Yield response of field-grown cowpea (Vigna unguiculata (L.) Walp.) varieties to Bradyrhizobium inoculation

Common bean (Phaseolus vulgaris L.) is one of the most important and widely cultivated pulse crops in most developing countries. However, its cultivation is globally constrained mainly by low soil fertility and lack of improved agronomic practices. A field experiment was conducted at Hawassa University College of Agriculture, Hawassa Southern Ethiopia to determine the effect of N fertilization and Rhizobium phaseoli strain HB-429 inoculation on growth, nodulation, yield and yield components of common bean variety Hawassa Dume. The experiment was laid out as a randomized complete block design with three replications. Results showed significant increase in growth, nodulation, yield and yield components in plants inoculated with Rhizobium strain HB-429 over the control. Thus, from the results of this study, it can be concluded that Rhizobium inoculation with strain HB-429 is the best performing treatment to be recommended for profitable grain yield of common bean at the Hawassa and other similar areas.

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Supplying nitrogen to crops through selecting high N fixing legumes and effective inoculant is one of the key strategies to improve crop productivity. However, studies related to the effect of Bradyrhizobial inoculation on leaf growth, its functioning in relation to photosynthesis, and transpiration efficiency (WUE) of cowpea [ Vigna unguiculata (L.) Walp] varieties in the tropics were inadequate. A two-year field experiment was conducted at three sites to evaluate the effect of inoculation on leaf growth, gas exchanges and photosynthetic efficiency of cowpea varieties. The study treatments were composed of four varieties, Keti (IT99K-1122), TVU, Black eye bean, and White wonderer trailing and three levels of inoculation (non-inoculated or inoculated with Bradyrhizobium strains CP-24 or CP-37). Gas exchange was measured on live plants at 67–77 days after sowing, between 8:00 to 11:00 a.m. and 14:00 to 16:00 p.m. Leaf growth parameters (leaf number and leaf area) were measured by destructive sampling, and the yield data was determined by harvesting plants in the three central rows at physiological maturity. Variety TVU performed best in terms of leaf number, photosynthesis rate, and WUE. Whereas, Black eye bean revealed superior performances for leaf area, leaf area index, and stomatal conductance compared with the rest two varieties. The effect of inoculation was significant with 14.0, 23.8, 13.7, and 11.0% advantage in leaf area, leaf area index, net photosynthesis, and WUE, respectively. Moreover, the performance of cowpea of the 2018 cropping season showed a relative advantage over 2019 in terms of leaf number, leaf area, leaf area index, net photosynthesis, and stomatal conductance. Therefore, inoculating cowpea varieties with effective Bradyrhizobium strain can be a viable alternative to enhance growth, gas exchange, photosynthetic efficiency, and grain yield.

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Chemical phosphatic fertilizers are mainly produced from phosphate rocks, a natural reserve that is depleting rapidly. These chemical phosphatic fertilizers are polluting the environment at an alarming rate as a result of injudicious application to farmlands. On the other hand, phosphate-solubilizing biofertilizers (PSBs) are often considered better alternatives to industrial phosphatic fertilizers in many ways. PSBs are microorganisms capable of solubilizing insoluble forms of phosphate into soluble plant-usable forms. This paper is written with the objective of discussing the impacts of phosphatic fertilizers and making the case for why we should shift to PSBs instead. Phosphatic fertilizers have numerous impacts on the environment (water bodies, land resources, and air), and micro- and macro-organisms, including humans. Chemical fertilizers also tend to be more expensive, especially for farmers in developing countries. On the contrary, PSBs tend to be safer and way more beneficial than their chemical counterparts in that they are environmentally friendly and cheaper options of availing plant-usable phosphorus. PSBs are also involved in other beneficial roles such as the production of phytohormones and secretion of anti-phytopathogenic metabolites. The phytohormones enhance plant growth and the metabolites render crops immunity against phytopathogens. Hence, it is vital to replace chemical phosphatic fertilizers with PSB inoculants both to prevent the irreversible impacts of chemical fertilizers and to take advantage of the numerous benefits of PSBs. Moreover, it does not seem as if there is an option given the fact that the global phosphate reserve is depleting and the impact of fertilizer on the environment is worsening as time goes by.

Cowpea (Vigna unguiculata L. Walp) has a major role in daily diet of the rural community and poor urban population, serving as a source of energy, protein and minerals, in developing countries. Its straw used for animal feed, and the crop also improves soil fertility by fixing the atmospheric nitrogen. However, its productivity is constrained by lack of improved varieties and poor agronomic practices. A field experiment was conducted at Ziway, central rift valley of Ethiopia, to evaluate the response of cowpea varieties to Bradyrhizobia inoculation. The treatment consisted of four Bradyrhizobia strains (control, GN-100, GN-102 and MB-140) and five cowpea varieties (Bole, Black eye-bean, TVU1977.0D1, Assebot and White Wonder). The experiment was carried out using a randomized complete block design with three replications. The results revealed marked varietal differences in plant growth, nodulation, yield and yield components. Of the five cowpea varieties studied, Black eye-bean generally showed superior performance in most measured parameters. Bradyrhizobium inoculation significantly (p≤0.05) increased plant growth, nodulation, yield and yield components. The interaction effect of variety and Bradyrhizobium caused significant variations in the number of nodules, number of seeds, hundred seed weight and seed yield. The highest grain yield was recorded from Black eye-bean variety (3.08 t/ha) and Bradyrhizobium strain GN-102 (3.11 t/ha) inoculation. It could, thus, be deduced that the use of strain GN-102 and variety Black-eye bean markedly increases the productivity of the crop in the region.