Proper N management for agricultural production is critical to minimize groundwater contamination with NO 3. For 18 yr, research was conducted to observe NO 3-N concentrations in the vadose zone, groundwater, and subsurface drainage under sprinkler-irrigated, primarily corn ( Zea mays L.) production. Potato ( Solanum tuberosum L.) and soybean [ Glycine max (L.) Merr.] were also grown intermittently on the site. The lysimeter leachate NO 3-N concentration increased to 156 mg L -1 under corn production within 1 yr after the initiation of irrigation (at the onset of the study), then decreased to
