A modified Ontario P index as a tool for on-farm phosphorus management

Reid, D. K. 2011. A modified Ontario P index as a tool for on-farm phosphorus management. Can. J. Soil Sci. 91: 455-466. The phosphorus index (P index) concept has gained wide acceptance as a tool to aid users in reducing P losses to surface water, but there is a wide range of potential users with differing goals on what the P index could or should do. To effectively change the behaviour of farmers who are applying fertilizer or manure to their fields requires a change in focus of the P index. This paper proposes a modified P Index that assesses the inherent risk of P loss to surface water from a given area separately from the risk of P loss from applied materials, to make it easier for farmers to use the output from the P index for management decisions. It also incorporates changes in index calculations to incorporate the risk of P losses through tile drains as well as overland flow, to reflect the differences in transport of dissolved versus particulate P, and to match the weightings of the P index factors to the relative risk of P loss from the landscape under Ontario conditions.