Soil Carbon Mineralization Kinetics as Influenced by Changes in Land Use and Soil Management in the Central Highlands of Ethiopia

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.

自然植被向其他土地利用及土壤管理系统的转变通常伴随着土壤性质的改变，并具有环境影响。此类土地利用与农业实践的变化会影响土壤碳库，并导致大气CO₂浓度升高。因此，为理解碳矿化过程，研究人员在埃塞俄比亚中央高地采集了五种相邻土地利用及管理系统（草地、农田、桉树人工林、石灰改良地和休耕地）的土壤样本，开展了为期62天的实验室培养实验。与其他土地利用及管理系统相比，草地在0-10 cm和10-20 cm土层的总矿化碳量及矿化速率均持续更高。累积CO₂释放量的排序为：草地>农田>桉树人工林>休耕地>石灰改良地。在测试的六种动力学模型中，一级模型[Ct = Co (1-e⁻ᵏᵗ)]被选中，且能很好地拟合实验数据以描述碳矿化过程。草地的两个土层及农田表层（0-10 cm）的潜在可矿化碳（Co）均值显著高于不同土地利用类型各土层的对应值。石灰改良地和休耕地10-20 cm土层的代谢商（qCO₂）显著高于其他土地利用及管理系统。同样，草地土壤的有机碳（SOC）和微生物生物量碳（MBC）显著高于（p<0.001）相邻的农田、桉树人工林、石灰改良地及休耕地。SOC与MBC与Co、k及Co*k呈正相关，与t₁/₂及qCO₂呈负相关。因此，SOC、MBC、Co及qCO₂是区分不同土地利用及管理系统的更优指标，可作为研究区域生态系统变化的敏感指示因子。