The Role of Agronomical Management on Reduction of Weed Damage in Organic Sesame (Sesamum indicum L.) Production System

Abstract Background and Objective: In organic farming, soil nutrients management by using organic fertilizers is one of the effective methods to the weed control.   Materials and Methods: This experiment was conducted in the organic field of Razi University as split plot based on randomized complete block design with three replications in 2018 growing season. The experimental treatments included farmyard manure (mixture of cattle and sheep manure) at three levels (0, 10 and 20 t.ha-1, FM0, FM10 and FM20, respectively) as main factor and the cultivation of green manure (non-cultivating green manure, hairy vetch, berseem clover and fenugreek) as sub factor.   Results: Johnson grass, Bindweed and Licorice were the dominant weeds in both sampling, which they had 48, 22.5 and 9.8% of relative weeds density at the first sampling, and 48, 14.4 and 18.3% of relative weeds density at the second sampling. Consumption of 10 and 20 t/ha of farmyard manure increased the green manure biomass by 9.8% and 37.7%, respectively. Fenugreek, berseem clover and hairy vetch were produced 7219, 5799 and 3564 kg.ha-1 biomass, respectively. The highest weed biomass at the 1/3 of primary and end of the growing season was obtained in non-fertilizer condition. Application of 10 and 20 ton/ha of farmyard manure reduced weed biomass by 16.4% and 29.1% at the 1/3 of primary growth season, and by 9.3% and 54.1% at the end of the growing season, respectively. Without green manure application, weed density in the first and second sampling were 244.4 and 48.5 plant/m2, respectively. By sowing of hairy vetch, berseem cloverand fenugreek, weed density was reduced by 12.5%, 43.2% and 36.3% in the first sampling and by 5.6%, 35.5% and 26.4% in the second sampling, respectively. All varieties of green manure at different levels of farmyard manure increased the grain yield of sesame. Finally, the positive effect of organic fertilizers application on weed growth and damage resulted in improved grain yield. The amount of this improvement compared to the control condition with consumption of 10 and 20 t/ha of farmyard manure was 18.8% and 27.6%, respectively, and with the application of hairy vetch, berseem clover and fenugreek was 30.7%, 35.9% and 45.5%, respectively. The highest grain yield (1929 kg.ha-1) was obtained from fenugreek application at 20 level of farmyard manure and the lowest amount (918 kg.ha-1) under control conditions.   Conclusion: Management of organic fertilizers can reduce the yield loss due to weeds by changing competition conditions in favor of the crop. According to the results study, depending on the type of organic fertilizer used in organic farms, an improvement of grain yield of sesame between 18 to 45% will be expected. The best treatment in which, the highest grain yield was produced and had the lowest density and dry weight of weeds was achieved by consuming 20 /ha of manure and using berseem clover as green manure. Therefore, it is introduced as a suitable treatment combination.