Pasture stocking density ranged from three cows per acre in spring to .5 cows per acre in mid-September during a year with normal rainfall in south-central Wisconsin. Scientists at the U.S. Dairy Forage Research Center and UW-Madison”s College of Agricultural and Life Sciences studied mixed-species pastures, dominated by cool-season grasses.
“There is a misconception that natural pasture is limited to bluegrass when managing for grazing,” said center agronomist Rao Kanneganti. These pastures contained Kentucky bluegrass, smooth bromegrass, quackgrass, and white clover. The ”natural” or permanent pastures, on 36 acres of silt loam soils near Prairie Du Sac, Wis., have not been planted or tilled for more than 10 years.
In 1994 and 1995, pastures yielded 3.5 tons per acre per year of consumable dry matter. Forage consumed from the pasture averaged 22 percent crude protein, 45 percent neutral detergent fiber and 24 percent acid detergent fiber.
The amount of forage available varied from season to season. In 1994, from May 1 to June 1, an average of 68 pounds of forage per acre were available per day; from June 1 to Aug. 15, 59 pounds per acre were available per day; and from Aug. 15 to Sept. 15, 34 pounds per acre per day. From Sept. 15 to Oct. 15 forage availability further decreased to about 12 pounds per acre per day. Rainfall was normal in 1994.
In a dry year, such as 1995, forage availability declines more rapidly and shortens the grazing season. In 1995 there were 70 pounds of forage available per day from May 1 to June 1; from June 1 to Aug. 15, 41 pounds per acre per day; and from Aug. 15 to Sept. 15, 25 pounds per acre per day. Due to drought and an end to grazing, no data were available for Sept. 15 to Oct. 15.
“Farmers can use these data as a guide,” said Kanneganti. During the spring flush farmers can graze three cows per acre, at a feeding rate of 20 pounds of forage dry matter per cow per day. This stocking density would need to decrease to 1.5 cows per acre per day in mid-August and to .5 cows per acre per day in mid-September during a normal year. “Depending on the stocking density, farmers would need to hay the excess forage in the spring or supplement feed later in the season,” Kanneganti said.
Kanneganti also studied species composition in the pastures. Averaged over two years, pasture forage was composed of 22 percent Kentucky bluegrass, 33 percent all other grasses (mostly smooth bromegrass and quackgrass), 13 percent legumes (mostly white clover), 27 percent dead matter, and 5 percent all other species, such as dandelion.
This species composition did not vary during the two-year study, except during the drought from August to September of 1995, said Kanneganti. Dead matter in the pasture increased to more than 50 percent as grass and legume productivity declined. “It is important to watch the pasture and stocking density during periods of drought and make sure the animal is not forced to eat dead matter,” said Kanneganti.
Kentucky bluegrass and white clover suffered the most under the drought stress. However, both recovered to their original percentages as favorable moisture conditions returned, said Kanneganti.
“Mixed species pastures seem to have some buffering against drought effects,” he said. “Clearly they can be quite productive under managed rotational grazing.”
Currently, Kanneganti is studying frost seeding as a method of increasing legume content in managed rotationally grazed pasture.
The pasture research is a part of an ongoing study evaluating low-input pasture and the addition of nitrogen to the environment by managed rotational grazing. Kanneganti will also use the data to test the pasture-analysis components of DAFOSYM, the dairy farm analysis computer program developed by the U.S. Department of Agriculture.