Common bean (Phaseolus vulgaris) is a leguminous plant that can form a symbiotic relationship with rhizobia in the soil. Rhizobia convert nitrogen in the atmosphere into ammonia, providing nitrogen nutrition for leguminous plants. However, due to the low effectiveness of rhizobia in the soil, common bean has one of the lowest nitrogen fixation efficiencies among food legumes. Some studies have shown that pre-inoculating common bean seeds with elite rhizobial strains can enhance nitrogen fixation, thereby promoting the plant growth of common bean and increasing the grain yield. As one of the most important food legumes in Ethiopia, the grain yield of common bean is quite low, because of the lack of improved cultivars, and the fact that most farmers neither use Rhizobium inoculation nor apply mineral fertilizers at the recommended rate, resulting in low nitrogen and phosphorus content in the farmland soil. Meanwhile, in Ethiopia, the low availability of phosphorus is the main factor limiting the grain yield of common bean. So, can the combination use of Rhizobium inoculation and low phosphorus application increase the yield of common bean?
Felix D. DAKORA, academician and president of the African Academy of Sciences, foreign academician of the Chinese Academy of Engineering, and professor at the Tshwane University of Technology, has long been deeply involved in the research of biological nitrogen fixation mechanisms and related application technologies. In order to study the above question, professor DAKORA and his colleague Dr. Tarekegn Y. SAMAGO selected two common bean cultivars in Ethiopia (Hawassa Dume and Ibbado), which have high yield potential, as the research objects. They chose two high-quality rhizobial strains (HB-429 and GT-9), and set different levels of phosphate fertilizer to study the plant growth, nodulation and grain yield of common bean inoculated with rhizobia under different levels of phosphorus treatment.
The results showed that, relative to the uninoculated control, the two bean cultivars responded strongly to Rhizobium inoculation, with strain HB-429 outperforming strain GT-9 in both 2012 and 2013. Shoot biomass, nodule number and nodule dry matter per plant were increased by 9%, 40%, and 54%, respectively, in 2012, and by 20%, 39%, and 13% in 2013 with strain HB-429 inoculation. This resulted in increased pod number per plant, seed number per pod and grain yield by 56%, 51%, and 49% in 2012, and by 38%, 25%, and 69% in 2013, respectively, with strain HB-429 inoculation. Bean inoculation with GT-9 also increased grain yield by 35% and 68% in 2012 and 2013, respectively.
In addition, the application of phosphate fertilizer to common bean cultivars also had a significant effect. Applying 10–30 kg·ha⁻¹ P to bean cultivars increased shoot biomass, nodule number, and nodule dry matter per plant by 7%–39%, 23%–59%, and 59%–144% in 2012, respectively, and by 10%–40%, 21%–43%, and 12%–35% in 2013, respectively. Relative to the zero-P control, adding only 10 kg·ha⁻¹ P increased pod number per plant, seed number per pod, and grain yield by 10%, 30%, and 61% in 2012, and by 11%, 11%, and 38% in 2013, respectively.
This study found that bean inoculation with Rhizobium alone or in combination with P application, can increase grain yield of the two common bean cultivars. This indicates that recommending these agronomic inputs for use by resource-poor farmers in Ethiopia will be very helpful to increase the local common bean yield. Compared with the Ibbado, Hawassa Dume has a higher yield. Therefore, Hawassa Dume could be recommended for adoption by farmers in combination with the Rhizobium inoculant strain HB-429 and P at 20 kg·ha⁻¹ P in Ethiopia.
This study has been published on the journal of Frontiers of Agricultural Science and Engineering in 2025, 12(1): 104–116. DOI: 10.15302/J-FASE-2024556.