Soil organic carbon and total nitrogen stocks as affected by topographic aspect and vegetation in the Bale Mountains, Ethiopia

Soil organic carbon (SOC) and total nitrogen (total N) stocks in 0–0.3 and 0.3–1.0 m soil layers were estimated following the standard procedures for three vegetation communities; Schefflera-Hagenia, Hypericum-Erica-Schefflera, and Erica arborea (shrub size), at different topographic aspects (east-, west-, north- and south-facing) on the Bale Mountains in the south-eastern highlands of Ethiopia. The results showed that SOC and total N in the top 0.3 m depth varied significantly among vegetation communities (p < 0.001) and aspects (p = 0.003). At all aspects studied, the overall mean SOC and total N amounts to a depth of 1.0 m ranged from 32.67 to 46.03 kg C m− 2 and 2.89 to 3.61 kg N m− 2 among the vegetation communities. The overall mean SOC and total N stocks to a depth of 1.0 m varied from 35.13 to 44.97 kg C m− 2 and 2.90 to 3.75 kg N m− 2 among aspects. Topographic aspect induced microclimatic differences and vegetation community types were found to be important factors for the significant variations in SOC and total N stocks in the Bale Mountains. About 45% of the SOC stock in the 0–1.0 m layer of the mineral soil was held in the top 0.3 m of the soil, indicating the potentially large amount of CO2 that can be released from the top surface soils when these vegetations are deforested and converted into grazing and cultivation.