Re-visiting potential benefits of microbial inoculants in agriculture: Opportunities and challenges

There is a growing understanding of the interdependence between plants and the soil microbiome, driving global efforts to develop sustainable agricultural solutions that enhance nutrient supply and resilience against biotic and abiotic stresses. In parallel, there is considerable interest in the use of microbial inoculants in agriculture based on advanced understanding of the role soil microorganisms play in supporting plant nutrient acquisition, control of soil pathogens, and rehabilitation of degraded soil. The number of commercially available microbial inoculants has increased markedly over the last 20 years, yet inconsistent plant-related benefits under field conditions have limited the widespread adoption of these emerging products. Research on symbiotic nitrogen fixation with legumes, interactions between plants and mycorrhizal fungi, and plant growth promoting rhizobacteria (PGPRs) have laid the foundation for the majority of commercial microbial inoculant products available today. The next-generation of inoculant products will employ advanced strategies including -omics and cutting-edge sequencing tools to understand the complexity of the soil microbiome, its interactions with plants, and role in providing ecosystem functional services. Furthermore, co-application of organic amendments with microbial inoculants has shown promise in enhancing growth-promoting effects. Drawing on knowledge of the intricacy of interactions between core soil microbial groups and roots, the interest in developing synthetic community-based inoculants is rapidly expanding. Additionally, some inoculants may improve soil aggregation and overcome water-repellence, providing further protection against environmental stresses. However, considerable attention is needed to address ecological and practical complexities that hinder successful field application with both current and next-generation inoculants.