Biogeochemical appraisal of carbon fractions and carbon stock in riparian soils of the Ganga River basin

Abstract

The farmers are approaching river/reservoir beds to produce crops and vegetables during the lean periods, especially post-monsoon, winter, and summer, for their livelihood in changing climatic scenarios. Comparing C fractions, C stocks, and microbial indices between the terrestrial (conventional agricultural land: CAL) and riparian zones (reservoir riparian zones: RSRZ and river riparian zones: RRZ) reveals that cultivating riparian zones is environmentally stressful and climatically vulnerable to livelihood practices. The moist riverbed conditions for cultivation result in the accumulation of residual biomass and the burial of soil organic matter. The C fractions showed decreasing trends as CAL > RSRZ > RRZ. The mean TOC stock was found high in the CAL soils (45.04 Mg C ha−1) than in the RRZ (40.65 Mg C ha−1) and RSRZ soils (38.01 Mg C ha−1). The labile C fraction (KMnO4-C) varied from 2.34 to 3.29 % of TOC, and the RSRZ and RRZ soils showed 14.50 % and 40.32 % less KMnO4-C than the CAL soils. The relationship between KMnO4-C and mineralizable C (Cmin) showed high potential for organic carbon stabilization in riparian soils. The microbial biomass carbon (MBC) and basal soil respiration (BSR) values were nearly half of the CAL in the RRZ soils indicating limited carbon substrate availability to the microbial decomposition. Low mineralization quotient (qM) and high metabolic quotient (qCO2) indicated stressful microbial utilization of labile TOC in the RRZ soils. The high carbon management index (CMI) showed the potential to store and sequester TOC in riparian soils. The artificial neural networks (ANN) were used to examine the impact of soil properties on the prediction efficiency of TOC stocks in the three farming zones.