Determination of Critical Period of Weed Control on Soybean in Assosa, Western Ethiopia

Abstract

An experiment was conducted for three years (from 2013 to 2015) to determine the
critical period of weed control (CPWC) in soybean (Glycine max (L.) Merr.) at the
research farm of Assosa Agricultural Research Center in Assosa zone. Western
Ethiopia. CPWC is an estimate of a duration that weed control must be effective to
prevent weed interference from reducing yields or a time interval when it is essential
to maintain a weed free environment to prevent crop yield losses. The study included
two categories of treatments: WFO = weed interference season long (no weed control),
WF15, WF30, WF45, WF60, WF75, WF90 = weed free for 15, 30, 45, 60, 75 and 90
days after crop emergence (DACE), respectively; and WI0 = weed free season long
(no weed infestation), WII5, WI30, WI45, WI60, W175, WI90 = weed interference
for 15, 30, 45, 60, 75, and 90 DACE respectively. Seed yield and yield components of
soybean increased as the weed free period increased, and decreased as the weed
interference period increased. When weeds were allowed to compete with the soybean
for the whole growing season (WFO), the crop yield was reduced by 49.34%
compared to the whole season weed free treatment (WI0). Based on 20 % acceptable
yield loss (A Y L ) value model, results of this study revealed that the CPWC started at
15 DACE and ended at 60 DACE. Therefore, controlling weeds during this period,
possibly two weed removal operations at the beginning and end of the critical period,
is necessary to prevent a significant soybean yield loss.