Iowa losing its topsoil at greater rate than previously thought

Water runs off a Buchanan County farm field, carrying away soil and deepening a gully in a drainage area unprotected by
Water runs off a Buchanan County farm field, carrying away soil and deepening a gully in a drainage area unprotected by a grass waterway during a rain shower on Tuesday, April 19, 2011. (Orlan Love/SourceMedia Group News)

Iowa is losing much more of its precious topsoil than previously thought, according to a study based on data collected by Iowa State University scientists.

The recent surge in erosion has been driven by an increase in extreme rainstorms, insufficient enforcement of conservation requirements and farmers’ maximization of plantings in an era of high commodity prices, scientists and environmentalists say.

Iowans have gotten a false sense of security from U.S. Department of Agriculture estimates that annual statewide soil losses average barely more than the acceptable rate of 5 tons per acre.

Research by ISU scientists shows erosion in some parts of the state as much as 12 times higher than the tolerable rate, with the heaviest losses in southwest and southeast Iowa.

“Soil erosion in Iowa is getting much worse because of the increased frequency of extreme rainfall,” said Richard Cruse, an ISU agronomy professor who directs the Iowa Daily Erosion Project.

Unlike the USDA estimates, which are statewide averages based on average rainfall over the past 25 years, the ISU project focuses on individual rain storms at the township level.

“Averages don’t tell you what is really happening. They mask really large rainfall events and cover up serious erosion in localized areas,” Cruse said.

While an inch of rain over 24 hours is usually welcome, “when you get an inch in 15 minutes, all hell breaks loose,” he said.

“We are conservation planning for averages, not extremes, but nature doesn’t seem to work that way,” said Decorah farmer Paul Johnson, a former chief of the USDA’s Natural Resources Conservation Service and former director of the Iowa Department of Natural Resources.

The Iowa Farm Bureau Federation hailed the ISU project’s quantification of erosion “as a significant step forward.”

The Iowa Corn Growers Association said the heightened erosion identified by the ISU researchers reflects recent rainfall surges rather than any slackening of conservation ardor.

“Too much water, like we have been getting in recent years, damages any soil and cannot be prevented,” said Jay Lynch, a Humboldt farmer who chairs the association’s animal and environment committee.

Lynch, 31, recalls a recent downpour of 2 inches in 40 minutes on his own farm. “You did everything you could, but it made a gully. It’s hard to look at, but it’s a fact of life,” he said.

Clear Lake area farmer Chris Petersen, president of the 1,400-member Iowa Farmers Union, shares Lynch’s sick feeling at watching a heavy rain erode his soil’s productivity, but he believes farmers could do more to prevent erosion.

“We’re farming anything and everything for $7 corn,” he said, including frequent encroachments on grass waterways and other soil conservation structures.

While no one has an accurate record of waterways and buffer strips converted to row crop production, “folks are telling us it’s happening,” said Craig Cox of Ames, a senior vice president of the Environmental Working Group, which analyzed the ISU data and issued a report titled “Losing Ground” last week.

Cox said the federal agency responsible for enforcing compliance with conservation provisions of the 1985 Food Security Act, which predicated federal farm subsidies on adoption of conservation practices on vulnerable farmland, has been lax in doing so.

He cited a 2003 Government Accountability Office report that stated that almost half the Natural Resources Conservation Service field offices “do not implement the conservation provisions as required because they lack staff, management does not emphasize those provisions or they are uncomfortable with the enforcement role.”

With 23 million Iowa acres under row crop production, “there have to be some cases” of farmers encroaching upon grass waterways and buffer strips, said Bill Northey, secretary of the Iowa Department of Agriculture and Land Stewardship.Based on the demand for cost-share assistance for new conservation projects, however, Northey said most farmers want to practice more soil conservation, not less.

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