Effect of Sowing Dates and Types of Cover Crops on Soybean (Glycine max L.) and Weeds Interaction

The effect of planting time of cover crops on soybean -weed interaction, was assessed by experiment based on randomized complete blocks design with three replications in juybar during growth season of 2013. Treatments were included cover crops fenugreek (Trigonella foenum–graecum L.), winter veteh (Vicia sativa L.), Persian clover (Trifolium resupinatum L.), and chickling pea (Lathyrus sativus L.) simultaneously and three weeks after soybean sowing as well as two soybean cultivars under weed and non-weed conditions. The lowest yield of soybean was observed in weed infestation (7449.4 kg.ha-1) and the highest yield of soybean (3792.69 kg ha-1) was observed in the second planting date of winter veteh. While, maximum cover crops height, stem diameter, leaves number, dry matter and leaf size were observed at the first planting date of them. Meanwhile, at all three sampling stages, the infested soybean with weeds had the highest density and weed biomass, and the lowest weed density and biomass were also observed in winter veteh cover crop at the second planting date in all three stages. It seems that winter veteh as a living mulch can reduce the weeds growth with accelerating canopy closure; also, decreasing weeds competition with the main crops, incrased, crop yield.