Abstract

                                Improving soil organic carbon by biochar application is of concern in flooded rice soils. However, the effect of biochar on soil physico-chemical and biological properties under increasing levels of CO2 is limited and needs investigation. The present study examined the response of soil carbon pool, and soil enzyme activities of rice upon application of biochar under elevated carbon dioxide (eCO2) - 55030 μmol.mol−1 level. The study was carried out in open-top chambers (OTC) under a rice-rice (Oryza sativa L.) cropping system in 2020. A set of OTCs at ambient CO2 (415 ± 10 μmol mol−1 (aCO2)) served as a check with and without biochar application. The fourth OTC maintained eCO2 without the application of biochar. Rhizosphere soil samples from three critical crop stages viz., active tillering, flowering, and maturity were analyzed for various physico- chemical and biological properties. Most soil biological parameters, specifically soil enzymes, β – glucosidase, urease, and phosphatases, exhibited significant changes during the flowering stage in biochar applied e(CO2) treatment. The per cent increase of 46.8 %, 30.2 %, 18.75 %, and 51.2 % over ambient CO2 in soil organic carbon (SOC), soil microbial biomass carbon (SMBC), oxidizable carbon (OC), and water-soluble carbon, respectively, was observed. This study emphasized that biochar can improve the soil C pool and enzyme activities under anticipated climate change.

Key words : Elevated carbon dioxide; Paddy; C pool; Soil enzymes; Biochar