Beginning in 1981, a mathematical model called the erosion-productivity impact calculator model (EPIC) was developed to determine the relation between soil erosion and soil productivity throughout the U.S.A. By 1985 the model was ready for use in the RCA (1977 Soil and Water Resources Conservation Act) analysis. Between 15 000 and 20 000 EPIC simulations of 100 years each were performed as part of the 1985 RCA analysis. After the RCA analysis, model refinement and development continued and EPIC has been applied to a number of agricultural management problems. For example, EPIC is capable of dealing with decisions involving drainage, irrigation, water yield, erosion (wind and water), weather, fertilizer and lime application, pest control, planting dates, tillage, and crop residue management. Example applications include: (i) 1988 drought assessment; (ii) soil loss tolerance tool; (iii) Australian sugarcane model (AUSCANE); (iv) pine tree growth simulator; (v) global climate change analysis, and (vi) farm level planning.