A New User-Friendly Tool for Quantifying Phosphorus Loss From Agricultural Systems.

Loss of phosphorus from agricultural fields to aquatic systems can accelerate eutrophication. Decades of research have greatly increased the scientific understanding of processes controlling agricultural phosphorus availability and transport. However, there is a lack of user-friendly decision tools to rapidly and accurately quantify phosphorus loss from agricultural systems. We developed the Annual Phosphorus Loss Estimator (APLE) to serve this purpose. APLE is a spreadsheet model that predicts annual phosphorus loss in surface runoff from erosion, soil, and fertilizer or manure for a wide variety of agricultural systems. APLE also simulates 10 years of soil phosphorus dynamics to estimate the long-term impact of management on soil phosphorus accumulation and decline. We validated the model with data from dozens of published studies in the literature for P loss in runoff from cultivated and grazing systems, and for soil P dynamics. In this presentation, we briefly present the model and its validation results, and then show how it can be used to rapidly quantify the impact of agricultural systems on phosphorus loss and the ability of management practices to reduce that loss. Examples focus on phosphorus loss in systems that try to balance both nitrogen and phosphorus management. Our discussion also focuses on model development in general and the need to develop process-based models that are also user-friendly and use readily available input data, especially in the context of simultaneously managing nitrogen and phosphorus.