Plant Population Density and Cotton Canopy Development

J. J. Heitholt


Okra-leaf cotton (Gossypium hirsutum L.) types exhibit many desirable developmental characteristics not expressed by normal-leaf types. Unfortunately, light interception, leaf area index (LAI), and lint yield of okra-leaf are often inferior to that of commercially grown normal-leaf cultivars. These limitations of okra-leaf are partially due to its poor adaptation to conventional wide-row spacings. Previous research indicated that okra-leaf grown in narrow-rows exhibited greater photosynthetic photon flux density (PPFD) interception [1-(below canopy PPFD X 100) / above canopy PPFD)] and 18% higher lint yields than okra-leaf grown in wide-rows. A second report indicated that optimal plant densities varied among leaf types (10 and 5 plants per square meter for okra- and normal-leaf, respectively) but not row spacing. However, it is not known what aspects of canopy development best explain the effects of plant density. Therefore, the objective of this study was to characterize cotton canopy development as affected by leaf type, plant density, and row spacing. Field experiments were conducted in 1991, 1992, and 1993 using both the okra- and normal-leaf isolines of DES 24-8 cotton with selected plant densities (2, 3, 5, 10, 15, and 20 plants per square meter). Narrow- (51-cm to 76-cm) and wide-rows (102 cm) were used for both leaf types and all plant densities. In 1991 and 1992, PPFD interception and LAI were determined periodically throughout the seasons and lint yield determined at maturity. In 1992, okra-leaf lint yield in 76-cm rows was highly correlated with early season (preflowering) PPFD interception. Normal-leaf canopies all reached greater than 90% PPFD interception by cutout. However, okra-leaf canopies that failed to reach 90% PPFD interception sometime during the growing season usually exhibited lower yields than those that did reach 90% PPFD interception. Using data from both leaf types, plots of yield vs. late season (at approximately cutout) LAI indicated that yield increased as LAI increased from 2 to 3, exhibited a plateau from as LAI ranged from 3 to 5, and declined if LAI reached greater than 5. Lint yields of okra-leaf in 76-cm rows (1992) and both row spacings (1993) were positively correlated to plant density and late-season LAI (r=0.80 to 0.96). In 1992, late-season LAI of normal-leaf at high plant densities (10 plants per square meter or greater) reached above 5. Under this environment, lint yields of normal-leaf were negatively correlated to plant density (r=-0.90) and to late-season LAI (r=-0.95), indicating that a late-season LAI of 5 or greater adversely affected yield. In 1993, LAI of normal-leaf never reached 5 and LAI values (at three stages of growth) were unassociated with yield. Overall, these findings indicate that (i) okra-leaf late-season LAI values below 3 and PPFD interception values that never reached 90% were associated with reduced yields and (ii) normal-leaf plant densities that result in excess late-season LAI may reduce lint yield.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1331
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998