Response of Two Cotton Genotypes to Five Equidistant Spacing Patterns

High population densities have been proposed as one way of achieving earlier maturity in cotton (Gossypium hirsutum L) by increasing the potential number of early fruiting points. But competition among closely spaced plants may adversely affect initiation and set of fruit. Theoretically, competition can be reduced by improving the uniformity of plant distribution. A year field study was conducted to determine the morphological and agronomic reactions of cotton to intraspecific competition over a wide range of plant populations within equidistant spacing configurations. Response to equidistant plant spacing was studied using two genotypes of upland cotton (Gossypium hirsutum L.) with contrasting plant types and five population densities ranging from 38,750 to 620,000 plants/ha in patterns where distance between plants within the row equaled the distance between rows. Vegetative and fruiting components were measured and dry weight determinations were made after destructive fractionation at three harvest dates. Yield, earliness, and fiber quality data were accumulated from weekly harvests of mature bolls. As plant population increased, dry weight per unit land area of all plant components increased except vegetative branches, which decreased. Leaf area index and the number of nodes to the first fruiting branch also increased with higher populations. A smaller, more compact plant developed as plant density increased, which was indicated by reductions in plant height, stem diameter, and number of branches. Boll size, number of seed/boll, seed index, and lint index were all reduced as plant spacing decreased. Retention rate of fruiting forms was apparently much lower in the very high plant densities. Population levels of 79,000 and 155,000 plants/ha were earlier maturing and produced higher lint yield than population levels on either side of this range. These results generally agree with those of investigations of cotton spaced in 1-m rows. There was no evidence that high population densities in equidistant spacing patterns improve earliness or yield.