Synergistic Impacts of Seaweed Extracts and Humic Acid Granules on Soil Physicochemical Properties and Crop Productivity: A Review

Seaweed extract and humic acid granules are increasingly recognized as effective biostimulants that help with sustainable soil management and improve crop productivity. Seaweed extract often made from brown macroalgae like Ascophyllum nodosum, Sargassum species and Kappaphycus alvarezii provides bioactive compounds, including phytohormones, polysaccharides, amino acids, and micronutrients. These compounds promote root development, boost stress tolerance, and stimulate important metabolic processes. Humic acid granules improve soil fertility by enhancing soil structure, increasing cation exchange capacity, retaining nutrients better, and supporting beneficial microbial activity. Together, these amendments create synergistic effects that enhance soil properties, such as organic carbon content, moisture retention, and aggregate stability. Their combined use has been proven to increase nutrient uptake, boost chlorophyll synthesis, improve photosynthesis, and strengthen plants’ resistance to abiotic stresses. These advantages lead to higher crop yields by about 15 to 30%, better produce quality, and more efficient use of inputs in field and horticultural crops. The environmental benefits include reducing reliance on synthetic fertilizers, lowering greenhouse gas emissions, and promoting long-term soil health. Economically, using seaweed and humic acid granules offers better benefit-to-cost ratios and encourages the adoption of regenerative and climate-smart farming practices. This review summarizes current scientific evidence on the mechanisms, interactions, and agronomic benefits of these natural amendments, showcasing their importance in sustainable agriculture.