Duration on some The Effect of Weed Interference Morphologic Traits and Yield of Onion (Allium cepa L.)

To determine the effect of weed interference duration on morphological traits and yield of onion (Allium cepa L.), variety Ghermez Azarshahr, an experiment was carried out in an randomized complete block design in three replications at Agricultural Research Farm of Faculty of Agriculture, University of Tabriz in 2010. In this experiment, twelve treatments consisted of six initial weed-free periods in which plots were kept free of weeds for 0, 20, 40, 60, 80 and 100 days after crop emergence (DAE), and then weeds were allowed to grow until harvest. Six initial weed-infested periods in which, weeds were allowed to grow for 0, 20, 40, 60, 80 and 100 DAE, after which the plots were kept free of weeds until harvest. The effect of weed interference on plant height, leaves per plant, average diameter of bulb, biomass per plant, yield per plant and yield per unit of area was significant. All traits of the onion were reduced as the weed infested period was increased. Increasing the weed infested period more than 40 DAE, reduced significantly the plant height, leaves number per plant and bulb diameter of onion. Increasing the weed-infested period to 100 DAE, reduced the onion bulb yield per plant and per unit area in comparison with full weed-free treatment by 95 and 96%, respectively. Also increasing the weed free period up to 40 DAE had no significant effect on bulb yield per plant and per unit of area. Generally results indicated that in order to prevent bulb yield loss in onion, the weed control was essential from onion emergence to 100 DAE and after this period, the weed control or its presence did not affect onion yield.