USDA-Natural Resources Conservation Service is partnering with Agricultural Research Service (ARS), the National Agricultural Statistics Service (NASS), Farm Service Agency (FSA) and other agencies to conduct a national assessment of environmental benefits and effects of 2002 Farm Bill programs. The resulting Conservation Effects Assessment Project (CEAP) has two components; one of which is a national-scale assessment effort using the National Resources Inventory (NRI) as a sampling base for estimating the environmental benefits of the implementation of conservation practices. The Agricultural Policy Environmental Extender (APEX) model has been proposed for use to evaluate on-site benefits of conservation practices in place in cultivated croplands. Farmer surveys have been conducted at a subset of NRI sample points about ongoing farming activities and conservation practices; and an array of databases has been generated and utilized to provide base data to simulation models. An independent evaluation of the cropland component of the national-scale assessment is being performed at the USDA-ARS Crop Systems and Global Change Laboratory and the University of Maryland. Objectives, evaluation approach, tools used as well as preliminary results are shown in this presentation.