Assessments of Soil Erosion and Crop Productivity with Process Models (EPIC)

Accurate estimates of future soil productivity are essential in agricul tural decision making and planning from the field scale to the national level. Soil erosion depletes soil productivity, but the relationship between erosion and productivity is not well defined. Until the relationship is adequately de veloped, selecting management strategies that maximize long-term crop production will be impossible. The Soil and Water Resources Conservation Act of 1977 (RCA) re quires a report by 1985 that establishes the current status of soil and water resources in the USA. One important aspect of these resources is the effect of erosion on long-term soil productivity. The National Soil Erosion—Soil Productivity Research Planning Committee documented what is known about the problem, identified what additional knowledge is needed, and outlined a research approach for solving the problem (Williams et al., 1981). One of the most urgent and important needs outlined in the research approach was the development of a mathematical model for simulating ero sion, crop production, and related processes. This model will be used to de termine the relationship between erosion and productivity for the USA. Thus, a national ARS erosion-productivity modeling team was organized and began developing the model during 1981. This team consisted of J. R.