Competitive effects of Echinochloa crus-galli and Monochoria vaginalis in tropical irrigated rice.
A regression model was constructed from the results of competition studies, conducted over 3 years on >1500 4 m2 plots in Cikampek on the Indonesian island of W. Java, between rice (mainly the transplanted cv. IR-36) and Echinochloa crus-galli or Monochoria vaginalis (both weeds sown 2-3 d before rice and thinned to the required density after 7-14 d). The av. rice yield losses due to competition from E. crus-galli and M. vaginalis were estimated from the model to be 110 and 2 kg/ha, resp., provided that the weed densities were below 300 or 20 plants/m2, resp. Field observations of the effects of rice density and variety and fertilizer concn on weed threshold levels verified the estimated values and indicated their variability.