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.