Testing soils for nutrients is expected to improve groundwater quality. However, it is unknown whether soil testing will improve groundwater quality sufficiently to decrease the demand for direct regulation of agricultural practices. Focusing on an irrigated agricultural region in eastern Oregon, the economic and environmental aspects of soil testing are assessed using a spatially distributed, dynamic simulation model which links economic behavior with the physical processes that determine groundwater quality. Results indicate that soil testing of all fields increases farm profits and reduced groundwater nitrate concentration. However, the benefits are small in terms of potential improvements in groundwater quality