U.S. Water News Online
LINCOLN, Neb. -- Irrigating with sprinkler instead of furrow irrigation systems can reduce shallow groundwater nitrate contamination, University of Nebraska research shows.
Results from a six-year study of irrigation systems on three corn test fields near Shelton, Neb., leave little doubt that if more center pivot sprinklers were used to irrigate crops, groundwater nitrate contamination could be significantly reduced, said Roy Spalding, an NU hydrochemist and co-leader of this research.
"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," the NU Institute of Agriculture and Natural Resources researcher said.
The U.S. Environmental Protection Agency's safe drinking water standard for nitrates is 10 ppm. Much of Nebraska's shallow groundwater exceeds that standard, which forces many communities and private water well users to treat the contamination or use bottled water, he said.
Nitrate contamination has been linked to health risks such as Blue Baby Syndrome, which lowers oxygen-carrying capacity of infants' blood, and bladder cancer in middle-aged women.
"The best way to control nitrate leaching to the groundwater is to control irrigation water usage and to spoon-feed just the right amount of nitrogen fertilizer to crops through a sprinkler system," Spalding said.
He and fellow NU researchers came to that conclusion after six years of controlled testing of gravity-type furrow and surge irrigation and sprinkler-type center pivots. Studies were conducted in three adjoining, 40-acre corn plots at the university's Nebraska Management System Evaluation Area near Shelton from spring 1991 to fall 1996.
Irrigation methods and fertilizer management techniques on the test fields were closely monitored using more than 30 multi-level sampling wells. These wells allowed researchers to analyze water samples from as many as 16 different depths throughout the underlying aquifer.
When research began, samples showed nitrate-nitrogen levels averaging 30 ppm, three times the EPA's safe drinking water limit. Nitrate levels were generally highest in the fall, when groundwater levels were the lowest, indicating that irrigation water and rainfall had flushed much of the nitrate from the soils to the shallow groundwater.
There were significant climatic differences in each of the growing seasons during the research, including an unusually wet season in 1993 followed by dry seasons in 1994 and 1995. However, shallow groundwater sampling consistently found higher average nitrate-nitrogen levels under furrow- and surge-irrigated fields than beneath the center pivot-irrigated field.
"There also were larger fluctuations in the nitrate-nitrogen concentrations associated with the furrow irrigation method. This again suggests that center pivots are vastly superior in applying uniform amounts of water," Spalding said.
After the 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 sprinkler-irrigated field.
Researchers carefully monitored the amounts of nitrogen fertilizer and irrigation water applied to the fields. Compared to the furrow-irrigated field, the surge-irrigated field received 60 percent less water and 31 percent less nitrogen, while the center pivot field got 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.
"With a center pivot, the producer can uniformly apply water and nitrogen at optimum times for crop uptake, thereby using substantially less water and nitrogen," he 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," Spalding said.
Center pivot is the primary irrigation system used in Nebraska, accounting for more than 4.6 million of the state's more than 7 million acres of irrigated cropland, according to an NU agricultural economist's recent inventory of Nebraska's irrigated acres.
The research findings were published in the July-August edition of the Journal of Environmental Quality.
This research, conducted in cooperation with IANR's Agricultural Research Division, was funded in part by the U.S. Department of Agriculture, the Nebraska Research Initiative and the Central Platte Natural Resources District.
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