Magnitude, spatiotemporal patterns, and controls for soil organic carbon stocks in India during 1901-2010

To the best of our knowledge, no attempts have been made to understand how environmental changes that occurred in the 20th century have altered soil organic carbon (SOC) dynamics in India. In this study, we applied a process-based Dynamic Land Ecosystem Model (DLEM), to estimate the magnitude as well as to quantify the effects of climate change and variability, land cover and land-use change (LCLUC), carbon dioxide (CO₂) concentration, atmospheric nitrogen deposition (NDEP), and tropospheric ozone (O₃) pollution on SOC stocks in India during 1901-2010. The DLEM simulations have shown that SOC stocks ranged from 20.5 to 23.4 Pg C (1 Pg = 10¹⁵ g), majority of which is stored in the forested areas in the north-east, north, and few scattered regions in the southern India. During the study period, soils have sequestered SOC by 2.9 Pg C. Elevated CO₂ concentration has increased total SOC stocks over the country by 1.28 Pg C, which was partially offset by climate change (0.78 Pg C) and tropospheric O₃ pollution (0.20 Pg C) during 1901-2010. Interestingly, LCLUC increased SOC stocks by 1.7 Pg C thereby suggesting that SOC loss from deforestation was offset by the conversion of low productive fallow lands and other lands to croplands that received irrigation along with N fertilizers. Atmospheric nitrogen deposition (NDEP) has increased biomass production and SOC by 0.5 PgC over the country. This study has demonstrated that the benefits from elevated CO₂ concentration, cropland management practices, and NDEP in sequestering SOC stocks were offset by climate change and tropospheric O₃ pollution which should be curbed in India.