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
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,"
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
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
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
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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