The average value of a good acre of Iowa farmland declined 7.6 percent to $9,924 over the past six months, according to a survey released Tuesday by the Iowa Chapter of Realtors Land Institute.Combining the 7.6 percent decrease with the 3.4 percent decline reported in September indicates a statewide average decline of 11 percent from March 1, 2014, to March 1 of this year.All nine crop reporting districts posted decreases over the past six months, according to the survey.