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Sustainable Agriculture

Grass-Based Dairy Systems Prove a Water Quality Winner

Pasture-based dairy farmers report increased profits, a more relaxed lifestyle, and a host of environmental benefits not found in systems that require rearing field crops for animal feed and confining cows in barns. Sustainable Agriculture Research and Education (SARE)-funded research at the University of Wisconsin bears out at least one of those claims: management-intensive grazing (MIG) is better for groundwater quality than conventional dairy/crop farms.

Scientists often attribute groundwater contamination in central Wisconsin to nitrates from agricultural practices, but SARE-funded research on two grass-based dairy farms in the area showed that grazing did not affect groundwater seriously.

Researchers Nancy Turyk, Michael Russelle, and Bryant Browne launched a study to determine if denitrification might be responsible for protecting the groundwater. The study is taking place on three MIG farms and a conventionally cropped dairy farm in three central Wisconsin counties.

In a typical crop farm, nitrogen—most often applied as commercial fertilizer—is converted into nitrates that move through the soil profile and can pollute groundwater and nearby streams and rivers. Preliminary results from the Wisconsin grazing systems study show that some of the nitrogen on MIG farms is changed into nitrogen gas released into the atmosphere as a benign component of air.

Other studies suggest that the denitrification occurs thanks to higher levels of bacteria in grassland soils. Moreover, the researchers attribute the greater gas conversion to bacterial food from animal waste.

“Denitrification occurs more readily with animals on the grassland because they add more carbon and bacteria to the system,” Turyk said. Moreover, the dense and deep root systems formed by the roots of perennial grasses and legumes can absorb excess nitrogen, in stark contrast to most annual crops.

“In crop farms, farmers usually fertilize at planting when there are no roots to capture excess nitrogen,” Turyk said.

Wisconsin dairy farmers are interested in the findings. Four of them volunteered to help monitor their herd movements in and out of pasture paddocks. Paul Onan of Portage County converted his 50-cow herd to grass-based dairying in 1994 and was eager to learn if his aim to be more environmentally friendly was paying off.

“We're still adding nitrates to the groundwater, but not nearly as much as under a cropping situation,” Onan said. “We need to try to fine-tune our system.”


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