A representative set of APEX (Agricultural Policy/Environmental eXtender) model runs from across the U.S. will be used for statistical analysis to determine which parameters have the most influence on crop yields, runoff/water yield, erosion, nutrient and pesticide losses, and soil carbon change. The analysis is based on global sensitivity analyses. The analysis will be used for the development of protocol for regional parameterization of simulation models to account for diversity across the United States, calibrating and validating APEX model for national assessment.