Conversions of natural vegetation to other land use and soil management systems are often accompanied by changes in soil properties and have environmental implications. Such changes in land use and agricultural practices affect soil carbon pools and contribute to increased atmospheric CO2 concentrations. Hence, to understand carbon mineralization processes, a 62-day laboratory incubation experiment was carried out using soil samples collected from five adjacent land uses and management systems (grassland, cropland, Eucalyptus plantations, limed land, and fallow land) in the central highlands of Ethiopia. Total carbon mineralized and the mineralization rates were consistently higher in grasslands in both 0-10 cm and 10-20 cm as compared to the other land uses and management systems. The cumulative CO2 release followed the order: grassland> cropland> Eucalyptus> fallow land> limed land. Among six kinetic models tested, a first-order model [Ct = Co (1-e-kt)] was selected and fitted well to describe C mineralization of the experimental data. Grassland in both depths and cropland in the surface layer (0- 10 cm) had significantly higher mean values of potentially mineralizable carbon (Co) as compared to each depth in different land uses. Metabolic quotient (qCO2) observed in limed land and fallow land in 10 -20 cm depth was significantly higher than the other land uses and management systems. Similarly, soils under grassland had significantly (p<0.001) higher soil organic carbon (SOC) and microbial biomass carbon (MBC) than the adjacent cropland, Eucalyptus plantations, limed land and fallow land. SOC and MBC were positively correlated with Co, k and Co*k, and negatively correlated with t1/2 and qCO2. Hence, SOC, MBC, Co and qCO2 were better discriminators among different land uses and management systems, and therefore, could be used as sensitive indicators of ecosystem change in the study area.
