Abstract : Detailed features of solar radiation distribution and penetration in soybean communities were examined using integrated solarimeter films for 2 days. Five cultivars (c.v. Tsurukogane, Nanbushirome, Enrei, Tachinagaha and Miyagishirome) were grown under field conditions and in pots for comparison. All of these cultivars except Tsurukogane had leaf concentration in the upper layers of the canopy. Tsurukogane and Nanbushirome had smaller leaflet areas in the upper of the canopy, whereas Enrei, Tachinagaha and Miyagishirome had larger leaflets in the upper layer. The higher the intercepted radiation and the smaller the leaflet size, the larger the difference in intercepted radiation' between the edge and the center of the leaflet. The mean radiation penetrating leaflet was around I MJ m~2 2 days~1 and penetrated radiation against intercepted radiation on the leaf adaxial surface ranged from 13 to 27%･ The differences were larger in the cultivars with larger leaflets and smaller in the cultivars with smaller leaflets. A canopy structure with smaller leaflets and smaller leaf area in the upper layer of the canopy may be advantageous for radiation transmission and distribution.

Key words : Canopy structure, Integrated solarimeter film, Penetrated radiation, Radiation distribution, Soybean