Competitive Effects of Dwarf Bean Cultivars (Phaseoulus vulgaris L.) on Maize (Zea mays L.) Intercrop Productivity Influenced by Spatial Arrangements

Competitive effects and responses influenced by spatial arrangements and dwarf bean interactions were assessed in traditional maize/bean intercropping systems in northern Malawi at the Meru Experimental Research Station between the 2018/2019 and 2019/2020 growing seasons. A revised maize population with reduced plant spacing as a response to crop intensification limited the inclusion of bean intercrops and, hence, reduced bean productivity. Increasing dwindling landholding per capita aggravated the need to identify suitable bean cultivars for intercropping. Five dwarf bean varieties bred for a sole cropping system were evaluated in four spatial intercropping arrangements with maize at two bean planting densities in a randomised complete block design (RCBD) replicated four times in an additive series. Interactions between companion crops were assessed with the land equivalent ratio (LER) and aggressivity (A). Crop yields were measured to ascertain crop interactions. The PLER showed significantly higher values for maize than bean intercrops. Across the two cropping seasons and at any bean sowing density, alternate-row intercropping showed statistically better land and resource use efficiencies than within-row intercropping. The A values for maize were higher than beans in the intercropping systems. In the intercropping system, maize and beans had positive and negative A values, respectively. In both growing seasons, LER and A values increased in alternate-row over within-row intercropping systems, demonstrating that maize/dwarf bean intercropping has the potential to improve productivity among smallholder farmers in Malawi. All bean cultivars performed well in intercropping arrangements in both seasons except for Mnyambitira, which performed inferiorly in within-row intercropping except for alternate-rows. At any bean sowing density, farmers can realise more benefits if the bean intercrops are spatially sown in alternate-row than within-row arrangements