When manure, or other nutrient-rich materials are added to the soil, nitrogen is the nutrient usually used to determine the application rate. Phosphorous is another nutrient in manure which can impact the environment when applied in excess. Fortunately, phosphorous is relatively immobile in the soil. However if applied to excess year after year, then there is a chance for it to become an environmental problem as runoff and erosion carries it to ponds and streams. This project is designed to establish acceptable P levels on farm land and determine how it behaves under various soil and moisture conditions by developing a model that simulates various field and soil conditions and follows the movement of P through plant uptake under different field profiles and rainfall situations. The Nutrient Loading Model (NLM) accomplishes this in both a forward or “predictive” sense and in a reverse or “regulatory” sense. In the predictive mode, it predicts the level of P in streams that results from nutrient applications to the soil. In the reverse mode, it starts with the P concentration in the water that would be considered acceptable and establishes the amount of P that could be added to the soil to not exceed this downstream water concentration. Once the model is tested and gains acceptance from those involved in watershed studies of soil erosion, it will be a valuable tool for resource protection agencies and livestock manure managers.