عنوان مقاله [English]
Introduction: Soybean is one the strategic crops which contributes to provide a part of food in 43 countries. Soybean planting area and production in the world are 102 million hectare and 261 million tonnes respectively. Its planting area was 764000 ha in Iran in 2013. Mazandaran, Guilan and Golestan are the most soybean producing province in Iran. Golestan with 53405 ha and 90000 tonnes production is the first soybean producer in Iran. Weed competition is considered one of the most important inhibitor factors, which not only causes yield losses but also, reduction in quality by interference in soybean growth and development. Yield reduction by weeds was reported by 28% under the Caspian Sea climate. Mean yield loss for one plant/square meter, has been reported up to 30% and it may reach to 80% in higher weed density. Therefore study of soybean weed control is avoidable.
Materials and Methods: In order to control weeds in soybean fields, an experiment was conducted as Randomized Complete Block Design (RCBD) with three replications in Gorgan agricultural research stations in a field that had enough weed infection. The treatments were triflutalin (treflan 48% EC) 2.5 l/ha, metribuzin (sencor 70 % wp) 0.5 l/ha, metribuzin 0.5 l/ha+ trifluralin 2.5 l/ha, imazethapyr (persuite 10% SL) 0.6 l/ha, imazethapyr 0.8 l/ha as pre plant, oxyfluorfen (goal 24% EC)0.75 l/ha, pendimethalin (stomp 33% EC) 3 l/ha, imazethapyr 0.6 l/ha, imazethapyr 0.8 l/ha, metribuzin 0.3+ imazethapyr 0.6 l/ha, pendimethalin 2.5 l/ha + imazethapyr 0.6 l/ha as pre-emergence, oxyfluorfen 0.5 l/ha, bentazon (basagran 48% SL) 1.5 l/ha, imazethapyr 0.6 l/ha, imazethapyr 0.8 l/ha, bentazon+ imazethapyr 0.6 l/ha, cletodim (select super 12% EC) 1l/ha + imazethapyr 0.6 l/ha as post-emergence at 4-6 leaf stage and weed free treatment as a control. Plot size was 1.4m×10m. Seed rate, row spacing, cultivar and other cultivation method was done by conventional method. Each plot was divided to two parts, which one part was treated by herbicides and the other part was held untreated and considered as control treatment. In weed free check treatments, weeding was done with 10 days interval but in weedy check no weeding and no chemical weed control was done. To investigate the effect of treatments on weed number, weed fresh and dry weight, a quadrate of 0.5 × 0.5 m was fixed in each plot (so that it represents the weeds of whole plot). Before harvesting, all of the emerged weed species in fixed quadrates were identified, counted and their dry weight was measured after drying in 75 celcius degree oven for 72 hours. At harvest 5 plants per plot were randomly selected and yield components were measured. For yield, two 0.5 m2 quadrates were harvested in each plot and grain yield and biomass were determined. Qualitative evaluation of soybean, which includes chlorosis and necrosis in leaves, was done based on EWRC standard method. Data analysis of variance was performed using SAS software version 9.1 and the means were compared using LSD test at 5% level. Since field data were not normal, a logarithmic and root square ( ) transformation was used to normalize data.
Results: The results showed that all treatments caused reduction in weed number percentage than control treatment. The highest reduction was observed in imazethapyr 0.8 l/ha (pre plant) at par with hand weeding treatment. Pendimethalin 2.5 l/ha + imazethapyr 0.6 l/ha, metribuzin 0.3+ imazethapyr 0.6 l/ha as pre emergence had the next rank. The highest yield after hand weeding was obtained in imazethapyr 0.8 l/ha (pre plant) followed by pendimethalin 2.5 l/ha + imazethapyr 0.6 l/ha and imazethapyr 0.8 l/ha as pre emergence. Therefore based on the results of this study using of imazethapyr 0.8 l/ha as pre plant or pre emergence are recommended for weed control in soybean fields and mixing of this herbicide with pendimethalin is also conducive to increasing the herbicide spectrum. Application of this herbicide (imazethapyr 0.8 l/ha) at 4-6 leaf stage of weeds, to obtain higher yield is possible too. The results of this experiment showed that some of post-emergence herbicides caused a little phytotoxicity on soybean (oxifluorfen 0.5 liters / ha (20%), Bazagaran + Persoite (15%), Coltodium + Persoite (10%), Bazagaran (5 to 10%), Persuite 0.8 liters per hectare (lower than 5%)). It should be noted that the phytotoxicity of all treatments was eliminated in the later stages of growth.
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