Rice Yield Variations as Affected by Direct Seeding and Herbicide Application

Due to the dependency of direct seeding of rice on the application of herbicide and possibility of weed resistance to herbicides, the use of mixtures of herbicides is of considerable importance. To evaluate the effectiveness of consecutive applications of some herbicides with lower concentrations, including Thiobencarb, Pretilachlor, Bensulfuronmethyl, Ethoxysulfuron + Anilofos, Butachlor, and Propanil, on weed density, yield and yield components of rice (Oryza sativa L. cv. Hashemi) an experiment based on a randomized complete block design with eight treatments and three replications was conducted at the Research Farm of Faculty of Agricultural Sciences, University of Guilan in 2014. The results showed that plant height, seed yield, dry matter yield, harvest index, number of tillers and number fertile florets per panicle were affected by these treatments. Tandem use of Thiobencarb (9 day before sowing), Bensulfuronmethyl (9 day after sowing) and Propanil (30 day after sowing) affected weed dry matter and weed density by 92 and 98 %, respectively. The highest number of fertile floret per panicle (71 pcs) and tillers number per plant (14 pcs) were observed in plots where Thiobencarb, Bensulfuronmethyl and Propanil were used consecutively. In this treatment, seed yield and biological yield increased by 72 and 73 percent respectively as compared with that of control. Application of Pretilachlor caused phytotoxicity, where by reduced plant height and seed yield. The highest grain yield of rice (3092 kg.ha-1) was produced by consecutive use of Thiobencarb, Bensulfuronmethyl and Propanil. This treatment was more effective in reducing density of weeds and their dry matters than of two times hand weeding. The use of Thiobencarb followed by Bensulfuronmethyl and Propanil was the most effective treatment in this expriement.