Far More Nitrogen Leached From Corn Fields Than A Nearby Restored Prairie
The amount of nitrogen that leached from two corn fields during a three-year study was many times greater than that leaching from a restored prairie, according to University of Wisconsin-Madison scientists.
Researchers from the College of Agricultural and Life Sciences found that nitrogen leaching from no-till and chisel-plow corn ranged from 32 pounds to 80 pounds per acre per year during the study. “More than half the annual total of 80 pounds of nitrogen leached during a heavy June rainstorm,” says John Norman, a soil physicist who led the research team. “By comparison, only about a pound of nitrogen per acre per year leached from the prairie.”
“We are not suggesting that farmers plant prairie instead of corn,” says Larry Bundy, a soils extension specialist. “The study looked at two systems on the same soil type. One is the current vegetation, corn, an annual plant that requires the highest nitrogen input of any Wisconsin crop. The other is the historic vegetation cover, prairie with perennial plants that receive no fertilizer. The restored prairie gives us a reference point for evaluating current systems.
“This is the first step in understanding the broad picture of nitrogen movement in these systems. Next, we need to evaluate ways to minimize the losses,” Bundy says.
In addition to Norman and Bundy, the research team included soil science graduate student Kris Brye and forest ecologist Tom Gower. The researchers are publishing the first of their findings in the April-May issue of the Soil Science Society of America Journal.
The study was conducted on a deep prairie soil about 20 miles north of Madison, Wis. The two corn sites are located at the College”s Arlington Agricultural Research Station. The restored prairie is a mile away at Madison Audubon Society”s Goose Pond Wildlife Sanctuary. The sites share a common soil type and had a similar farming history until the prairie was re-established.
The researchers estimate that total nitrogen input to the corn fields ranged from 250 pounds to 300 pounds per acre per year, while the prairie received 70 to 75 pounds of nitrogen per acre per year. The corn received 160 pounds of nitrogen per acre as ammonium nitrate at planting, usually the first week of May. The prairie received nitrogen only from rain and decaying plant matter.
Nitrogen travels in water as nitrate and nitrite. Much of the water and nitrogen that move below the root zone will eventually reach ground water, the drinking water source for most rural Wisconsin residents. High levels of nitrogen in ground water have been linked to “blue-babies,” an oxygen-deficiency problem in babies” blood that can result in injuries and even death. The federal and state drinking water standard for nitrogen is 10 parts per million. Studies show that wells in many southern Wisconsin counties already exceed the standard, according to Norman.
The study used state-of-the-art methods to monitor water and nitrogen movement in undisturbed soils throughout the year. In fact most of the water that percolated through the sites did so between January and June, according to Brye. [see here for details.]
The study didn”t evaluate how nitrogen rates or timing would affect leaching, according to Bundy. “It seems reasonable that fall-applied nitrogen would be at particular risk for loss given the timing of the leaching we observed,” he says.
Bundy also noted that the 1995 to 1998 period included some unusual storms.
In June 1996, for example, there was a 4 1/2-inch rainstorm that caused one corn site to lose more than 50 pounds of nitrogen per acre to leaching in just two days, Brye says. A 1 1/8-inch rain and thaw that occurred during January 1996 flushed 6 and 8 pounds of nitrogen per acre from below the two corn fields even though the soil was frozen.
“In the past, scientists measured leaching during the growing season, but seldom found any losses,” Norman says. “If ground water contamination is occurring at our Arlington sites, it”s happening mainly between January and June, not during summer or fall.”
The research was supported by state funding to the UW-Madison College of Agricultural and Life Sciences and a USDA Hatch grant from the College of Agricultural and Life Sciences. The scientists had been unable to find support to expand the research. However, the Wisconsin Department of Natural Resources and the Wisconsin Fertilizer Research Fund have agreed to support an additional two years of monitoring at the sites.