In response to surging Midwest farmland prices, researchers in Iowa are overhauling a decades-old formula used to predict corn yields, which will allow farmers and tax officials to more accurately value property.

The corn suitability rating, or CSR, has long been a Midwestern benchmark to forecast how productive an Iowa farm will be if corn is planted on it.

Since 1971, CSR has been used to set cash-rent rates, help farmers gauge how much to spend on fertilizer and other inputs, and figure out how agricultural land is valued for property tax purposes.