Discretionary environmental provisions could add to the Conservation Reserve Program's (CRP) objectives but would complicate the program. Nationally consistent criteria for designating fields contributing to salinity and selenium pollution, groundwater declines, loss of wetland habitat, or groundwater pollution are not yet available. Particularly vexing for the CRP would be groundwater problems, since the main cropland contributors generally have not yet been identified, and such croplands may be widely dispersed. In spite of these challenges, enrollment of marginal acres contributing to several environmental problems offers economic advantages, especially if States take action to foster enrollment in watersheds actually subject to pollution.