Molecular Microbiology Research 2024, Vol.14, No.2, 109-118 http://microbescipublisher.com/index.php/mmr 114 2018; Bellabarba et al., 2019). The complex interplay between rhizobia and other soil microorganisms underscores the importance of a holistic approach to understanding soil health and fertility. The ability of rhizobia to coexist and cooperate with other microbes highlights their role in maintaining a balanced and productive soil ecosystem (Masson-Boivin and Sachs, 2018; Sachs et al., 2018). 6 Agricultural Applications and Practices 6.1 Inoculant development and use The development and use of rhizobial inoculants have shown significant promise in enhancing legume growth and soil fertility. Rhizobia, as plant growth-promoting bacteria, form symbiotic relationships with legumes, facilitating nitrogen fixation, which is crucial for plant nutrition and soil health. The effectiveness of rhizobial inoculants has been demonstrated in various studies. For instance, specific rhizobium strains have been shown to significantly enhance nodulation, nitrogen fixation, and nutrient uptake in Vicia faba, leading to improved soil nitrogen balance (Allito et al., 2020). Additionally, novel rhizobial strains have been identified that exhibit superior nodulation and nitrogen fixation even under high nitrate concentrations, making them promising candidates for use in nitrate-applied soils (Nguyen et al., 2019). The use of rhizobial inoculants not only boosts legume productivity but also contributes to sustainable agricultural practices by reducing the need for chemical fertilizers (Masson-Boivin and Sachs, 2018; Mabrouk et al., 2018). Additionally, several novel rhizobial strains have been identified that maintain excellent nodulation and nitrogen-fixing capabilities even under high nitrate concentrations, making them promising candidates for use in soils with nitrate application (Nguyen et al., 2019). Research has shown that the traditional rhizobial strain Bradyrhizobium diazoefficiens USDA110 exhibits significantly reduced nodulation ability at higher nitrate concentrations, whereas several newly isolated rhizobial strains (NKS4, NKM2, and NKTG2) can still effectively form nitrogen-fixing nodules at a nitrate concentration of 20 mM (Figure 2). Comparisons of nodulation efficiency, nitrogen-fixing activity, and competitiveness reveal that these new strains exhibit superior nodulation capabilities and growth characteristics compared to USDA110. The study also found that the new strains can enhance the expression of symbiotic signaling genes in soybeans and reduce the expression of nitrate-dependent nodulation repression genes. The discovery of these new strains offers potential microbial inoculant options for improving soybean production under high nitrogen fertilizer conditions. The use of rhizobial inoculants not only increases the productivity of leguminous crops but also promotes sustainable agricultural practices by reducing the need for chemical fertilizers (Masson-Boivin and Sachs, 2018; Mabrouk et al., 2018). 6.2 Crop rotation and intercropping Crop rotation and intercropping are traditional agricultural practices that can be optimized through the use of rhizobia to enhance soil fertility and crop yields. Intercropping, in particular, has been shown to maximize the use of resources and improve nitrogen utilization. A meta-analysis of grain legume-cereal intercropping revealed that intercropping increases the proportion of nitrogen derived from nitrogen fixation in legumes and enhances soil nitrogen acquisition in cereals (Rodriguez et al., 2020). This practice not only improves the overall nitrogen balance in the soil but also reduces the need for external nitrogen inputs, thereby promoting sustainable agriculture. Furthermore, intercropping systems involving rhizobial inoculation, such as maize/faba bean intercropping, have demonstrated increased productivity and nitrogen fixation, along with reduced nitrogen losses, especially in challenging environments like reclaimed desert soils (Mei et al., 2021). 6.3 Sustainable agriculture practices Sustainable agriculture practices aim to maintain high productivity while minimizing environmental impact. The use of rhizobia in sustainable agriculture is a key strategy to achieve this balance. Rhizobia enhance plant growth and resilience by fixing atmospheric nitrogen, solubilizing phosphates, and producing phytohormones, which collectively improve plant nutrition and defense mechanisms (Mabrouk et al., 2018). Rhizobia can tolerate various abiotic stresses, such as extreme temperatures, pH, salinity, and drought, making them valuable in diverse agroecosystems. The integration of rhizobia into sustainable agricultural practices, such as the use of biofertilizers and biopesticides, can lead to healthier and more productive farming systems.
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