Sub-soil organic carbon sequestration and USDA Soil Taxonomy of coastal acid sulphate soils; constraints and their solution learned from a pedon study in the Kole land ecosystem of Kerala, India

Abstract

ABSTRACT A study was undertaken to characterize and classify the soils and to assess the organic carbon stocks in an acid sulfate wetland ecosystem (Kole lands) of Kerala. The excavated profile in the Kole land was studied for morphological, physical and chemical properties. Extreme acidity and sub-surface accumulation of salt enriched organic materials were the key characteristics of the horizons in the Kole land profile studied. The soil was very deep (>150 cm deep) due to the fluvial accumulation of sediments. Loamy sand surface texture and silty clay loam to silty clay sub-surface texture was observed in the pedon. Cation exchange capacity increased in consonance with the increase in organic materials in the deeper layers of Kole land pedon. Kole land soils were classified under the order Histosols due to the very high organic matter accumulation in deeper layers. Based on the results of the study, soils of Kole lands were classified as loamy, mixed, euic, isohyperthermic, Terric Sulfihemists at the family level. The study revealed the inherent limitation associated with USDA Soil Taxonomy in classifying the organic material enriched coastal acid sulfate soils of tropical regions under Histosols order and necessary modification is suggested. On estimating the organic carbon stocks in the soil profile, it was found that maximum soil organic carbon (SOC) was stored in the 90–120 cm soil horizon (1016.56 Mg ha−1) and entire Kole land area can sequester around 229.63 Tg organic carbon in its 150 cm top soil layer.