3. Land Degradation and Soil Carbon Pool in Different Land Uses and Their Implication for Food Security in Southern Ethiopia

This paper provides an overview of land degradation and a summary of carbon and nitrogen pooling under different land uses in Southern Ethiopia. The conversion of pristine vegetation to cultivated lands depletes soil organic matter (SOM). In this paper, we: (i) explore the extent of the land degradation in Ethiopia; (ii) assess changes in the stocks of soil organic carbon (SOC) and nitrogen (N) in soils under the chronosequences of 12–50 years of traditional agroforestry (AF) and crop fields (F); (iii) discover the effect of plantations on the state of SOC and N; (iv) consider the litter production and in situ decomposition rate under plantations; and (v) evaluate the effect of plantations on soil quality in Gambo District. The rates of soil erosion in Ethiopia hover around 16–300 Mg ha⁻¹ year⁻¹. The SOM loss was estimated to be 1.17–78 Tg year⁻¹ from 78 M ha of cultivated and grazing lands. The SOC stock under the chronosequence of 12–50 years of AF and F land uses varied from 28.2 to 98.9 Mg ha⁻¹, or 12–43 % of the stock, under the NF. The plantations accrued from 133.62 to 213.73 Mg ha⁻¹, or 59.1–94.5 % SOC of that under the NF. Litter fall was higher under broad-leaved compared with the coniferous plantations. The soil quality index was high for NF and Juniperous procera. Plantations may represent the best option for mitigation of the increasing atmospheric CO₂ and sustenance of land productivity. Nevertheless, NF should be protected from further conversion to other land uses to maintain healthy ecosystem functions.