investigating effect of planting dates on density and dry weight of weeds and soybean cultivars (glycine max l.) yield

abstract limited number of herbicides are used to control weeds in soybean, which has herbicides resistance in consequence, so cultural weed management can be used in order to evaluate the effect of planting dates of soybean cultivars on weed management an experiment was conducted in randomized complete block design (rcbd) with four replications and with strip plot arrangement in sari. two planting dates (may 18th , june 7th and 27th ) and five soybean cultivars (bp, gk, 032, 033 and sahar) along with weed management:1-ethalfluralin(sonalan) 3 l/ha ppl, 2- ethalfluralin(sonalan) 3 l.ha-2 ppl + metribuzin (sencor) 700 g.ha-2 ppl, 3- ethalfluralin(sonalan) 3 l.ha-2 ppl + metribuzin (sencor) 700 g.ha-2 pre, 4-bentazon (bazagran) 3 l.ha-2 pem, 5- trilfluralin (treflan)3 l.ha-2 ppl + bentazon (bazagran) 3 l.ha-2 pem, 6-weedy check. results showed that the density of grass and broadleaf weeds and total density of weeds decreased in mid and late planting, compare to early planting of soybean. grass and broadleaf weeds weight were lower in mid and late planting date. weed total weight were lower in early planting date to others. soybean yield were higher in both early and mid planting. ethalfluralin(sonalan) 3 l.ha-2 ppl + metribuzin (sencor) 700 g/ha ppl and ethalfluralin(sonalan) 3 l.ha-2 ppl + metribuzin (sencor) 700 g.ha-2 pre reduced density and total weed weight, and these treatment gave the highest seed yield. 033 cultivar reduced grass and total weed density, and gk reduced grass weeds weight. bp, sahar and gk produced the highest yield, but bp had the highest in presence of weeds.