Long-Term Observations of Vadose Zone and Groundwater Nitrate Concentrations under Irrigated Agriculture

Proper N management for agricultural production is critical to minimize groundwater contamination with NO3. For 18 yr, research was conducted to observe NO3-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 NO3-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