) GLYCINE MAXL. MERR( تاثير زمان وجين علف هاي هرز بر عملكرد و اجزاي عملكرد سويا

The effect of weeding time on yield and yield components in Soybean [Glycine max (L.) Merr]

To investigate the critical period of weed control in soybean, an experiment was conducted in Eraghi-Mahalleh Research Station, located at 7km of north Gorgan, Golestan provience in 1998. The experiment comprised of 14 treatments, which were compared in+ a complete block design with 4 replications. In this experiment the weeding time and its relation to reduction of soybean seed yield and yield components were investigated. The treatments were divided in two groups: The first group was kept totally weed free and the second one was kept weed infested up to some defined phenological growth stages of soybean. An exponential relationship between soybean seed yield and weed dry weight was observed. Continuation of weed competition to the later stages of crop development caused significant decreasing of yield components pod number per plant was the most important factor and had a highly positive and significant correlation with yield production (R-0.99). Seed number per pod and thousand-seed weight was less effective on final seed yield. The peak competition period of weeds in soybean crop was between formation of the third (V3) to seventh node (V7). If the weeds are controlled within this period, soybean would be protected against a significant seed yield reduction.