Investigation of Possibility of Using Compatitive Cultivars of Rice to Reduce Butachlor Dosage in Barnyard Grass Control in Rice Fields

In order to distinguish the weed competitive cultivars of rice in reducing the use of Butachlor dosage, an experiment was conducted in a completely randomized block design (RCBD) with three replications in factorial arrangement of treatments. The experiment was done in research field of Islamic Azad University of Chaloos in 2009. The treatments included rice cultivars (Hashemi, Fajr and Shiroodi) and Butachlor herbicide doses (0, 1.5, 2, 2.5, 3, 3.5 L.ha-1). The results showed that lack of herbicide use caused the highest weed density and dry weight of Barnyard Grass. Also, the least yield (seed and biologic yield) and yield component (total number of tiller, percentage of fertilized tiller, number of spike in an square meter, number of spikelet in a spike, and percentage of full spikelet in a spike) was obtained in the presence of all cultivars. Weed density and dry weight of Barnyard Grass decreased and yield and yield component increased. An increase in Butachlor from 2.5 to 3.5 liter per hectare did not affect on weed density, dry weight of Barnyard Grass and yield and yield components significantly. In Shiroodi cultivar, the least weed density and biomass was obtained; it was recognized as the competitive cultivar in the presence of weed. Also in the presence of competitive cultivar of Shiroodi, the greatest (seed and biologic yield) and yield component (total number of tiller, percentage of fertilized tiller, number of spike in an square meter, number of spikelet in a spike, and percentage of full spikelet in a spike) was obtained in comparison with other cultivars.