Comparison of the effects of the recommended and reduced rates of Bentazon application on weed control and on growth and seed yield of soybean cultivars

An experiment was conducted in split plots using the randomized complete block design in three replications during cropping season 2011 2012 to study the effects of different rates of application of the herbicide Bentazon on weed control and on seed yield of soybean cultivars. The factors investigated were the three cultivars of Hill, Sari, and Line 032 (as the main factor), and the five rates of 2 L/h (the recommended rate), 75%, 50%, and 25% of the recommended rate (1.5, 1, and 0.5 L/h, respectively) and the control of not applying Bentazon (as the sub factor). Results of the experiment showed that the effects of the cultivars of soybean and the mutual effects of the rate of Bentazon application and cultivar on yield components including the number of pods on the main stem, the number of pods per plant, the number of seeds per pod, the 100 - seed weight, and finally seed yield were not significant at the one percent probability level, while the effects of applying different rates of Bentazon on the features studied were significant at the one percent probability level. Comparison of the means of data regarding the application of Bentazon indicated that the number of pods on the main stem, the number of pods on lateral shoots, the length of filled pods, the number of seeds per pod, the 100 - seed weight, and the number of unfilled seeds decreased with an increase in the rate of application of Bentazon: the largest number of seeds per pod (78.77), the maximum number of pods on lateral shoots (75.6), the greatest number of seeds per filled pod (2.61), and the maximum 100 - seed weight (18.10 g) were achieved at the maximum rate of Bentazon application. These results also revealed that the weight of dry matter produced and the soybean seed yield also increased with a rise in the rate of application of Bentazon: the greatest weight of dry matter (89.73 g/half a square meter) and the largest seed yield (318 g/per half a square meter) were achieved at the maximum rate of Bentazon application (the recommended rate), while these two features declined when the rate of application of Bentazon decreased. In the comparison of the mutual effects of cultivar and rate of application of Bentazon, it was also revealed that seed yield in all three cultivars went up with an increase in the rate of Bentazon application. Results obtained showed that the greatest seed yield (312.7 g/half a square meter) was achieved at the maximum rate of Bentazon application in Line 032, and that the smallest (35.5 g/half a square meter) belonged to the cultivar Hill in the control treatment (in which no Bentazon was used).