Slumping crop prices and uncertainty about trade agreements are eroding Iowa farmland values, according to a new Iowa Realtors Land Institute survey.

Average farmland values declined 1.7 percent in the past six months, erasing more than one-half of the 2.9 percent gain in the previous six-month period, said survey coordinator Kyle Hansen of Hertz Real Estate.

“The attitude in the land market has completely changed from a year ago,” said Hansen. “The overall feel is to push the market softer yet. It feels...