Shade avoidance and the yield-density response in two navy bean (Phaseolus vulgaris L.) varieties under weed-free and weedy conditions

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Koroscil, Leanne Justina
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Field bean (Phaseolus vulgaris L.) production in Canada is limited to few regions, mainly Manitoba and Ontario. For being one of the main producers of field bean in Canada, Manitoba research has been limited in comparison to other major crops grown in the region. Few effective herbicides are registered in field bean and other methods of weed control must be used to enhance crop protection. This study was conducted to enhance the knowledge around the effect of spatial arrangement on field bean development and seed yield, which can simultaneously be used as an Integrated Weed Management (IWM) strategy against weed competition. The specific strategies examined were planting densities, planting date, and cultivar selection. The premise of the study focused on aspects of previous research conducted by Schmidt (2020) based out of the University of Manitoba, which were not found to conform to the ‘law of constant final yield’ (LCFY), an occurrence theorized by Weiner and Freckleton (2010) wherein at low plant densities crop yield is directly dependent on plant density while at increased densities, crop yield forms a plateau and becomes independent of plant density. This was not apparent in the navy bean experiments conducted by Schmidt (2020). To further examine this, two experiments were established at Carman, Manitoba in 2017 and 2018 at an early and a late seeding date with two navy bean cultivars, T9905 and Envoy, in each experiment. One experiment was kept weed-free, and the other included weed interference. Field bean seed yields in the weed-free experiment were greater at increased planting densities. Increasing planting densities in the weed-free experiment also enhanced certain shade avoidance characteristics, creating thinner stems, reduced branch numbers, longer first internodes and increased pod clearance. Interestingly, plant height did not significantly change with increasing planting densities in the weed-free experiment. Increasing planting densities did little to reduce weed biomass in all weedy experiments but one, late-seeded Envoy in 2018. Additionally, the increase in plant density did not improve seed yield outcome against weed competition when the natural weed community was allowed to interfere with the beans for the entire growing season. Over both experiments, the T9905 Type II navy bean cultivar experienced better seed yield results than the Envoy Type I navy bean cultivar.
Manitoba, Field bean, Shade avoidance