effect of water depth and temperature on germination characteristics of rice and barnyard grass in the laboratory conditions

response of seed germination of a crop to different environmental conditions is one of the most important determination factors to indicate its ability in competition with weeds. in order to evaluate the effects of water depth and temperature on the germination of different varieties of rice and barnyard grass, an experiment was conducted in the seed laboratory, faculty of agriculture, ferdowsi university of mashhad, as a factorial design based on a complete randomized blocks in four replications of 25 seeds. first factor was water depth in six levels (0, 2, 4, 6, 8, and 10 cm), second factor was temperature in seven levels (10, 15, 20, 25, 30, 35 and 40 oc), and third one was different cultivars (khazar, hashemi and domsiah) and barnyard grass. according to the results the best germination characteristics of all rice varieties and barnyard grass obtained at 30 oc. with increasing temperature up to 30oc germination increased. however, temperatures above 30oc reduced the germination. increasing water depth lead to reduce the speed and percentage of germination in all varieties, but the effect of water depth on the germination of rice varieties was lower than the barnyard grass.