Plant Geometrical Structure and Leaf Irradiance in Cotton: II. Measurement of Cotton Plant under Tropical Conditions

Abstract

Leaf orientation behavior of cotton plants (Gossypium hirsutum L. cv. SSR60) at two different stages of development were studies in the field under tropical conditions. Electromagnetic digitizing system was used for leaf angle and leaf position measurements at three different periods of two hours during the day. Leaf azimuth distribution of SSR 60 cotton variety was not uniform. Cotton leaves tended to face the sun in the morning. But tended to lag at noon and in the afternoon. Most of cotton leaves inclined between 15^o-45^o during the day. Cotton leaves showed a diaheliotropic movement throughout the day. They oriented more diaheliotropically at noon, but less in the morning and in the afternoon at both two stages of development. Because of actual leaf azimuth distribution, cotton plants could have 15-30% of advantage in direct radiation interception compared to uniform leaf azimuth distribution. Without a diurnal leaf orientation, cotton plants would intercept less direct radiation in the morning and in the afternoon. The ecological significance of this leaf orientation behavior under tropical conditions is also discussed.