Evaluating the yield and yield components in traditional and improved rice cultivars (Oryza sativa L.) in comparison to yellow nutsedge (Cyperus spp. L)

In an attempt to investigate the effect f nutsedge (Cyperus spp. L.) density on yield and some of the yield components of the traditional and improved rice cultivars of rice, a field experiment was conducted at Agricultural Sciences and Natural Resources University of Sari in 2011. The treatments included four levels of the abovementioned weed (control, 60, 120, and 180 plants per square meter) and three rice cultivars (Tarom, as the traditional cultivar, Shirodi and Ghaem as improved cultivars). The study was carried out in factorial based randomized complete block design with three replications. The results of ANOVA indicated that there was a highly significant difference between weed density, cultivars, and their interaction in terms of fertile tiller number, plant length, filled and unfilled grain number, days remaining to 50% flowering and maturity, 1000 grain weight, panicle length, grain figure, and biological and grain yield. On the basis of the means comparison, the highest amount of plant height (122cm), 1000 grain weight (24.49 g), filled grain number (108 grains per panicle), and panicle length (28 cm) was observed in Tarom. The maximum of days to 50% flowering and maturity (113 and 122 days, respectively), tiller number per hill (23), fertile tiller number, biological and grain yield (1800 and 740 g m-2, respectively) was recorded for Shirodi cultivar in control treatment. The minimum amount of these traits belonged to 180 yellow nutsedge per square meter. The results also indicated that the competitiveness of the rice cultivars was significantly different in various weed densities.. Generally, the results of this experiment indicated that yellow nutsedge had high competitiveness ability even in low density and that an increase in the density of this weed up to 180 plant per square meter significantly and linearly reduced the yield and yield component of rice cultivars. Nevertheless, Tarom cultivar had the best competitive index in different nutsedge density due to its good physiological and morphological parameters.