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Effects of Shade Applied at Different Stages of Plant Development on Corn (Zea mays L.) Production¹

The effects of reducing the amount of sunlight at the vegetative, reproductive, and maturation phases on the morphology, grain yield, and chemical composition was determined for two corn hybrids.

The shade treatments exerted significant reductions inall components measured except those established prior to initiation of treatment. Shading for 21 days during the reproductive phase was more detrimental to grain production per plant than shading for longer periods during vegetative and maturation phases. When shaded at 60, 70, and 80% during the vegetative or reproductive phase, Hy2 x Oh41 produced more grain per plant than WF9 x C103, while the reverse was true during the maturation phase. The hybrids exhibited a differential response to shade treatments only during the vegetative phase. With respect to number of kernels and grain yield, shading during the vegetative phase was more detrimental to WF9 x C103 than Hy2 x Oh41 while the reverse was true during the reproductive phase. During maturation the reduction in grain protein was not proportionally as great as the reduction in grain yield for both hybrids.

Extensive vegetative growth during the first 54 days was not a prerequisite for a high grain yield per plant. These observations provide an explanation for the frequent failure of starter fertilizers to enhance grain yield and suggest management practices that might produce higher yields.

Plants shaded at 60% or higher during the reproductive phase had a full complement of normal leaves, but initiated and developed only a limited number of kernels. Weight per kernel and stover weight per plant at the end of the season were less than that of the control plant. Since these leaves were exposed to full sunlight from August 8 to the end of the season, they must have been essentially nonoperative during this period.

Key Words: shade effects • developmental stages • corn production

² Professor of Plant Physiology, former graduate student (now at Oklahoma State University), Associate Professor of Biometry, and Professor of Plant Physiology, respectively.

Received for publication October 28, 1966.