High levels of nitrate, which pose health threats, occur in shallow ground water in some areas where dryland farming is common. In these areas, the breakdown of crop stubble is a likely source of nitrate. Where wells are located near barnyards and feedlots, livestock wastes are a likely source. A case study in northeastern Montana defined the extent and sources of nitrate in ground water, and determined that changes in land use may affect nitrate levels in ground water, and determined that changes in land use may affect nitrate levels in ground water in less than 30 years. Reductions in nitrate concentrations probably could be achieved through a variety of land-management strategies.