Minnesota farmland values have kept rising this year at a double digit rate, but the pace slowed as grain prices have softened.

The state's cropland is worth $4,870 per acre on average in 2014, up 11 percent over a year ago, according to fresh data from the United States Department of Agriculture.

In 2013, cropland value was up 17 percent over the previous year, and it rose 13 percent in each of the years prior to that. In 2010, the average value of Minnesota cropland in 2010 was $2,710 per acre, according to the USDA.

Cropland rental rates fell even further this year, a relief to farmers who must rent acreage. Cash rent on average is $186 per acre this year, up 4.4 percent from a year ago, the USDA says. In each of the previous two years, rental rates jumped 18 percent.

The run-up in the state's farmland mirrors trends across the country as commodity prices rose at robust rates. In 2012, corn was fetching around $7 a bushel.

But with a big corn crop in 2013 – and another one expected this year – prices mostly hovered between $4.50 and just over $5 a bushel from last August through June. In the past month, they've tanked, with the September corn futures contract currently at about $3.55.

Falling prices should put further downward pressure on land values. But in the short term, farmers have a more pressing concern: corn prices so low that they can't cover this season's cost of production.