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Legumes improve soil fertility through the symbiotic association with microorganisms, such as rhizobia, which fix the atmospheric nitrogen and make nitrogen available to the host and other crops by a process known as biological nitrogen fixation (BNF). Legumes included in the cropping system improve the fertility of the soil and the yield of crops. The advantages of legumes in the cropping system are explained in terms of direct nitrogen transfer, residual fixed nitrogen, nutrient availability and uptake, effect on soil properties, breaking of pests' cycles, and enhancement of other soil microbial activity. The best benefits from the legumes and BNF system can be utilized by integrating them into cropping systems. The most common practices to integrate legumes and their associated BNF into agricultural systems are crop rotation, simultaneous intercropping, improved fallows, green manuring, and alley cropping. However, the level of utilizing nitrogen fixation requires improvement of the systems, such as selecting appropriate legume genotypes, inoculation with effective rhizobia, and the use of appropriate agronomic practices and cropping systems. Therefore, using legumes at their maximum genetic potential, inoculation of legumes with compatible rhizobia, and using appropriate agronomic practices and cropping systems are very important for increasing food production. Importantly, the utilization of legumes as an integral component of agricultural practice in promoting agricultural productivity has gained more traction in meeting the demand of food production of the world populace. Priority should, thus, be given to value the process of BNF through more sustainable technologies and expansion of knowledge to the system.

The rate of growth of the global population poses a risk to food security, demanding an increase in food production. Much of the world's cultivable soils also do not have ideal farming conditions such as soil health and fertility problem and increased pest attacks, which are challenges of food production. In this perspective, there is a need to increase agricultural production using a more economically and environmentally sustainable approach. As practices of agricultural production and improvement, rhizobial inoculants represent a practically effective, ecologically safe, and economically alternative means of realizing maximum agricultural production. This review addressed how rhizobial inoculation advances agricultural production through improving plant growth, nutrient availability and uptake, and yields by enhancing bio-fixation of atmospheric nitrogen and solubilization of soil nutrients. Besides, rhizobial inoculants offer biocontrol of plant diseases by providing resistance against disease-causing pathogens or suppression of diseases. Mechanisms involved in biocontrol of plant diseases include competition for infection sites and nutrients, activation of induced systemic resistance, and production of substances such as growth hormones, antibiotics, enzymes, siderophores, hydrogen cyanide, and exo-polysaccharides. Consequently, this approach is promising as sustainable agricultural practices have yet to supplement or replace chemical fertilizers, serving as a basis for future research on sustainable agricultural production. Despite the multifunctional benefits of rhizobial inoculation, there is a variation in the implementation of this practice by farmers. Therefore, researchers should work on eradicating farmers' constraints in using rhizobia, and future studies should be concentrated toward the methods of improving inoculant quality and promotion of the technology.

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Accelerating agricultural growth remains one of the most urgent goal of Ethiopia as the agricultural sector is the backbone of the Ethiopian economy. The adoption of new agricultural technologies and improved practices are particularly important in increasing agricultural production. This comprises strengthening legumes adoption and production as it contributes to better food security and more sustainable farming systems. Grain legumes are necessary elements of crop production in Ethiopia. The adoption and use of legume crops have been advocated for enhanced nutrition and preserving soil resources. Different improved varieties and legume production technologies have been made available to farmers through various sectors and projects in the country. Various policy measures and initiatives have also been made in improving the adoption, technology generation and contribution of legumes to the various system. Despite their contribution and considerable initiatives, over-all level of adoption and use of legume production is still low. A wide array of technical, economic, social, and institutional factors has been found to encounter the adoption, use and production of legumes along with their value-chain. However, there are still various opportunities that different grain legumes are to be adopted and promoted to increase production and productivity. Essential interventions, innovative approaches, increased production packages and improved technologies and market access should be emphasized and integrated to strengthen grain legumes adoption and production.

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Enumeration of the native rhizobia population is important to determine the abundance of rhizobia in the soil and the achievement of inoculation. In Ethiopia, limited information is available on the population abundance of cowpea nodulating rhizobia. This study aimed to evaluate the population abundance of rhizobia nodulating cowpea and their relation with cropping history and soil properties in cowpea producing areas of Ethiopia. The abundance of rhizobia existing in the soils was assessed by the most probable number technique. The study revealed that the population abundance of rhizobia nodulating cowpea is high, ranging from 3.1 × 10 4 to 1.0 × 10 7 rhizobia cells g −1 of soil, and the population varied at each location. Besides, there was no statistically significant correlation between soil physicochemical properties and the rhizobial population. All the investigated soils had been cropped with cowpea in monoculture (sole cowpea), intercropping (mostly with sorghum and maize) and crop rotation for many years. Thus, the higher rhizobia population observed in this study is associated with the season factor and cropping history of the areas. In general, the soils of cowpea production areas in Ethiopia harbor adequate levels of rhizobia capable of nodulating cowpea, which are passable to provide satisfactory nitrogen fixation and nodulation.