Changes in Leaf Orientation and Canopy structure of Cotton (Gossypium hirsutum L.) under Different Plant Population Densities

Abstract

            The effects of plant population density on diurnal changes of leaf orientation behavior and canopy structure of cotton (Gossypium hirsutum L.) during growing season were studied under field conditions by using an electromagnetic digitizing system for characterizing the canopy structure. At high density (80x9 cm-138,890 plants/ha), leaf area index (LAI) developed more rapidly than medium density (80x18 cm-69,440 plants/ha) and low density (80x40 cm-31,250 plants/ha), respectively, due to a greater number of leaves per plant.

              At the same plant age, plant characteristics, except leaf area plant and leaf area expansion rate (LAER), of high-density canopy differed from medium-density canopy while those expect leaf size differed from low-density canopy. Medium–density canopy did not show significant difference of plant characteristics compared to the low-density canopy, except leaf size and number of leaves per m². At the same LAI stage, the cotton plants under high density had different plant characteristics, except leaf size and number of leaves per m², from those under medium density. However, the plant characteristics, except internode length and number of leaves per m², of high – and medium- density canopies did not differ significantly from low-density canopy.

               Leaf orientation behavior did not differ significantly between plant densities, particularly at the same stage of LAI. Cotton leaves tended to face the sun more at noon than in the morning and in the afternoon during growing season. Changes in horizontal and vertical distributions of leaf area were not significantly altered during the day by diurnal leaf orientation, but they differed significantly during growing season. These changes were significantly different between the three plant population densities at the same plant age. However, there were no significant differences in horizontal and vertical leaf area distribution at the same stage of LAI among the three plant population densities. This quantitative description of canopy structure may be useful for developing mathematical models of light interception in the canopy of cotton.