Comparison of phosphorus loss estimation tools at predicting nutrient transport in humid regions with undulating topography.

Phosphorus (P) site assessment tools are used to determine the potential for a particular agricultural field to export P to a surface water body. The Phosphorus Index is one of the most widely adopted P site assessment tools in the country and is being utilized by water resource managers to help determine the relative risk of nutrient loss from agricultural fields and design P management strategies. However, the use of simple empirical models in the P-Index could possibly be improved to account for dynamic P loss mechanisms in areas with complex topography and variable source area (VSA) hydrology. Using the Vermont P-Index and TopoSWAT, scenarios of varying P management strategies were modeled for corn silage production fields in a small watershed (360-ha) located in Addison County, Vermont. TopoSWAT and P-Index outputs were compared to one another across areas of differing topographic wetness class to investigate the effects of topography on estimated P loss in agricultural watersheds in the Northeastern U.S. Results from this study will inform potential changes to P-Indices that aim to better represent humid regions with undulating topography. Preliminary results and conclusions from this study will be presented