Corn yields of more than 200 bushels per acre were produced on three subplots during 1982. The highest corn yield that year was 215 bushels on the subplot which had received LNPK 1955 to present, but previously had received no limestone or fertilizer treatment. During 1985, this same subplot produced 205 bushels of corn per acre. Soybeans, now the second most important crop in Illinois but unknown in the state when the plots began, were introduced into the cropping system in 1968 as part of a corn-soybeans rotation. With limestone and fertilizer added, soybean yields have increased to 48 bushels an acre.
Organic matter has favorable effects on soil productivity.
Good soil management for high crop yields increases the amount of crop residue returned to the soil. Crop yields have been influenced by both soil treatment and cropping systems. From the story of the Morrow Plots comes both a warning and a promise. The warning is symbolized by the top ear of corn in Fig. 1. This ear grew on a plot whose soil was once productive.