Enhancing soil health and crop growth using seaweed extracts of Gracilaria species in pulp and paper industry effluent-irrigated soil

Large amounts of toxic effluents that negatively impact soil health and plant development are released by the pulp and paper industry, making it a major worldwide polluter. To improve crop growth and reduce abiotic stress in soil irrigated with papermill effluents, this pot culture study explores the potential of seaweed extracts from Gracilaria gracilis and Gracilaria edulis as biostimulants. Recommended Dose of Fertilizer (RDF) was applied to soil samples together with different concentrations of seaweed extracts (2.5 %, 5.0 %, 7.5 % and 10 %). The parameters evaluated were soil pH, electrical conductivity, nutrient availability, enzyme activity, plant development metrics and the amount of carotenoid and chlorophyll. The findings showed a notable increase in soil fertility. The application of Gracilaria extracts increased the availability of nutrients, especially nitrogen (up to 145.55 kg/ha in T4 (Gracilaria sp. 1 @ 7.5 % + RDF), phosphorus (up to 28.0 ppm in T4 (Gracilaria sp. 1 @ 7.5 % + RDF) and potassium (up to 143.5 ppm in T4 (Gracilaria sp. 1 @ 7.5 % + RDF) and lowering the pH of the soil (from 7.89 to 6.11). Significant improvement was observed in urease, phosphatase and dehydrogenase enzymatic activity. Concerning plant performance, 7.5 % Gracilaria extract produced the greatest results (T4 (Gracilaria sp. 1 @ 7.5 % + RDF) and T8 (Gracilaria sp. 2 @ 7.5 % + RDF). The height of Maize plants (up to 204.3 cm in T8 (Gracilaria sp. 2 @ 7.5 % + RDF), the number of leaves (12 in T4 (Gracilaria sp. 1 @ 7.5 % + RDF) and T8 (Gracilaria sp. 2 @ 7.5 % + RDF) and the amount of chlorophyll (3.10 mg g-1 in T10) increased. With a high carotenoid level of 0.86 mg/g in T10 (Gracilaria sp. 1 @ 7.5 % + Gracilaria sp. 2 @ 7.5 % + RDF), photosynthetic efficiency and stress tolerance were 10-15 % improved. According to the studys’ findings, seaweed-based biostimulants, particularly at concentrations of 7.5 % seaweed extract from two species, offer an environmentally acceptable approach to mitigating abiotic stress, enhancing soil health and promoting crop growth in polluted areas. Using Gracilaria extracts in sustainable farming methods is suitable for alleviating environmental stress.