Determination of the best weeds control period in a soybean (Glycine max) new released hybrid: Williams.
In order to determine the critical period of weeds control in soybean in semi-arid regions two experiments were conducted at Tabriz, Iran, on soybean hybrid Williams, based on randomized complete block design. For weed-infested plots, weeds were hand removed after 20, 40 and 60 days after emergence (DAE) and were kept weed free thereafter. For weed-free plots, weeds were allowed to compete with crop plants from 20, 40 and 60 DAE thereafter. Weeds interference duration of 40 DAE or more and weed-free period of less than 40 DAE greatly reduced the number of pod bearing branches per plant. Significant reduction in soybean yield up to 50% with increasing of weeds interference duration indicates that weeds is highly competitive with crop, and their competition beyond 40 WAE, results in greater crop yield loss than 24%, compared to control. A Gompertz model provided the best fit for the maximum weed-infested experiment. The relationship of crop yield with weed-free period was best described by the Logistic equation. The best weeds control period in soybean field using 5% permissible yield loss was between 40-60 DAE.