Competition of Red Root Pigweed (Amaranthus retroflexus) with Two Soybean (Glysine max) Cultivars under Sole and Intercropping Systems 1- Soybean Yeild and Redroot Pigweed Growth Analysis

Field experiment was conducted in the College of Agriculture and Natural Resources of Tehran University, Karaj to evaluate the effect of intercropping two soybean cultivars on redroot pigweed biomass. The experimental design was a completely randomized block with factorial arrangement of treatments with three replications. Two soybean cultivars including Kelark (tall) and Interprice (dwarf) were planted in sole and under intercropping in competition with redroot pigweed at (0, 2, 4 and 8 plants/m2). The results revealed that yield of both cultivars were decreased with increasing redroot pigweed density, but the yield of Interprice was reduced 45% more than Kelark. In comparison to Interprice, yield of Kelark in intercropping was higher than sole cropping. LER calculated in intercropping under weed free condition was 1.11. Under intercropping, redroot pigweed had lower LAI (0.58), cumulative dry matter (283 g/m2) and CGR (4.7 g/m2day) compared to when grown with sole crops.