CANOPY CHARACTERISTICS ASSOCIATED WITH DEFICIENT AND EXCESSIVE COTTONPLANT-POPULATION DENSITIES

Cotton (Gossypium hirsutum L.) genotypes exhibit variation in leaf typ es and leaf area index (LAI). The objective of this research was to ch aracterize canopy development and yield of two cotton leaf types grown in varying plant population densities. Field experiments were conduct ed in 1991, 1992, and 1993 with both the okra-leaf (low LAI) and norma l-leaf (high LAI) isolines of 'DES 24-8ne' cotton with selected plant population densities (5, 10, and 15 plants m(-2)). Photosynthetic phot on flux density (PPFD) interception (1991-1992) and LAI (1991-1993) we re determined periodically and final tint yield was determined at matu rity. 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 199 1 and 1992, early-season PPFD interception of okra-leaf at 10 and 15 p lants 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 i nterception and LAI limited yield of okra-leaf at 5 plants m(-2). In c ontrast 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, th e lower yields of normal-leaf at 10 and 15 plants m(-2) were apparentl y associated with late-season LAI values of 5.0 or greater, whereas th e 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 wa s higher for okra-leaf than for normal-leaf and (ii) a maximum LAI bet ween 4.0 and 5.0 was required to maximize cotton lint yields in this e nvironment.