Across the U.S. Midwest, the plunge in grain prices to near four-year lows is pitting landowners determined to sustain rental incomes against farmer tenants worried about making rent payments because their revenues are squeezed. On Friday, tractor maker John Deere (DE.N) cut its profit forecast citing falling sales caused by lower farm income and grain prices. Many rent payments – which vary from a few thousand dollars for a tiny farm to millions for a major operation – are due on March 1, just weeks after the U.S.