Optimizing Vermicompost and Cobalt Application for Enhancing Rice (Oryza sativa L.) Yield in Inceptisol

Purpose: Rice is an essential diet for more than half of the world’s inhabitants and subjected to growth in heavy metal-contaminated soil. Rice accumulates heavy metals in the above and below ground parts; the magnitude of accumulation depends upon the plant's available form of heavy metals in the soil. One such heavy metal is cobalt, which its concentration has been manifolded in post-industrial activities, leading to a high soil Co concentration. Cobalt is a component of Vitamin B12 and many enzymes. Humans can’t synthesize these enzymes, and consumption of Co-enriched grain can lead to Co toxicity in humans. The present experiment aimed to evaluate the effect of vermicompost conjugated with an optimum dose of Co for rice plants grown in an Inceptisol. Method: The experiment was conducted using a completely randomized design (CRD) comprising nine treatments. The treatment received vermicompost, Co in the form of cobalt chloride, and the recommended dose of fertilizer (RDF). Results: The results indicated that the application of Co at lower concentration was beneficial for rice growth without any hyperaccumulation, resulting in a significant increase of 46% and 22% in grain and straw yield, respectively. A comparable trend was also observed for Nitrogen uptake, which increased by 2 and 1.5 times over RDF in grain and straw, respectively. In contrast, higher Co application rates, either alone or in combination with vermicompost, resulted in a 10–15% reduction in cobalt uptake in grains. These findings suggest that vermicompost plays a critical role in regulating and optimizing cobalt uptake under higher Co application levels. Conclusion: Overall, vermicompost and the lower doses of Co provide a better yield in rice without any phytotoxicity. Highlights: · Vermicompost and low-dose Co boosted rice yield by up to 46% over recommended dose of fertilizer · Improved N, Fe, Mn and Zn uptake without Co hyperaccumulation in grain. · Vermicompost raised soil OC and reduced Co uptake, enhancing food safety. · Higher Co (>10 mg kg⁻¹) induced phytotoxicity, lowering growth and yield. · Integrated vermicompost and Co management supports soil and crop health.