990s. It was modified from the Maryland P Index, following an additive model, and the output was restrictions on P application rates and setbacks from surface water. Since that time, the understanding of mechanisms for P loss have advanced significantly, which led to a review of the current P Index to create a more robust and accurate tool to identify areas of greatest risk for P loss to surface water. The proposed revisions include accounting for dissolved as well as particulate P losses, the impact of application method and timing on losses from applied P, and the net impact of tile drains on P movement from agricultural land. A component model is used to facilitate prediction of losses from various sources and through various pathways with the correct relative weighting.