Impact of carbonates on the mineralisation of surface soil organic carbon in response to shift in tillage practice.

Abstract The inorganic soil C pool is a major source of CO 2 emission into the atmosphere along with the soil respiratory CO 2 fluxes but is comparatively less studied than the organic C mineralisation processes. This study aims to understand how soil available carbonates influence the soil C dynamics under different tillage, mulching and temperature regimes. A 90-day incubation experiment was conducted by adding calcite nodules to soils (10% w/w) collected from an agricultural field maintained with or without 5 t ha−1 mulching under no-till (NT) or conventional tillage (CT) systems. Environmental Scanning Electron Microscope (ESEM) examination indicated greater morphological changes in the calcite nodules incubated with CT than NT soils. Soil samples incubated with calcite and mulching recorded 6.3% greater CO 2 evolution than the un-mulched condition. Under the CT system, the overall CO 2 emission rate was higher in the control treatment (43%), followed by a combined treatment of 5 t ha−1 mulch + CaCO 3 (10% w/w) (29.2%), 5 t ha−1 mulch only treatment (27.9%), and 10% CaCO 3 (w/w) (16.5%) treatment, with a rise in incubation temperature from 22 °C to 37 °C. Kinetic model calculations for CO 2 emission indicated a greater half-life of easily mineralisable C pools in the NT system at 22 °C. Microbial biomass carbon (MBC) results further verified that the high temperature and disturbed soil conditions limit the availability of soil MBC under the CT systems, indicating a higher decomposition rate. Eventually, these results indicated that agricultural management practices, including tillage shift, explicitly influence the different functional components of soil organic matter (SOM). Highlights • Overall C mineralisation was higher under CT (20.1%) than NT (9.9%) system. • Tillage shift reduced the hydrophobic SOM components by 19.3% than NT system. • The half-life of soil labile C was 6–12 and 5–7 days at 22 and 37 °C, respectively. • Carbonate C started mineralising after interaction with crop residue mulch. [ABSTRACT FROM AUTHOR]