Seaweed extract as a biostimulant for improving root growth and soil health in wetland rice cultivation

Wetland acid soils have low biological activity and nutrient imbalances, which calls for sustainable methods to enhance the biological health of the soil. However, there is few comparative data regarding the way various biostimulants affect rice phenolic acid responses, root micro-morphology and soil biological functioning in wetland acid soil. Therefore, a pot culture experiment was conducted at the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, Thiruvananthapuram, to evaluate the influence of biostimulants on soil biological properties in a wetland ecosystem using the rice variety ‘Uma’. The study followed a completely randomised design (CRD) with 10 treatments and 3 replications comprising different biostimulant treatments applied along with the recommended dose of fertiliser (RDF) and absolute control. Among the treatments, RDF + Seaweed extract recorded the highest catalase activity (9.21 mg H2O2 g-1 soil h-1), significantly higher than all other treatments and dehydrogenase activity was also improved. The seaweed extract treatments also had a major impact on the enzyme activity number (EAN), an integrated indication of overall soil enzymatic performance. Scanning electron microscope (SEM) images of rice roots from soil treated with seaweed extract, captured at 750× magnifications, revealed significant improvements in root morphology and microbial colonisation. The seaweed extract treatment also enhanced phenolic acid accumulation, recording 0.14 mg L-1 p-coumaric acid, 0.43 mg L-1 vanillic acid and 1.10 mg L-1 syringic acid, compared with the control. Overall, the application of seaweed extract along with RDF effectively enhanced soil enzymatic activity and microbial colonisation, thereby improving soil biological health and root metabolite functions in wetland acid soils of Kerala.