The role of planting date and rice cultivars on the effect of weed on yield and some agronomic traits in dry-bed seeding system

To investigate the effect of planting date on yield and some agronomic traits in local and high-yielding rice cultivars in direct cultivation by dry-bed seeding system was conducted in the form of a split-plot in a randomized complete block design with three replications. The main plot of planting date in three levels (June 15, June 25, and July 5) and four rice cultivars including two local cultivarsChampa and Red anbori and cultivars High-yielding and improved Danial and Shafagh was grown as a subplot at each planting date. Then, each plot was divided into two parts. The upper part of plot was not weeding and was considered as a control and the lower part of the plot was removed by hand weeding. Based on the results, the effect of planting date and cultivar on biological yield, grain yield, and the number of spikes per square meter under weed control conditions was significant at the level of one percent. In this experiment, the highest yield was observed on the date of the first planting in the high-yielding cultivar Shafagh and at the rate of 5253 kg/ha. The results showed that grain yield loss due to weed presence was different depending on planting date, so that the highest and lowest production loss with the average of 1815 and 1090 kg/ha was related to the first and third planting date, respectively. Among rice cultivars, a decrease in grain yield of 40.85 and 32.95 percent was observed in high-yielding cultivars and local cultivars, respectively.