The Response of Different Rice Cultivars (Oryza sativa L.) to Different Weed Management Methods under Direct Cultivation System

Direct seeding of rice is one of the most common farming methods in the world. Economic efficiency, faster and easier cultivation, reduction of growth period and earlier maturity (7-10 days), needing to less labour, higher water efficiency, more mechanization and reduction of rice vulnerability due to end-of-season drought are some benefit of direct rice cultivation; while, the most important problem in this planting system is weed control, and if weeds are controlled properly; the yield of rice in direct seeding will be almost equal to that of transplanting system. So, this study was conducted to evaluate the effect of weed management methods on different cultivars of rice in direct seeding system.

This research was performed as a factorial in randomized complete block design in three replications at Rice Research Institute, Amol in 2018. Treatments include three different rice cultivars of Tarom Hashemi, Shiroodi and Neda under six weed management methods (no weeding, twice weeding (40 days after emergence and in the earing stage), using rice husk mulch (0.5 kg m-2 after sowing), application of triafamone+ethoxysulfuron herbicide (30 g ai ha-1 in 5 days after emergence in two-leaf stage), application of triafamone+ethoxysulfuron herbicide (30 g ai ha-1 in 5 days after emergence in two-leaf stage) + weeding (40 days after emergence) and complete weeding (all weeds are removed during the growing season) were considered. The studied traits included: plant height, tiller number, panicle length, 1000-grain weight, filled grain number, empty grain number, panicle number per square meter, grain yield, biological yield and total weed density and dry weight.

The results showed the highest plant height (137.7 cm) and number of tillers (24.7) was obtained in Tarom Hashemi and Shiroodi cultivars under complete weeding, respectively. The results of mean comparison of the main effects of the experimental treatments indicate that the filled grain number in Tarom Hashemi, Neda and Shiroodi cultivars were 67.6, 69.3 and 90.1 per ear and 1000-seed weight in these cultivars, was 19.9, 18.6 and 21.1 g, respectively. When Shiroodi cultivar had more seeds per ear and 1000 seeds weight. Also, the maximum filled grain number (94.9) and the highest 1000-seed weight with 22.7 g was observed in the complete weed control treatment. The highest panicle number per square meter (316.7) was related to Shiroodi cultivar and complete weed control, which had no significant different with herbicide + weeding and twice weeding in the same cultivar, as well as complete weeding in Neda cultivar. The highest grain yield (8192.5 kg ha-1) was observed in Shiroodi cultivar + complete weeding, which had no significant different with Neda + complete weeding and Shiroodi + herbicide + weeding. Lack of weed control in Tarom Hashemi, Neda and Shiroodi cultivars reduced 38.2, 63.3 and 61.7% of grain yield compared to complete weed control, respectively. The results showed that at all three stages of sampling, the lowest weed density and dry weight in all three sampling stages was related to herbicide + weeding treatment in Shiroodi cultivar which had good control over weed and was able to reduce weed density and its dry weight.

In general, it can be concluded that although the yield of rice in the direct planting system was the highest in the absence of weed contamination; however, since the application of triafamone+ethoxysulfuron herbicide along with weeding caused reduction the density and dry weight of weeds, and also, improved the yield and yield components of all three rice cultivars, so this management method can be used to control weeds more effectively and achieve proper yield in this system.