Effects of Leaf Movement on Radiation Interception in Field Grown Leguminous Crops
II. Soybean (Glycine max Merr.)
Akihiro ISODA, Takao YOSHIMURA*, Toshio ISHIKAWA*, Peiwu WANG, Hiroshi NOJIMA and Yasuo TAKASAKI
Abstract: The effects of leaf movement on radiation interception were analyzed by the use of treated plants which were restrained from the leaf movement in the upper layer of the canopy. Two determinate soybean cultivars with different canopy structures, Nanbushirome (small canopy and leaflet type) and Miyagishirome (large canopy and leaflet type), were grown at two planting densities in the field. The pot experiment was also made to evaluate radiation interception under the conditions without mutual shading. Intercepted radiation of every leaflet of two plants within the canopy and one plant in the pot experiment was measured by the integrated solarimeter film for two consecutive days. The amount of intercepted radiation per unit ground area in the treated plants was larger than that in the control of both cultivars and indicated the ineffectiveness of the leaf movement on radiation interception. In general, Nanbushirome intercepted larger amount of radiation in every layer of the canopy in both field and pot experiment. The differences between the control and the treatment in Nanbushirome were large as compared with Miyagishirome. The leaf temperature of the uppermost layer in Nanbushirome was higher than the air temperature in the treatment, whereas it was at par with the air temperature in the control. The leaflets in the upper layer moved paraheliotropically to the sun rays during day time, thus the leaf movement is thought to regulate leaf temperature.
Key words: Canopy structure, Heliotropic movement, Integrated solarimeter film, Leaf temperature, Radiation interception, Soybean.