Weed Interference and Growth Performances in Soybean (Glycine max (L.) Merr.), as affected by Weed Density and Types of Weed

The aim of this study was to evaluate of the density for four weeds on growth inhibition against soybean (Glycine max) (Chiang Mai 2 variety). The experiment were interfered with four weeds namely wild poinsettia (Euphorbia heterophylla), eclipta (Eclipta prostrata), slender amaranth (Amaranthus viridis) and spiny amaranth (Amaranthus spinosus) against soybean (G. max). The number of four weeds interfered with soybean planting divided into five treatments; 0 (control treatment) 4 8 12 and 16 plants/m2. Stem height, leaf area, fresh weight of aboveground part and dry weight of aboveground part of soybean were measured at 28 days after planting. The results showed that the increase of number of four weeds resulted in the increase of inhibition of all growth performance in soybean. The planting of soybean interfered with the weeds for 16 plants/m2 exhibited that the maximum of inhibitory degree (52.61%) followed by the planting of soybean interfered with the weeds for 12 8 and 4 plants/m2 by 40.04, 25.94 and 13.08%, respectively. The planting of soybean interfered with spiny amaranth (A. spinosus) exhibited that the highest of inhibitory degree (35.41%), followed by the planting of soybean interfered with eclipta (E. prostrata), wild poinsettia (E. heterophylla) and slender amaranth (A. viridis) showed the inhibitory degree for 34.35, 31.65 and 30.27%, respectively. This result presented the effects of density of weeds against soybean on growth parameters (stem height, leaf area, fresh weight of aboveground part and dry weight of aboveground part) as well as suggested that the planting of soybean should be the planting of soybean were not interfered with different weed density in order to the minimization of weed competition as well as the optimum method for weed arrangement.