Studies were made in 1954, 1955, and 1956 of the effects of various quantities of normal sunlight, obtained by the use of shade structures, on growth and grain production of three corn hybrids: Illinois 972A, Hy2 ✕ Oh41 (tolerant of high rates of planting), and WF9 ✕ C103 (intolerant of high rates of planting). The light treatlnents in 1954 were 100% (control), 70, 40, and 10%; 1955 and 1956, additional treatments of 30 and 20% were used. Shading was initiated in 1954, 1955, and 1956 on July 2, July 5, and June 8 thus providing 90, 72, and 113 days of treatment, respectively.In general, there was a significant decrease in measured components (grain, stover, total protein, total oil, etc.) as light was decreased. With minor exceptions, e.g., height, reduction of light by even 30% caused a decrease in production of plant material. Of signal importance is the essentially linear reduction in total plant (grain and stover) protein with decrease in light.Based on grain yields, Hy2 ✕ Oh41 proved to be more tolerant of low light levels than did WF9 ✕ C103 when shade treatments were imposed in mid‐season at a time when mutual shading becomes intense in dense plant populations.
