Characterizing the interactive interference of rice with barnyard grass (Echinochloa crus-galli) and bulrush (Schoenoplectus planiculmis) weeds in a replacement series experiment

In order to investigate the role of inter-species interference and competitive outcome of barnyard grass (Echinochloa crus-galli) and bulrush (Bolboschoenus planiculmis) weeds with Guilaneh cultivar of rice, a factorial experiment with two factors including weed species (barnyard grass and bulrush) and rice: weed ratios in each pot (0: 4, 1: 3, 2: 2, 3: 1, and 4: 0) was conducted as a randomized complete-block design with three replications. The results showed that, except for height, all other traits of rice decreased more in competition with barnyard grass than competition with bulrush. The percentage of more reductions of traits in rice-barnyard grass competition than rice- bulrush competition, averaged over planting ratios, were 10 and 21% for biological yield, 12 and 23% for seed yield, 10 and 21% for number of panicle, 13 and 25% for number of filled seeds, 7 and 16 for total number of seeds, and 10 and 17% for number of tillers on pot and single plant levels, respectively. These results, along with the replacement series diagrams studies have indicated the severe competition of barnyard grass with rice plants. However, no significant difference in the competitive effect of the two weed species, as well as the insignificant dominance index and the ratio of barnyard grass and bulrush competition, indicates the importance of bulrush as a new weed in rice fields. Therefore, effective management of bulrush in addition to barnyard grass should be taken into consideration in the development of the weed management programs in paddy rice fields.