The hydrologic component consists of two options. When only daily rainfall data are available to the user, the SCS curve number model is used to estimate surface runoff. If hourly or breakpoint rainfall data are available, an infiltration-based model is used to simulate runoff. Water movement through the soil profile is modeled using a simple capacity approach, with flow occurring when a layer exceeds field capacity. The erosion component maintains elements of the USLE, but includes sediment transport capacity for overland flow.
Plant uptake is estimated, and nitrate leached by percolation out of the root zone is calculated.
Furthermore, both the nitrogen and phosphorus parts of the nutrient component use enrichment ratios to estimate that portion of the two nutrients transported with sediment. The pesticide component considers foliar interception, degradation, and washoff, as well as adsorption, desorption, and degradation in the soil. References Foster, G. R., L. J. Lane, J. D. Nowlin, J. M. Laflen and R. A. Young. A field scale model for Chemicals, Runoff, and Erosion from Agricultural Management Systems, U. S. Dept. of Agric. Sci. and Educ.