Soil Carbon Stock in Non-traditional Black Soils of North Eastern India: Tripura as Example

Tripura state in the north-eastern region (NER) of India, by its geographic location and richness in biodiversity, well supported by complementary climatic factors, more particularly high rainfall for luxuriant phyto-biomass (both above and below ground) in the form of forests and allied sources of vegetation, are known as non-traditional black soil area. Studies conducted on the soils of Tripura indicate that about 18.20 per cent area of the State consists of black soils. The study attempts to identify the important factors responsible for the formation of black soils even in the non-traditional black soil area of the north-eastern region in general and Tripura state in particular. These black soils are deep to very deep and are mostly dominated by smectitic clays. Such soils resembled the Vertisols mapped elsewhere in other parts of the country concerning texture, periodical opening and closing of cracks and subsurface colour but have dissimilarity for slickenside development, wedge-shaped structure and colour on the surface. The CEC of these soils indicate the dominance of low-activity clays (LAC). However, the clay CEC of these soils are more than 30 and it has been extended up to 60, indicating mixed mineralogy and dominance of smectites or hydroxy interlayered smectites in the clay fraction, which holds more nutrient and moisture and thus converts these areas as the granary of the State. Therefore, besides the dominating effect of humid climate with cooler winter months with profuse vegetation, the soil substrate quality (quality and quantity of expanding clay minerals) is of fundamental importance in the sequestration of OC in the soil. The study indicated that within the 0-30 cm soil depth, black soils of Tripura has got the capabilities to store 0.01Pg soil organic carbon stock which is about 20 per cent of the SOC stock of whole Tripura and 0.01 per cent of SOC stock of India. These soils are more fertile, holding more nutrients and moisture and are still in the weathering stage and show the presence of HIS and HIV in their mineralogicalmakeup. Therefore, the present information will be helpful for developing appropriate land use plans and conservation planning to ensure the green belt in northeastern India in general and Tripura state in particular to protect natural ecosystems.