Competition of barnyardgrass (Echinochloa crus-galli (L.) Beauv.) in direct seeded rice.
Field trials conducted in 1988-89 revealed that, at densities of 15 and 25 plants/m2, barnyard grass significantly reduced the number of tillers of rice cv. MR 71 at maturity. Only 10 plants/m2 were required to cause yield reductions of about 18.7% (i.e. 1 t/ha). Negative relationships between the number of panicles/m2 and rice yield, and between the DW of barnyard grass and rice yield, were established. The number of barnyard grass panicles/m2 was also negatively correlated with the number of rice panicles/m2. The critical period of competition was found to be between 15-30 d after sowing (DAS). Competition with the weed during the first 15 DAS had no significant effect on rice yield, whereas competition beyond 15 DAS caused drastic reductions in rice grain yields. Grain yields of rice increased significantly with the increase in the duration of the weed-free period up to 30 DAS. The density of weeds emerging after 30 DAS was low, and subsequently their growth was suppressed by the crop.