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Intensifying Plant Density Response of Corn with Artificial Shade

College of Agric., Shahid Chamran Univ., Ahwaz, Iran
Dep. of Plant and Soil Sci., Univ. of Massachusetts, Amherst, MA 01003

^* Corresponding author.

Competition among corn (Zea mays L.) plants for interception of photosynthetically active radiation (PAR) at high plant density can result in a reduction in kernel number per ear and complete ear barrenness. The response of field corn to long-term shading as density increased was investigated. A single-ear hybrid was grown at the Agricultural Experiment Station Farm, Univ. of Massachusetts, at three densities of 3,7.5, and 12 plants m^–2. Shading was provided by using black polypropylene fabric with 50% light penetration installed 44 d after emergence. The rate of apparent photosynthesis in ear leaves was reduced significantly by both increased plant density and shading. The reduction was attributed to reduced PAR in higher densities and shaded plots and to the decreased chlorophyll concentration measured in leaves of plants at high density in both ambient light and shaded plots. Tassel emeqence was slightly delayed in high density and shaded plots. However, the time of silking was delayed significantly because of both high density and shading. Seven days after anthesis, 10% of plants in high densities and 50% of plants in shaded plots had no silk. The response of grain yield per unit area in ambient light to increasing density was parabolic. No increase in yield was obtained with density increase in the shaded plots. Shade reduced the number of productive ears per plant, and the number of kernels per row resulting in a 23 and 66% yield reduction in low and high plant densities respectively, when compared to ambient light. Weight per kernel was reduced 28% with increased plant density. Shading did not further decrease kernel weight. The number of kernel rows per ear was least sensitive to both high plant density and shading.

Received for publication May 29, 1991.

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