Morpho‑physiological and biochemical response of coriander to silicon with bacterial inoculants in silicon-deficient soil

Silicon (Si) deficiency limits plant growth, physiological efficiency, and yield in high-value crops such as Coriandrum sativum L. A field experiment was conducted on Si-deficient soil at TNAU Coconut Farm, Coimbatore, India, using coriander variety CO (CR) 4. Seven treatments in a randomized block design with three replications evaluated calcium silicate (CaSiO 3 ), and rice husk ash (RHA) at 225, and 275 kg Si ha − 1 , alone, and combined with Bacillus altitudinis SSB4, across growth, physiological, biochemical, antioxidant, and yield parameters. Si + SSB4 integration significantly improved plant height (up to 60.9% over control), leaf area index, SPAD index, and shoot and root dry matter production. Leaf Si content increased by 84.1–88.4% over absolute control, and 21.7–24.5% over RDF alone. Antioxidant enzymes (CAT, POD, and SOD), and biochemical attributes (total soluble sugars, total soluble protein, total phenols, and ascorbic acid) were markedly enhanced, with total soluble protein recording the highest increase (194.8% over absolute control). RHA-based treatments marginally but non-significantly outperformed CaSiO 3 -based treatments. The highest leaf yield (5.46 t ha − 1 ) was recorded with RDF + RHA at 275 kg Si ha − 1 + SSB4 (53.8% over RDF), followed by RDF + CaSiO 3 at the same level (52.1%). Strong positive correlations ( r = 0.863–0.990) among Si content, antioxidant enzymes, biochemical parameters, and yield confirmed a coordinated Si-mediated improvement. Integrated application of CaSiO 3 or RHA with B. altitudinis SSB4 synergistically enhanced growth, antioxidant defence, biochemical quality, and leaf yield of coriander in Si-deficient soils, supporting the adoption of combined chemical-biological Si management strategies.