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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