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The environment of hybrid corn (Zea mays L.) was changed at intervals over the life cycle by removing every other plant of plants that were equispaced in rows 97 cm apart at a population of 44,500 plants/ha. Because the low plant population environment (LPE) resulting from these thinning treatments gave great improvement in the light environment over lower shoot and relatively small changes in other environmental factors, plant response was attributed mainly to changes in light environment. The number of ears per plant was 1.76, 1.57, and 1.70 during 1964, 1965, and 1966, respectively, for the 22,250 plants/ha check, which received LPE during the entire life cycle. The 44,500 plants/ha check, which received no LPE, had 1.10, 1.05, and 1.02 ears per plant, respectively. In the three seasons, changes in number of ears per plant in response to LPE imposed at different times indicated that 56, 79, and 78% of the above reduction in ears per plant between 22,250 and 44,500 plants/ha populations took place from the time the first plants silked until soon after all plants had silked — about 10 to 12 days. The rapid abortion of ears during silking and just afterward, under the unfavorable light environment of the 44,500 plants/ha population, establishes this as an important critical period for light competition in the plant community. Individual plants within the community began aborting ears under the unfavorable light environment as early as 3 or 4 days before silks emerged and continued until about 8 days after silks emerged.
Key Words: Zea mays L. • Corn • Light response
2 Associate Professor of Agronomy, Florida Agricultural Experiment Station, Gainesville, Fla., 32601.
Received for publication May 8, 1969.
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