Percent change in the average annual Producer Price Index (PPI) for corn, soybeans, and wheat, 1973-74, 1988, 1996 Corn Soybeans Wheat 1973 70.8 103.6 96.8 1974 44.0 -4.7 33.3 1988 43.4 41.3 28.7 1996 45.4 25.1 15.2