Influence of Clay Mineralogy on Soil Organic Carbon Stabilization under Tropical Climate, India

Mechanisms of soil organic carbon (SOC) stabilization has received much focus recently due to its relevance in controlling the global carbon (C) cycle. Clay minerals are known to stabilize SOC through mechanisms such as, ligand exchange, polyvalent cation bridging, electrostatic attraction, H-bonding, and van der Waals forces. Most studies focused on clay organic interactions derived from geological deposits. However, the effect of pedogenic clay on SOC stability is still lacking especially in tropical conditions like India. Therefore, the impact of clay with different mineralogy such as smectite, 2:1 interstratified minerals, illite, kaolinite on soil C mineralization, and labile C fractions in four distinct soils under natural conditions was evaluated. The results indicated that the cumulative C mineralization (CO 2 -C cum ) was the highest in Mollisol (0.97 g C kg -1 ) and Vertisol (0.96g C kg -1 ), which was dominated by kaolinite+illite+chlorite–interstratified minerals and smectite/2:1 interstratified minerals, respectively followed by Alfisol and Inceptisol, which was dominated by kaolinite and illite. The percentage of SOC loss showed opposite trend where the highest SOC loss was accounted in Inceptisol (10.1%) and Alfisol (9.02%) whereas Mollisol and Vertisol lost lowest amount of SOC. Labile C fractions and dehydrogenase activity were significantly higher in Mollisol and Vertisol over Alfisol and Inceptisol. Specific surface area (SSA) ( r = 0.65, P ≤ 0.05) and cation exchange capacity (CEC) ( r = 0.62, P ≤ 0.05) positively correlated with C mineralization and labile C fractions and negatively correlated with percentage SOC loss. Principal component analysis confirmed that varying mineralogy significantly influenced the sequestration of labile C in soil under natural conditions. This study highlighted the positive influence of 2:1 expanding/limited expanding clay mineralogy in sequestering and stabilizing labile C in soil.