Soil carbon and nitrogen losses following deforestation in Ethiopia

Abstract

Ethiopia faces high risk of soil carbon depletion for nearly half of its total land mass largely due to forest clearing and continuous cultivation. Conversion of natural ecosystems to cultivated agriculture resulted in losses of between 20 and 50% of the soil C stocks in the first meter of the soil depth. Dry Afromontane forests of northern Ethiopia have faced vast exploitation, and almost all these forests have been converted to agricultural lands affecting the functionality and stability of agroecosystem. Here, we studied the effect of land use-land cover changes on soil organic C, total N, and soil C sequestration. Specifically, (a) we characterized major soils of the Desa’a Dry Afromontane forest, northern Ethiopia, and (b) we analyzed the organic C and total N contents of soils with varying land use-land cover types of the Desa’a Dry Afromontane forest. Results show that soil organic C (1.9%) and total N (0.3%) were higher for the middle landscape position than that observed for the upper and lower landscape positions. Soil organic C that ranged from 1.2 in farmland to 2.3% in dense forest also varied with land use-land cover types. Concentration of soil organic C was different among dense forest (2.3%), open forest (1.7%), grazing land (1.6%), and farmland (1.2%). Due to the effect of land use-land cover types, soil total N varied from 0.2% in the farmland to 0.3% in the dense forest. The soil organic C and total nitrogen of the top and lower layer soils were 2.0 and 1.5 and 0.2 and 0.3%, respectively. The soil organic C sequestration for dense forest was significantly higher (48.5 t ha−1) than that of grassland, open forest, and farm land. The top soil sequestered higher soil organic C (44.9 t ha−1) than the lower soil layer. Thus, the top soil layers of dense forest at the middle landscape positions stored significant amount of soil organic carbon.