Genotypes and Plant Densities for Narrow-Row Cotton Systems. II. Leaf Area and Dry-Matter Partitioning

Interest in production of narrow-row cotton (Gossypium hirsutum L.) is increasing. Plant characteristics considered important for cultivars grown in 1-m row spacings may not be the same for plants grown in 0.76-m spacings. This field study was conducted to determine the influence of genotype and plant density on accumulation and allocation of dry matter in a narrow-row production system. Five genotypes representing a wide range in size and growth habit were grown in factorial tests at 5,10, and 15 plants m⁻² at the U.S. Cotton Research Station in Shatter, CA, in 1984 and 1985. Growth measurements were made four times during each season. Increasing plant density increased mean leaf area index (LAI) and total dry matter of genotypes at all sample dates but decreased harvest index (HI) from 0.58 to 0.53 at maturity. Genotypic differences in LAI and total above-ground dry matter became apparent only after anthesis. Mean season-end dry matter ranged from 9.78 Mg ha⁻¹ for the short determinate genotype 2086 to 10.88 Mg ha⁻¹ for ‘Acala SJ-2’. Final mean HI ranged from 0.66 for 2086 to 0.47 for Acala SJ-2. Height and vegetative growth rates (HGR and VGR) per 100 heat units (HU) were closely negatively associated with fruit growth rates (FGR) between the June and August sample dates. Including leaf area growth rate (LAGR) with FGR as a FGR/LAGR ratio as the independent variable improved r² from 0.59 to 0.81 for HGR and from 0.69 to 0.90 for VGR. Node growth rate (NCR) was only minimally sensitive to the FGR/LAGR ratio. These results show that vegetative development during early fruiting is related to size and earliness of the reproductive sink and growth rate of the source. Cultural practices that are presently used for cultivars with a low FGR/LAGR ratio may not be ideally suited for more determinate cultivars with a high ratio. This research was supported by a grant from the California Dep. of Food and Agric. Cotton Pest Control Board.