Characterizing the competitive traits of watergrass (Echinochloa oryzoides) as a new-introduced, and barnyardgrass (E. crus-galli) as a common weed species in rice

early watergrass (Echinochloa oryzoides) is considered as a new-introduced species and then as a potential invader. Investigation of competitive traits of this species, in comparison with barnyardgrass (E. crus-galli), one of the most important weeds in rice fields of Guilan province, would be useful to determine its spreading possibility as an aggressive weed. Therefore, competitive traits of two weed species in rice were studied in this research. This field experiment was conducted at Rice Research Institute of Iran, Rasht as a factorial based on randomized complete block design with three replications. treatments consisted of weed species ((barnyardgrass and watergrass) and plant proportions of 0:4, 1:3, 2:2, 3:1, and 4:0, weed:rice in each hill. By substituting rice and weed seedlings in each hill, different densities were created. To study the growth and development of rice and weed, 5 stages of destructive sampling were taken every 14 days in addition to the last sampling was done at harvest (90 days after transplanting). About 8 weeks after transplanting, the highest height was related to watergrass, however at the harvest, barnyardgrss height increased. lower leaf area index of watergrass comparing with barnyardgrass at about 10 weeks after transplanting indicating less leaf area duration for this species. at the harvest time, around 13 weeks after transplanting, higher leaf but lower total dry weight was recorded for watergrass than barnyardgrass. In general, new-introduced as compared to common weed species had lower final height, leaf duration, and total biomass, but earlier tillering stage, leaf development, and booting. Rising in the ratio of each species at the planting proportion caused major variables except for plant height, to increase; whereas tiller number, leaf area, and leaf and total dry weight increased as seedling number increased. In all plant proportions, higher leaf area index, and leaf and total dry weight was observed for weed than rice. more early growth rates and shorter life cycle were observed for new-introduces than common weed species. Final height, tiller number, leaf area index, leaf maximum dry weight, and total biomass exhibited higher competitiveness for weed than rice. Weeds were superior to rice in all plant proportions except for 1:3 (weed:crop) which were similar in final tiller number; where presence of only one weedy plant in each hill, resulted in equal or mostly higher production compare with three rice plant. These results indicated that new-introduced as well as common weed species possess the high competitive ability against rice.