Total and labile pools of soil organic carbon in cultivated and undisturbed soils in northern India

Labile fractions of soil organic matter (SOM) have been used as indicators for land use induced changes in soil quality. Differences in soil C pools under row crop production and uncultivated soils may provide information about soil C sequestration. The impact of agroforestry consisting of poplar with wheat, rice-wheat, maize-wheat and sugarcane agro-ecosystems on total organic carbon (TOC) and labile pools, viz. water-extractable (WEOC), hot water-soluble (HWC), KMnO4-oxidizable, microbial biomass and mineralizable C; and organic C fractions of different oxidizability was studied at 22-sites for each land use. Cultivation resulted in decrease in TOC (21-36%) and dehydrogenase activity (by 2.8-3A mg kg(-1) soil h(-1)) compared to uncultivated soils. Labile C pools, except WEOC, were correlated (P < 0.05), though the amount extracted by different methods varied considerably suggesting that each method enumerated different fractions of TOC. Agroforestry and sugarcane systems were characterized by very labile C compared with uncultivated soils and the soils under rice-wheat and maize-wheat systems. Conversely, uncultivated soils and the soils under maize-wheat and rice-wheat held greater proportion of organic C in recalcitrant fractions. Results suggest that soil organic C (SOC) pools in agro-forestiy and sugarcane systems could be decomposed under land use alterations. However, no single soil C pool alone was suitable as a sensitive indicator for land use induced changes in SOM. A composite of soil indicators encompassing labile C, KMnO4-oxidizable C, non-labile and recalcitrant C, mineralizable C, basal soil respiration, and dehydrogenase activity could distinguish different land use systems. (C) 2014 Elsevier B.V. All rights reserved.