Potentially mineralizable carbon in soils under defferent land management

Abstract

Soil organic matter pools provide insight into the potential stabilization or degradation of the soil resource by various long-term land management systems. Potentially mineralizable carbon (PMC) in soil is a measure of easily decomposable carbon and considered an important pool of soil organic matter. PMC was measured in soil samples taken from six different land management types viz. grass, legume, cinnamon, coconut, vegetable and a planted forest located in the low country wet zone of Sri Lanka. Soil samples taken from the different fields were incubated and carbon mineralization during 0-3, 3-10 and 10-24 day periods were determined as total CO2 evolved using alkali (NaOH) traps. Land management significantly influenced the total carbon mineralized during the incubation. Soils from the grass and coconut fields recorded the significantly high PMC compared to other land management types. The PMC in soils ranged from 298 to 428 mg/kg of soil in different land management treat ments. PMC was also calculated based on the carbon mineralized as a fraction of total organic carbon (TOC) in soil. Planted forest had the lowest PMC as a fraction of TOC (1.6%) compared to the highest recorded in the coconut field (5.2%). Results of this study suggest that PMC is related to the vegetation type and the nature of plant litter that supply organic matter to soil. It also appeared that labile carbon is more prevalent under grass vegetation compared to other land management types. PMC in soil could be used as an indicator to assess the amount of labile and easily decomposable carbon in soil.