Interactions between genotype and density on the yield components of Zea mays: I. Production of dry matter by the shoot

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Abstract
SUMMARY: The interacting effects of genotype and density on the yield of dry matter by mature shoots were examined at Oxford, England. There were six hybrids, either pure dent or flint × dent crosses, together with two open-pollinated flint varieties of very early maturity. Over a range of 15 densities (5·0–30·8 plants/m2) for all the genotypes the relationship between the yield of the shoot and density can be adequately described by the reciprocal equation 1/w = A + Bp, where w = weight per plant, p = number of plants per unit area and A and B are constants for any particular set of conditions. Values of both 1/B (asymptotic yields) and 1/A (weight per plant at very low densities) were dependent upon the genotype. In a regression analysis between 1/w and p, the variance of 1/w was over 40 times as great at high as at low densities and a weighted analysis was necessary. Some hybrids approached maximal yields at 5 plants/m2, whereas others required a density of 10–15 plants/m2. The possible reasons for these interactions are discussed and improvements in experimental design suggested.