Long-Term Effects of Rice and Non-rice Ecology on Pools of Carbon in Surface and Deep Soil in Farmer’s Field

The greatest terrestrial sink of carbon (C) is soil. In addition to improving soil quality, carbon absorption in soil helps reduce atmospheric CO2 loading. Not only the surface soil, but also the deep sub-soil act as a storehouse of C. Besides, the study of C dynamics in tropical rice soil is important in countries like India where rice is the predominant crop and soil C sequestration is at risk due to high temperatures. In this context, this study tried to understand the C dynamics in surface as well as deep soil under rice and non-rice ecology. Representative soil samples were collected from five sites of rice-rice (rice ecology) and vegetable-vegetable (non-rice ecology) cropping systems from three depths viz., 0-20 cm, 100-120 and 120-140 cm from long-term farmer’s field of Nadia district of West Bengal belonging to Alfisols to compare C dynamics of surface and deep soils as well as rice and non-rice ecology. Results indicated that surface soils exhibited higher amount of total C, total organic C and inorganic C in comparison to deep soil irrespective of crop ecologies. The rice ecology showed higher total C and total organic C in comparison to non-rice soil. As per water solubility, water-soluble (room temperature) C and hot water-soluble C which were highest in surface soil compared to deep soil as the former usually receives maximum amount of fresh C input compared to deep soil. Irrespective of crop ecology, water-soluble C (WSC), hot water-soluble C (HWC), recalcitrant C (RC) were highest in surface soil compared to deep soils. Again, irrespective of soil depth, WSC and RC were highest in rice ecology and lowest in non-rice ecology. But, HWC content was highest in non-rice ecology and lowest in rice ecology. Irrespective of crop ecology, per cent contribution of labile pool of C (WSC+ HWC) and that of RC pool towards TOC was the highest and the lowest respectively. However, irrespective of soil depth, per cent contribution of labile pool of C and that of recalcitrant pool of C towards TOC was highest and lowest in soils under non-rice ecology and rice ecology respectively. Thus, this study conclusively indicated the potential of subsoil layer to act as a C sink in comparison to surface soil. The rice soil also has been identified as a niche for soil C sequestration.