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Rige-Tillage System On Sandy Soil Reduces Ground Water Pollution

Compared with conventional moldboard plowing and no-tillage, a ridge-tillage system for corn approximately halved the fertilizer and herbicide movement to ground water while producing comparable yields in a four-year study on a sandy Wisconsin soil.

University of Wisconsin-Madison soil scientist Ronald Hartwig reported on the study Thursday, May 1, at the North Central Section meeting of the Geological Society of America in Madison. Hartwig”s co-authors are Birl Lowery, Kevin McSweeney and Kevin Fermanich. Hartwig, Lowery and McSweeney are in the Department of Soil Science at the UW-Madison College of Agricultural and Life Sciences. Formerly with the department, Fermanich is now with the UW”s Sea Grant Institute.

The researchers evaluated the tillage systems and several irrigation methods at a site near Arena in the Lower Wisconsin River Valley. Farmers there grow seed corn, field corn, sweet corn, snap beans, carrots and potatoes on irrigated sand flats along the valley bottom. In the late 1980s, a state monitoring program found unacceptable levels of nitrates and atrazine, a common corn herbicide, in about half the wells tested there. In 1992, the Wisconsin Department of Agriculture, Trade and Consumer Protection declared a moratorium on atrazine use within the entire 25,000-acre region.

The site”s soil, a Sparta sand, is clearly the most difficult Wisconsin soil in which to control nitrate and herbicide movement, according to Lowery. The soil has a very limited water-holding capacity and is extremely low in clay and organic matter the soil components to which most fertilizer and herbicides bind. The soil also overlies a shallow ground water table.

Lowery and McSweeney have studied the problem since 1989. They adapted a ridge-tillage method that reduces the application rate of atrazine by two-thirds, compared with the herbicide rate applied to the other two systems. The ridge-tillage system employed as much nitrogen fertilizer as the no-tillage and moldboard-plow systems, in which the fertilizer is broadcast over the field surface. But in the ridge-tillage system, the fertilizer is banded along the ridges.

Placing chemicals on and in the ridges and timing applications to the crop”s growth cycle significantly reduced the amount that moves to ground water. The corn in the ridge-tillage system produced an average of 151 bushels per acre compared with 135 for no-tillage and 152 for moldboard plow tillage.

The researchers found that not irrigating the moldboard-plow system and no-tillage system reduced the movement of the chemicals to ground water even more than in the irrigated ridge-tillage system. However, it also reduced corn yields by about 50 percent.