DES MOINES -- Farmland values in Iowa have risen about 14 percent in the last year, according to Iowa State University's annual farmland value survey.

The survey, released Tuesday, shows values rising for the ninth year in a row, with the average now at $4,468 per acre.

The 2008 average price was an increase of $560 over 2007, the second-highest dollar increase ISU's survey has recorded.

ISU Extension farm economist Mike Duffy, who conducted the survey, said indicators toward the end of the year show that the upward trend may be slowing as the national economy struggles and commodity prices drop while farm costs rise.

"There have been considerable changes in the situation in Iowa over the past few months," he said in a statement. "Monthly average corn and soybean prices in Iowa had been continually rising until July 2008. Corn averaged $5.41 per bushel in July, and current prices are below $3. Soybeans averaged $13.10 in July, and the current prices are below $8.00 per bushel."

Duffy said the change in revenue had been accompanied by a substantial increase in the costs of production, including fertilizers for seed. That means the upward tick of farmland prices could be slowing, he said.

Lower grain prices in recent months coupled with higher production costs will also mean a lower net revenue per acre, Duffy said.

Duffy said that overall the survey showed strength in farmland value.

He said land values have almost doubled since 2003, when farmland was selling for about $2,275 per acre.

The priciest farmland was in Scott County, in eastern Iowa, where land average $6,310 per acre.

As a region, the state's northwest had the highest farmland values, with an average price of $5,395 per acre.