CANOPY CHARACTERISTICS ASSOCIATED WITH DEFICIENT AND EXCESSIVE COTTON PLANT-POPULATION DENSITIES

Cotton (Gossypium hirsutum L.) genotypes exhibit variation in leaf types and leaf area index (LAI). The objective of this research was to characterize canopy development and yield of two cotton leaf types grown in varying plant population densities. Field experiments were conducted in 1991, 1992, and 1993 with both the okra-leaf (low LAI) and normal-leaf (high LAI) isolines of 'DES 24-8ne' cotton with selected plant population densities (5, 10, and 15 plants m(-2)). Photosynthetic photon flux density (PPFD) interception (1991-1992) and LAI (1991-1993) were determined periodically and final tint yield was determined at maturity. Averaged across years, yields of okra-leaf in narrow rows were 6 to 7% greater at 10 and 15 plants m(-2) than at 5 plants m(-2) In 1991 and 1992, early-season PPFD interception of okra-leaf at 10 and 15 plants m(-2) was greater than at 5 plants m(-2). In 1992 and 1993, okra-leaf at 10 and 15 plants m(-2) attained an LAI of 4.0 to 4.5 whereas the 5 plants m(-2) density failed to reach 4.0. Therefore, both PPFD interception and LAI limited yield of okra-leaf at 5 plants m(-2). In contrast to okra-leaf, lint yields of normal-leaf were 4 to 8% greater at 5 plants m(-2) than at 10 and 15 plants m(-2). In 1991 and 1992, the lower yields of normal-leaf at 10 and 15 plants m(-2) were apparently associated with late-season LAI values of 5.0 or greater, whereas the 5 plants m(-2) density developed late-season LAI values ranging from 4.0 to 4.8. These findings indicate that (i) optimal plant density was higher for okra-leaf than for normal-leaf and (ii) a maximum LAI between 4.0 and 5.0 was required to maximize cotton lint yields in this environment.