Careful management and the right technology help protect groundwater from excessive nitrate contamination. Center pivots are a key part of that equation, a University of Nebraska scientist said.

A six-year Institute of Agriculture and Natural Resources study found that nitrate-nitrogen levels in shallow groundwater are lower under center pivot than sprinkler-irrigated fields.

Researchers concluded that irrigating with center pivots instead of furrow systems can significantly reduce shallow groundwater nitrate contamination.

"Compared to conventional furrow and surge irrigation, nitrate-nitrogen contamination in shallow groundwater can be kept consistently at or near 10 parts per million using a center pivot," said Roy Spalding, an IANR hydrochemist who co-led this research.

The U.S. Environmental Protection Agency's safe drinking water standard for nitrates is 10 ppm. About half of Nebraska wells typically exceed that standard, forcing many communities and private well users to treat the contamination or use bottled water.

Nitrate contamination is linked to Blue Baby Syndrome, which lowers the oxygen-carrying capacity of infants' blood, and bladder cancer in middle-aged women.

"The best way to control nitrate leaching to groundwater is to control irrigation water usage and spoon-feed just the right amount of nitrogen fertilizer to crops through a center pivot system," Spalding said, using less water and nitrogen.

Researchers compared irrigation methods in three corn test fields near Shelton, Neb., from spring 1991 through fall 1996 as part of the Management Systems Evaluation Area research project. Groundwater nitrate-nitrogen levels averaged 30 ppm when research began. Nitrate levels generally were highest in the fall, when groundwater levels were lowest, indicating that irrigation water and rainfall flushed much nitrate from the soils to the shallow groundwater.

There were significant climatic differences in the growing seasons during the research, including an unusually wet growing season in 1993 followed by dry seasons in 1994 and 1995. However, shallow groundwater sampling consistently turned up higher average nitrate-nitrogen levels under furrow-and surge-irrigated fields than beneath the center pivot-irrigated field. Nitrate-nitrogen concentrations also fluctuated more widely under furrow irrigation.

"This again suggests that center pivots are vastly superior in applying uniform amounts of water," Spalding said.

After a wet 1993 growing season, shallow nitrate levels dropped about 10 to 15 ppm under the fields. Levels began building up in the 1994 growing season beneath the furrow-irrigated field but remained at about 10 ppm beneath the pivot-irrigated field.

Compared with the furrow-irrigated field, the surge- irrigated field received 60 percent less water and 31 percent less nitrogen, while the center pivot field used 66 percent less water and 37 percent less nitrogen. Although the surge-irrigated field received almost as much water as the center pivot field, it wasn't able to limit nitrate contamination nearly as well, Spalding said.

"The good news is that it's clear that careful management by the producer and innovative agricultural practices can maintain groundwater nitrate concentrations at more acceptable levels without significantly compromising crop yields," he said.

The U.S. Department of Agriculture, Nebraska Research Initiative and Central Platte Natural Resources District helped fund this research.

– Steve Ress