Challenges and opportunities in the use of microbial inoculants in hydroponic crops: A literature review

Abstract

The use of microbial inoculants in hydroponic crops has emerged as an innovative strategy to enhance plant performance, reduce dependence on chemical fertilizers by up to 80 %, and increase the sustainability of soilless agricultural systems. This literature review covers studies published between 2015 and 2025 and aims to identify the main challenges and opportunities associated with the application of microbial inoculants under hydroponic conditions. Based on the analysis of recent studies, key opportunities are identified, such as improved nutrient absorption, stimulation of biomass and photosynthesis, greater tolerance to abiotic stressors (e.g., salinity, drought or iron deficiency), and reduced nitrate accumulation in plant tissues, thereby lowering health risks and environmental impacts such as water eutrophication. Additionally, the potential of microbial co-inoculations and mixed formulations is highlighted as a viable alternative to enhance the growth and nutritional quality of crops such as lettuce, arugula, basil, and saffron, as they are often more effective than single inoculations, although this depends on the type of microorganisms and the crop. The main technical and methodological challenges identified include variability of results across species and systems, the lack of standardized protocols for formulation and application, negative effects from undesired interactions with inputs or native microbiota, and limited stability under variable environmental conditions. In addition, regulatory barriers related to the registration, validation, and large-scale adoption of these biological inputs further restrict their effectiveness and commercial integration. Moreover, there is a recognized need to investigate the molecular mechanisms involved, such as phytohormone production, nitrogen fixation, phosphate solubilization, activation of plant antioxidant pathways and optimize application protocols. This review concludes that although the path toward sustainable hydroponics with microbial inoculants still faces obstacles, it represents a promising strategy to improve the efficiency, sustainability, and quality of intensive agricultural systems.