Corn plants increase in weight slowly early in the growing season. But as more leaves are exposed to sunlight. the rate of dry matter accumulation gradually increases.
The leaves of the plant are produced first, followed by the leaf sheaths, stalk, husks, ear shank. silks, cob and finally the grain. By stage V10, enough leaves are exposed to sunlight so the rate of dry matter accumulation is rapid.
Under favorable conditions, this rapid rate of dry matter accumulation in the above-ground plant parts will continue at a nearly constant daily rate until near maturity (see figure 53).
Cell division in the leaves occurs at the growing tip of the stem. Leaves enlarge, become green. and increase in dry weight as they emerge from the whorl and are exposed to light, but no cell division or enlargement occurs in the leaves after they are exposed. All leaves are full size by V12, but only about half of the leaves are exposed to sunlight.
If a corn plant is grown under low plant density, prolificness may result. Increasing the number of plants in a given area reduces the number of ears per plant and the number of kernels per ear. This reduction is greater for some hybrids than for others. Grain production per hectare (or acre) will increase with an increase in number of plants per hectare until the advantage of more plants per hectare is offset by the reduction in number of kernels per plant. The optimum plant population is different for different hybrids and in different environments.
Highest yields will be obtained only where environmental conditions are favorable at all stages of growth.
Unfavorable conditions in early growth stages may limit the size of the leaves (the photosynthetic factory). In later stages, unfavorable conditions may reduce the number of silks produced, result in poor pollination of the ovules and restrict the number of kernels that develop; or growth may stop prematurely and restrict the size of the kernels produced.
figure 53
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