Farmland values are tumbling in California’s Central Valley, reflecting a drop in key commodity prices as well as concerns over water shortages and the state’s enduring drought.

A study released Wednesday by agricultural lender Rabobank N.A. says the price of farmland in parts of the valley will decline by as much as 30 percent between now and the end of 2017, following several years of substantial gains. The drop follows declines in the prices farmers are getting for important crops such as almonds and walnuts.