A federal report showing a sharp rise in the value of Midwestern farmland last year rings true for Wisconsin farmers and agriculture industry observers, who say high commodity prices are a main factor in a yearslong trend that in some places has doubled or tripled the per-acre price of tillable land.

Farmland values rose 16 percent in 2007 in an area that covers Iowa, Michigan and most of Wisconsin, Illinois and Indiana, according to a survey by the Federal Reserve. It's the biggest one-year increase in almost 30 years.

Prices are "going through the roof," said Ed Kraisinger, a real estate agent who markets farmland in Grant, Iowa, Lafayette and Sauk counties for First Weber Group in Dodgeville.

Whereas prices five years ago were around $1,500 an acre, some farms are now going for as much as $6,000 an acre, he said. According to the U.S. Agriculture Department, the statewide sale price of an acre of farmland went from $2,251 in 2002 to $3,366 in 2006, the last year for which data is available.

Paul Zimmerman, public affairs executive director for the Wisconsin Farm Bureau, said the trend has mainly to do with record prices for commodities such as corn and soybeans, demand for land from people looking to build rural homes and the need among dairy farmers for more land to comply with new state regulations that limit the amount of manure that can be spread over an area.

Ethanol - a biofuel made from corn - isn't a primary factor in the increase in commodity prices and farmland values, he said. Zimmerman said research has shown the demand for ethanol accounts for only a small portion of the price of a bushel of corn, now trading at around $5.50 a bushel. More important is strong demand from developing countries such as China and a weak U.S. dollar, which increases exports, he said.

Of the states surveyed, Wisconsin saw the smallest increase in farmland values in 2007 - 11 percent. Zimmerman speculated that may be partly because Wisconsin is not as affected by high corn prices because it doesn't grow as much corn as other states in the region.

Doug Brown, who raises dairy cattle and grows corn and alfalfa on 400 acres north of Belleville, said he's seen farmland prices go up around his land.

"It's taken a pretty good jump for the last five or six years," he said.

Two years ago, Brown paid $6,000 an acre to buy 80 acres that he had been renting. He said land closer to town - most likely slated for development - can go for $8,000 and $10,000 an acre.

Brown said that as prices have gone up, he's seen the market for sellers soften a bit, but not for landlords.

"It's kind of like a bidding war out here" for farmland to rent, he said. He and other farmers report seeing per-acre rents at $300 or more, when only a few years ago they were half that or less.

It also doesn't mean farmers are reaping big profits. The costs for fertilizer and fuel also have gone up, cutting into farmers' margins.

"There is not a farmer in this area that's going to tell you they're comfortable," said Kraisinger.