Soil Carbon Stock and Pools in Acid Sulphate Soils of Kerala

A study was conducted to assess the soil carbon storage as different soil carbon pools in acid sulphate soils of Kuttanad, Kerala under different land uses and mapping of carbon stock using GIS. Surface soil samples (0-15 cm) were collected from three agricultural land use systems namely rice, coconut and rice-fish from six acid sulphate soil series viz. Ambalapuzha, Purakkad, Thakazhi, Thuravur, Thottapalli and Kallara and were analysed for soil carbon pools like organic carbon, labile carbon, water soluble carbon, particulate organic carbon, microbial biomass carbon and mineralizable carbon using standard procedures .The carbon stock in soil was also computed and mapped using Arc GIS software. The highest organic carbon content of 9.38% was recorded in Kallara series under rice land use. The water soluble carbon ranged from 44.38 to 208.68 mg kg-1. Labile carbon in soil varied form 4.36 mg g-1 to 13.06 mg g-1. Particulate organic carbon was the highest in rice land use in Kallara series (7.23%). The mineralizable carbon ranged from 2.17 mg kg-1 to 2.91 mg g-1. The microbial biomass carbon varied between 71 mg kg-1 and 488 mg kg-1. The humic acid content varied from 0.20% to 6.09% and the fulvic acid content ranged from 0.09% to 20.10%. The active and passive carbon pools and their contribution to total soil carbon pool was the highest in Kallara series. Among the different land uses, coconut had the highest active pool, while rice land use recorded the highest passive pool of carbon. The soil organic carbon stock (115.96 Mg ha-1) and carbon pool index (2.10) were the highest in Kallara series. The proportion of POC to SOC was the highest in Kallara series (0.62) under rice land use indicating it as a potential carbon sink. The carbon turnover rate was found to be the highest in Thottapalli series (1.15) under coconut land use indicating it as a potential carbon source.