Determination of Critical Period of Weed-Crop Competition in Rice ( Oryza sativa L.) in Bench Maji and Kaffa Zone, South Western Ethiopia

Abstract

Accurate assessment of crop weed interference period is an essential part for planning an effective weed management for cropping systems and, hence, can be considered the first step to design weed control strategy. The experiment was conducted at Guraferda and Gojeb, Southern Ethiopia during the 2016 main cropping season to assess the critical period of weed-crop competition and yield loss in rice. There were 14 treatments comprising: two series i.e. early (weedy up to 10, 20, 30, 40, 50, 60 and 70 days after crop emergence) and late (weed free up to 10, 20, 30, 40, 50, 60 and 70 days after crop emergence) competition periods were compared with two checks namely complete weed free and weedy check. The treatments were arranged in randomized complete block design with three replications for each set. The major weed species competing vigorously with rice were Cyperus assimilis, Setaria pumila, Phalaris paradoxa and Xanthium spinosum. With increasing duration of weed interference, weed dry weight, and the number of days of rice plant required to reach physiological maturity were increased whereas number of tillers per plant, panicle length, thousand seed weight, grain yield, aboveground biomass, and harvest index of the rice crop were reduced. Uncontrolled weed growth significantly reduced rice grain yield by 68% compared to the grain yield obtained from the weed-free check plots. The beginning and the end of critical period of weed crop competition were based on 5 and 10% acceptable yield loss levels, which were determined by fitting logistic and Gompertz equations to relative yield data, representing increasing duration of weed-interference and weed-free periods. In conclusion, the results of the study revealed that, to reduce the loss in the grain yield of rice by more than 10% and higher economic return, it is important to keep the crop weed-free between 30 to 70 days after crop emergence at Guraferda, in Bench Maji Zone and 28 to 47 days after crop emergence at Gojeb in Keffa Zone.