weed management methods in direct-seeded rice (Oryza sativa L.)

Background and objectives: Rice (Oryza sativa) is a major cereal crop and staple food for more than half of the world's population. About 90% of the world's rice is produced and consumed in Asia. Iran is one of the arid and semi-arid regions and due to the lack of water in many parts of the country, the area under rice cultivation decreases. Direct rice cultivation is a good way to save water. The most important challenge in this cultivation system is weed control. The traditional methods of weed control in rice include hand-weeding by hoe or hand pulling, but this is becoming less common because of labour scarcity at critical time of weeding and increasing labour costs. Herbicides play a key role in weed control and are used extensively today. Therefore, this experiment was conducted to evaluate the effectiveness of different weed management practices for direct seeded rice at varying row spacing.
Materials and methods: This study was conducted to investigate the effect of planting distance on rows and herbicides on weed suppression and direct rice cultivation performance in the research farm of Sari Agricultural Sciences and Natural Resources University as a factorial experiment in a randomized complete block design with three replications in 2019. Distance between plants at two levels of 3 and 5 cm and chemical management of weeds in five levels of weed-free (control), weed-infested (control), application of trifamone + ethoxysulfuron herbicide 30% (council active) at the rate of 150 g ha-1 in stage of 2 up to 6 leaves of weeds, application of bisopiribac sodium herbicide OF10% (nomini) at the rate of 250 ml ha-1 in stage of 2 to 6 leaves of weeds and application of a mixture of two herbicides halofop butyl OD 20% with 2.5 liters ha-1 with basagran (bentazone) were 3 liters ha-1 in the 2 to 6 leaves stage of the weeds.
Results: Results showed that although planting row spacing had no effect on the desired traits; however, weed management had a significant effect on the studied traits. Visual evaluation of weed damage in two evaluation stages (15 and 30 days after spraying) showed that among the chemical control treatments, trifamone + ethoxysulfuron herbicide was superior to other herbicides with 75 and 83.33% weed control, respectively. The lowest weeds biomass was observed in 6 weeks after spraying (20.50 g m-2) and 10 weeks after spraying (20.83 g m-2) in trifamone + ethoxysulfuron herbicide treatment, which was not significantly different with weed free (control). The highest height of rice plants (103.17 and 98.41 cm) was observed in the complete weed control and trifamone + ethoxy-sulfurone herbicide treatments, respectively. It is worth mentioning that the maximum biological yield of rice (6244.4 and 5808.4 kg ha-1) and grain yield (2391.218 and 2290.27 kg ha-1, respectively) was observed in weed-free (control) and application of triafamone + ethoxysulfuron herbicide. According to the results of this experiment, the use of trifamone + ethoxysulfuron herbicide at the rate of 150 g ha-1 is recommended for proper control of weeds in direct rice cultivation.
Conclusion: The highest and lowest height, number of tillers and spike length were observed in weed-free control treatment and weed-infected control treatment. Among the herbicides used in this experiment, in the treatment of triafamone + ethoxysulfuron with better weed control, In plant height, tiller number, spike length and number of seeds per spike were superior to other herbicides. According to the results of the experiment, the application of the herbicide triafamone + ethoxysulfuron, while better control of weeds, can increase grain yield.