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Common bean is an important food and cash crop in eastern Ethiopia. However, its yield is constrained by weeds. Therefore, this study was conducted in 2012 main cropping season at Haramaya and Hirna research fields, eastern Ethiopia, to determine the effect of plant spacing and weeding frequency on weeds, yield components and yield of common bean. The experiment comprised 18 treatment combinations with three inter- and intra-row plant spacing, respectively, (30 cm × 10 cm, 30 cm × 15 cm, 40 cm × 10 cm) and six weeding frequencies (one weeding by handhoeing two weeks after crop emergence, one weeding by hand-hoeing three weeks after crop emergence, one weeding by hand-hoeing four weeks after crop emergence, two weeding by handhoeing two and five weeks after crop emergence, weed-free check, weedy check). The experiment was laid out as a randomized complete block design (RCBD) in a factorial arrangement and replicated three times per treatment. It was observed that broad-leaved weed species were dominant at both sites with relative density of 61.2 and 73.2% at Haramaya and Hirna, respectively. Interaction of sites, plant spacing and weeding frequencies significantly affected weed density and dry weight. Days to flowering, days to physiological maturity, plant height, number of pods per plant, number of seeds per pod, hundred seed weight, grain yield, aboveground dry biomass, and harvest index significantly affected by weeding frequencies. Combination of plant spacing of 30 cm x 10 cm and two weeding by hand-hoeing two and five weeks after crop emergence significantly reduced the weed dry weight by 95.3 and 95.8% at Haramaya and Hirna, respectively, as compared to the same plant spacing with no weeding throughout the season. Common bean plants weeded by hand-hoeing twice two and five weeks after crop emergence flowered significantly earlier next to plants kept weed-free. Significantly higher number of pods per plant, grain yield (2984.0 kg ha-1) and aboveground dry biomass were obtained at Hirna than at Haramaya. However, significantly, higher numbers of seeds per pod and harvest index were obtained at Haramaya than at Hirna. Significantly higher grain yield (2612.2 kg ha-1) and (2718.8 kg ha-1) were obtained from one weeding by hand-hoeing two weeks after crop emergence and two weeding by hand-hoeing two and five weeks after crop emergence next to weedfree check, respectively. However, the economic analysis revealed that the highest net benefit of 15924 ETB ha-1 was obtained in response to combining the spacing of 30 cm × 10 cm with twice weeding by hand-hoeing two and five weeks after crop emergence. It could be concluded that planting common bean plants at the spacing of 30 cm between rows and 10 cm between plants and weeding the crop by hand-hoeing twice at two and five weeks after crop emergence resulted in optimum growth and grain yield of the crop.
Keywords: Grain Yield; Hand-hoeing; Harvest Index; Net Benefit; Weed; Weed Dry Weight