Integrated irrigation and nitrogen management impacts on ground water quality in Southeastern North Dakota

Research on irrigation water and nitrogen fertility management for corn, soybean, and potato production, and the attendant impacts on ground water quality, has been conducted on two field-scale sites in southeastern North Dakota from 1989 to the present. An irrigated quarter section was instrumented extensively with ground water observation wells in the shallow surficial aquifer, disturbed- and undisturbed-profile drainage lysimeters, and manhole access points along two subsurface drains, Corn was planted at the site from 1989 to 1995 and in 1997 and 1998, with potatoes added to the rotation in 1996 and 1999. A nearby, smaller field site without subsurface drainage has been used for research on irrigated corn and soybean management practices from 1990 to 1995; corn was grown in 1996, 1998, and 1999; and potatoes were grown at the site in 1997. Ground water quality samples have been collected for both sites and analyzed for nitrate-nitrogen (NO3-N) concentrations. Concentrations of NO3-N in the top of the surficial aquifer, as well as in the lysimeters, increased greatly after the onset of irrigation at each site, then decreased to near pre-irrigation levels. Concentrations of NO3-N in the subsurface drains have remained in the 2 to 6 ppm range, with the exception of three events in which concentration spikes were attributed to large recharge events that were depression focused.