The effect of planting date on weed density, biomass and seed yield in common bean (Phaseolus vulgalris L.) in the semi-arid region of Nyagatare, Rwanda

Bernard Byiringiro, Scovia Birungi, Augustine Musoni, Arnold Mashingaidze

Abstract


Increasing variability in the start and end of the season, with climate change, is presenting a dilemma to farmers on the optimum planting dates for bush beans in semi-arid areas. A study to investigate the effect of planting date on bean yield and weed pressure was conducted at Nyagatare, Rwanda, during the 2009/10 and 2011/12 seasons. The highest seed yield and weed density were recorded at the second planting date in the wet 2009/10 season. Seed yield and weed density were significantly (P<0.001) lower at the first and third planting dates in the wet 2009/10 season. In the dry 2011/12 season, seed yield was highest at the earliest planting date and significantly (P<0.001) decreased ten times with each 15 day delay in planting. There was a significant linear correlation between days delay in planting and weed density (r = 0.99, P<0.001), bean plant dry weight (r = -0.97, P<0.01) and monthly rainfall (r = -0.97, P<0.01) in the dry 2011/12 season. These results suggest that early planting may be detrimental to bean seed yield in long wet seasons, most likely due to intermittent water logging and pre-disposition of the beans to higher disease and pest pressure. Bean seed yield declined as planting was delayed in a short dry season because the beans increasingly matured during dry hot conditions when the rainy season had ended and weed pressure increased as planting was delayed.

Keywords


Common bean, planting date, bean seed yield, weed density, weed biomass

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