evaluation the effects of sowing date, cultivars and herbicides on different weed species and soybean (glycine max l.) yield

to evaluate the effects of sowing date, cultivars and herbicides on weed species control and soybean yield, a strip split plot layout in as a randomized complete block design with three replications was conducted in dasht-e-naz company sari-iran, in 2008. treatments included two planting dates (planting june 7th and 27th), soybean cultivars (bp, jk, 032, 033 and sahar) and herbicide applications (1 - ethalfloralin pre-planting (3 lit/ha) 2 - ethalfloralin pre-planting (3 lit/ha) + metribuzine (700 g/ha) as simultaneously application 3- ethalfloralin pre-planting (3 lit/ha) + metribuzine pre-emergence (700 g/ha) 4 –bentazon post emergence (3 lit/ha) 5 - trifloralin pre-emergence (3 lit/ha) + bentazon post emergence (3 lit/ha) and 6 – the weedy check). results showed dry weight of velvetleaf (abutilon theophrasti), wild melon (cucumis melo) and night shade (solanum nigrum) decreased with delay planting. on the other hand, bermuda grass (cynodon dactylon) and pigweed (amaranthus retroflexus) had less dry weights in early planting. all soybean varieties in delayed planting date resulted in reduction of weeds dry weight but in early plantingm, soybean yield was 28% higher than the late planting. ethalfluralin + metribuzin treatments as pre-planting and pre-emergence, reduced grass and broadleaf weeds dry weight in early and delayed planting dates respectively. by this mean, dry weight of weeds reduced in total the highest yield of soybean were achieved. bp, sahar and jk produced 3505, 3480 and 3472 kg/ha yield respectively in weedy conditions.