Historical Development and Applications of the EPIC and APEX models

Abstract

The development of the field-scale Erosion Productivity Impact Calculator (EPIC) modelwas initiated in 1981 to support assessments of soil erosion impacts on soil productivity for soil,climate and cropping conditions representative of a broad spectrum of U.S. agriculturalproduction regions. The first major application of EPIC was a national analysis performed insupport of the 1985 Resources Conservation Act (RCA) assessment. The model has continuouslyevolved since that time and has been applied for a wide range of field, regional, and nationalstudies both in the U.S. and in other countries. The range of EPIC applications has also expandedgreatly over that time including studies of: (1) surface runoff and leaching estimates of nitrogenand phosphorus losses from fertilizer and manure applications, (2) leaching and runoff fromsimulated pesticide applications, (3) soil erosion losses from wind erosion, (4) climate changeimpacts on crop yield and erosion, and (5) soil carbon sequestration assessments. The EPICacronym now stands for Erosion Policy Impact Climate, to reflect the greater diversity ofproblems that the model is currently applied to. The Agricultural Policy EXtender (APEX) model isessentially a multi-field version of EPIC that was developed in the late 1990s to addressenvironmental problems associated with livestock and other agricultural production systems on awhole farm or small watershed basis. The APEX model also continues to evolve and to be utilizedfor a wide variety of environmental assessments. The historical development will be presentedfor both models as well as example applications at several different scales.