International Journal of Plant & Soil Science

Modern agriculture requires approaches that sustain crop productivity while reducing environmental burdens associated with intensive synthetic inputs. This review examines microalgae as multifunctional biological resources for sustainable agriculture, with emphasis on their roles as biofertilisers, biostimulants, biopesticides, soil amendments, and agents of bioremediation. Microalgal and cyanobacterial biomass can contribute to nutrient availability through biological nitrogen fixation, phosphorus and potassium mobilisation, and the delivery of macro- and micronutrients. Their metabolites, including phytohormones, polysaccharides, amino acids, vitamins, and antioxidant compounds, can support plant growth and stress responses. Microalgae also produce bioactive substances with potential applications in disease, insect, nematode, and weed management. In soils, microalgal biomass and exopolysaccharides can support aggregation, moisture retention, organic carbon inputs, and microbial activity, while microalgae-derived biochar provides an additional soil-amendment option. Microalgal systems may also assist in the removal of nutrients, heavy metals, and selected organic pollutants from contaminated soils and agricultural wastewater, with treated effluents and residual biomass offering opportunities for resource recycling. Open raceway ponds and closed photobioreactors provide contrasting production options, although large-scale cultivation costs, formulation stability, and variable field performance remain important constraints. Overall, the reviewed evidence supports the integration of microalgal technologies within circular agricultural systems, while further work is needed to improve production efficiency, application consistency, and practical scalability.