Effect of Redroot Pigweed (Amaranthus retroflexus L.) and Barnyard Grass (Echinochloa crus-galli (L.) P. Beauv) Interference on Yield and Essential Oil of Fennel (Foeniculum vulgare Mill.)

Weed infestation in arable lands is much more than one species. Thus, it is important to pay attention to the interaction of multy species of weeds. To study the effect of redroot pigweed (Amaranthus retroflexus L.) and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv) interference on yield and essential oil of fennel (Foeniculum vulgare Mill.), an experiment has been done in Research field of Sari Agricultural Sciences and Natural Resources University during 2017. It has been arranged in a factorial arrangement based on randomized complete block design with three replications with the experimental factors being three densities of redroot pigweed (0, 4, and 8 plants m-2) and three densities of barnyardgrass (0, 4, and 8 plants m-2). The highest grain yield (2230 kg ha-1) and essential oil content (2 %) are obtained at weed free plots. The density of 8 redroot pigweed plants m-2 at simultaneous interference with 0, 4, and 8 barnyard grass m-2 reduce grain yield by 30.1%, 62.9%, and 75.7%, and essential oil content by 24.5%, 26.2%, and 29.5%, respectively, compared with weed free plots. The coefficient of redroot pigweed competitivity is predicted to be higher than barnyardgrass, and the interference of 14.5 barnyardgrass plants m-2 or 7.7 redroot pigweed plants m-2 decreases fennel grain yield by 50%.