Does the accretion of carbon fractions and their stratification vary widely with soil orders? A case-study of an Alfisol and an Entisol of sub-tropical eastern India

Comparison of the carbon (C) stocks among different soil orders allows us to explore the role of various soil characteristics in long-term C storage and their vulnerabilities. This study quantified and compared the accumulation rates of soil organic carbon (SOC) fractions (in 0-60 cm soil profile) in an Alfisol of Malda (25 degrees 27 ' 33.9 '' N, 88 degrees 19 ' 10.2 '' E) and an Entisol of Cooch Behar (26 degrees 09 ' 62.7 '' N, 89 degrees 53 ' 51.7 '' E) districts of West Bengal, India. We noticed a greater level of SOC (0-60 cm depth) in the Alfisol than the Entisol as the former soils were clayey in nature (fine textured) which provided the maximum stabilization of SOC compared to the Entisol (sandy textured). However, the storage of C fractions showed some peculiar results. The concentration of mineral-associated carbon (Min-C) was more or less similar in both the soil orders, but its stock was maximum in the Alfisol. While in the Entisol, permanganate oxidizable carbon (POX-C) and particulate organic matter carbon (POM-C) stocks recorded maximum among all the studied depths. A positive relation of SOC fractions and stocks with clay (r(2) = >0.500 in the Alfisol; r(2) = >0.700 in the Entisol) indicated the importance of finer fractions in profile storage of C. Min-C contributed to SOC of about 75%-85% followed by POM-C (3.27%-17.87%) and POX-C (2.57%-4.22%). Higher stratification of SOC and POX-C and POM-C fractions was observed in Entisol; while in Alfisol, stratification of Min-C was greater. Overall, this research demonstrated that the Alfisol has a greater potential in stabilizing Min-C than the Entisol with POM-C and POX-C and the distribution of these fractions varied as per its stabilization.