College of Agricultural and Life Sciences

College of Agricultural and Life Sciences

Above ↑ Anita Thompson (center), graduate student Amanda Crowe and research associate Kyunghyun Kim are conducting research on the farm of Bob and Karen Breneman, near Rio, to learn how intensive rotational grazing influences surface water quality.

Does Grazing Influence Surface Water Quality?

Home >> The science of sustainable agriculture >> Does grazing influence surface water quality?

With confinement systems and manure storage, dairy farmers can pick the time and place to spread manure. Grazing cows pick their own time and place, which may not be ideal from a pollution-prevention perspective.

Rotationally grazed cows harvest their own feed during the grazing season, reducing the need to purchase supplemental feed, machinery and other supplies. The animals are “rotated” to new paddocks as needed. About one-quarter of Wisconsin’s 1,250,000 cows get part of their feed ration from pasture, and the percentage of state dairy farms that use grazing is increasing.

In studies on farms in two parts of the state, biological systems engineer Anita Thompson and soil scientist Fred Madison are studying how rotational grazing influences surface water quality. They’ve had instruments on the Bob and Karen Breneman farm, near Rio in south-central Wisconsin, since March 2005. They began a study at the Karl Klessig Saxon Homestead Farm in Manitowoc County in summer 2005.

Thompson and Madison are focusing on overwintering areas, where cattle are kept during the nongrazing months. These areas accumulate livestock waste during the winter, when the cows aren’t being rotated among pastures. The researchers plan to measure snowmelt and rainstorm runoff and determine the sediment, nitrogen and phosphorus loads coming off these areas.

Early results from the Breneman farm showed that phosphorus levels were fairly constant, and fairly low, in snowmelt runoff. The first rainfall after the snow melted produced much higher phosphorus levels in runoff, probably because more sediment was able to move across the bare ground, Thompson reasons. Once the field’s vegetation re-established itself, phosphorus levels dropped off again. She says that 2006 will be the big data collection year at both farms.

Thompson did soil surveys of the farms right after snowmelt to establish the spatial distribution of phosphorus at each site. She hopes to repeat the surveys at the end of the grazing season to see if the distribution has changed. The farms are on different soil types — the Breneman farm on sandy soils, the Klessig farm on red clay — which might give the researchers an indication of the role soil type plays in runoff from rotationally grazed operations.

Hoping to improve nutrient-management planning for grazing systems, researchers from UW-River Falls are studying nutrient flows on several Wisconsin farms that use a management-intensive rotational grazing system, including the Breneman farm.

“These ongoing studies, in addition to our work, will help establish nutrient and contaminant flow paths in grazing systems and help us understand the impacts of these farming systems on surface and groundwater resources,” Thompson says.

This research is funded by the Center for Integrated Agricultural Systems and the Wisconsin Department of Agriculture, Trade and Consumer Protection’s Grazing Lands Conservation Initiative. Agronomist Dan Undersander provided additional support through the Grazing Lands Conservation Initiative.