Microalgae-Based Strategies for Soil Health and Crop Productivity: Mechanisms, Challenges, and Pathways to Climate-Resilient Agriculture

Microalgae hold significant potential as nature-based solutions in agriculture, offering benefits such as nitrogen fixation, enhanced nutrient cycling, stimulation of beneficial microbes, strengthening soil structure, and carbon sequestration. Yet, despite their potential, the role of microalgae, particularly through their interactions with soil systems, remains largely underexplored. Their ability to generate bioactive substances such as phytohormones, amino acids, and extracellular polymeric substances (EPS) fosters soil aggregation, nutrient availability, water retention, biological soil crust, and soil restoration, which ultimately supports plant growth and productivity. Moreover, the thermochemical conversion of microalgal biomass into biochar offers an effective strategy to improve carbon sequestration while simultaneously enriching soil nutrient content, thereby increasing crop productivity. While microalgae-based products often demonstrate strong efficacy under laboratory and greenhouse conditions, their performance in the field remains constrained by soil physicochemical properties, ecological incompatibility, competition with native microbial communities, and environmental variability, leading to inconsistent outcomes and highlighting the need for soil-specific, field-relevant strategies. Furthermore, the lack of standardized and cost-effective cultivation, formulation, and processing, along with low biomass yield and energy-intensive production, continues to limit their large-scale adoption in agricultural systems. Therefore, this narrative review aimed to discuss the mechanisms of coupling microalgal biomass and biochar to enhance soil health and crop growth, while also addressing field-performance constraints. It provides a balanced view of the potential and challenges of microalgae-based technologies for sustainable soil management and crop productivity. Overall, microalgae possess significant potential to improve soil health, increase crop yields, and contribute to sustainable agriculture that can withstand climate challenges.