Quantitative assessment of water soluble fractions of organic carbon in deep soils under rice and non-rice ecology

Abstract

Soil is the largest terrestrial sink of Carbon (C). Carbon sequestration in soil is important for soil quality as well as to mitigate CO2 loading in atmosphere. Study on C of surface soil layer is going on for long time. Only in the recent past, scientists have noticed the importance of subsoil as a store house of stable C. On the contrary, 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 temperature. In this context, this study tried to understand the dynamics of soil C in deep soil under rice and non-rice ecology. Three distinct long term experimental sites were selected for soil sampling from three eastern states of India. Results indicated high total C and total organic C in surface soil in comparison to subsoil. On the other hand, rice soils had higher C than non-rice soil. The soil C was further divided into labile and recalcitrant pools using water extraction. As per water solubility, water soluble (room temperature) and hot water soluble C was highest in surface soil. This is natural as these pools represent labile C and surface soil receives maximum fresh C input in terms of deposited leaf and litter. The remaining C, not dissolved in water, was considered as recalcitrant C. While considering the water soluble pools as well as recalcitrant C as % of total organic C, trend indicated more labile C (water soluble) in surface soil while subsoil has more recalcitrant C. Therefore, 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.