Betting the farm on record crop, livestock and dairy prices has turned into a losing investment for an expanding share of America’s agricultural heartland. The level of debt to income is the highest in three decades, and growers are increasingly unable to make loan payments. Four years after record U.S. crop and farmland values boosted purchases of land and equipment, a global surplus has sent prices tumbling and farm income into the longest slump since 1977. The Federal Reserve says growers are borrowing more to pay bills, repayment rates are plunging, and the number of bankers requesting additional collateral is the highest in 25 years.