1 Effect of rippled canopy on light competition between Soybean and Redroot pigweed (Amaranthus retroflexus) in Sole and Intercropping and b , Hamid Rahimian Mashhadi b Mostafa Oveisi , a , Goudarz Ahmdvand a Pershang Hosseini b Hassan Alizadeh Contact information: a: Department of Agronomy and Plant Breeding, Bu-Ali Sina University, Hamedan, Iran. b: Department of Agronomy and Plant Breeding, University of Tehran, Karaj, Iran. *Corresponding author email: hoseini.p@gmail.com ABSTRACT Field experiment was conducted to evaluate effect of canopy structure on growth analysis, light absorption and weed competition of two soybean cultivars in sole and mix cropping. A factorial design based on randomized complete block with three replications was carried out in field research station, University of Tehran, Karaj. Two soybean cultivars including Clark (tall) and Interprice (dwarf) were planted in sole and intercropping in competition with redroot pigweed at densities of 0, 2, 4 and 8 plant/m-2. Light absorption and canopy structure assessed in canopy closure. The results realized that, in mixed cropping Redroot pigweed had less CGR (4 g/m2d) and less cumulative biomass (234 g/m2) compare to sole cropping. Canopy surface in intercropping increased 20% compared to the sole cropping and the light extinction is occurred in 60 cm of soybean high. Light absorption in the development time of canopy for Clark and Interprice were 84% and 64% respectively. This tow cultivars supplementary complete each other for light absorption because of the height difference between them and inter specific competition dominated by intra specific competition. Keywords: light competition, canopy structure, tall and dwarf cultivars INTRODUCTION Intercropping is one of the beneficial systems for achieving sustainable agriculture. A matchable mixed cropping is an effective approach for utilization environmental resources and it can be more useful than a single cropping (Fukai & Trenbath, 1993). In implementation of mixed cropping for sustainable systems should be noted that, compatible plants are those have the biggest difference in the use and uptake of resources (Vandermeer, 1989). Light in weed-crop ecosystem adjust many aspects of growth, development and competition, it can’t be saved and must be consumed immediately, so the principles for light competition is different from other sources. Ability of shading on adjacent plants and absorb more part of the radiation determine competitive ability of species (Stoller et al., 1987). Light inhibitory effect of one specie on another species is one of the main competition factors and affected by leaf area index and light extinction coefficient (Mclachlan et al., 1993). Canopy displays spatial arrangement of foliage on a plant population. In mixed canopy, light absorption affected by LAI, plant height, leaf area vertical distribution of species (Zand et al., 2004; Rajcan & Swanton, 2001). This study carry out to evaluate effect of tow soybean cultivars mix cropping with different growth characteristics (tall and dwarf) on redroot pigweed control and studying intercropping as a management tool in sustainable agriculture.