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A Restored Prairie Gets Less Water But Holds More Than Nearby Corn Fields

The soil under a restored prairie in southern Wisconsin received much less moisture but retained more of it than two nearby corn fields, according to University of Wisconsin-Madison research.

The three-year study is the first in the nation to monitor water movement in undisturbed soils below corn fields and a prairie throughout the year.

The differences in water movement between the soil below a 20 year-old prairie, and that below corn planted into no-till and chisel-plow fields surprised researchers at the College of Agricultural and Life Sciences. Their results provide new insights into how agriculture changed the soil below prairies, which were common in southern Wisconsin before settlers began farming in the mid-1800s.

“Although the precipitation at the sites was basically the same, soil below the prairie received only about two-thirds as much water as did soil below the corn fields. That”s a big difference,” says John Norman, a soil physicist who led the research team.

The team includes soil science graduate student Kris Brye, soils extension specialist Larry Bundy, 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 thatch and dead grass on the prairie surface intercepts much of the water before it reaches the soil,” Brye says. “That water evaporates back into the air.”

“Although soil below the prairie typically received less water, we found that it held almost 10 percent more water than soil below the corn fields,” says Norman, “even though the soils had the same texture and organic matter. Roughly two to three times more water drained from below the root zone of the corn fields than the root zone of the prairie.”

“When the prairie burned one spring destroying the thatch layer, the amount of water percolating below its root zone more than doubled,” Brye says.

The researchers aren”t certain why water moves more readily through the soil below corn. Norman suspects it may move down through root channels left by earlier corn crops.

The study was conducted on a deep prairie soil near Arlington, Wis., about 20 miles north of Madison. The corn sites are in adjoining fields and the prairie site is a mile away. The sites shared a common soil type and a similar history until the prairie was re-established.

The researchers measured water as precipitation, run off, soil storage, and drainage; they determined water lost from the soil surface and vegetation by difference. The new lysimeters they developed and installed 4 1/2 feet below the sites allowed them to measure water draining from the root zone year-round. The measurement is extremely accurate because the method continually adjusts the lysimeter to match the conditions in soil a few inches away.

Using the new methods, the researchers found that a winter rain drained right through part of a corn field where the soil was frozen 20 inches thick, Norman says. In fact, most of the water that percolated through two corn fields did so between January and June.

“We”re used to thinking of winter as a dormant season when nothing much is happening, but we”re learning otherwise,” says Norman.

Norman has a theory about how winter rains can move through frozen soil. He believes that if soils are moist, freeze rapidly and stay frozen, they contain pores that function like open pipes conducting water down. But if an area freezes slowly, as it does when there is snow cover, or if the soil thaws and refreezes a few times, there are no pores to conduct water.

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.