Land degradation is a major wide-ranging issue for the 20th century and will remain high on the intercontinental agenda even for the 21st century (Working Group on Land Degradation and Desertification of the International Union of Soil Sciences, 1999). Various sources suggest that 5 to 10 million hectares in the world are being ruined annually. If this trend continues,1.4 to 2.8 % of the total agricultural, pasture, and forestland will be lost by 2020 (Scherr and Yadav, 1996).
Soil degradation is a global threat (Wang et al., 2013). Developing countries are more severely affected by soil degradation than developed countries.
Ethiopia, one of the developing countries in eastern Africa, is highly threatened by soil degradation problems (Hurni et al., 2007). Soil deterioration is a serious problem in Ethiopia, particularly in the high lands, where population density is high and the bulk of crop production occurs (Hurni et al., 2007). The pressure from human and livestock populations, coupled with biophysical, social, economic, and political factors, has caused severe degradation of resources (Girmay et al.
, 2008). Depletion of soil organic matter (SOM) and nutrients, salinization, and soil erosion by water is the most critical forms of soil degradation (Girmay et al. 2008) and are aggravated by deforestation. Soil erosion by water is by far the most prominent process of soil degradation in the highlands (Haregeweyn N., 2013). It causes an annual loss of 30, 000 ha (0•03%) of land area (EC-FAO, 1998; National Review Report, 2002) and 1•5 billion megagrams of soil and severely damages over two million hectares (Hurni, 1993). An average soil loss is about 42 Mgt ha-1 yr-1on croplands and can be as much as 300 Mgt ha-1 yr-1 on individual fields (Hurni, 1993).
However, there are no recent nationwide studies that show its recent magnitude.
Soil degradation affects the means of support of lots of people in Ethiopia; it reduces soil productivity and hence contributes to food insecurity and economic losses and aggravates the effects of the recurrent droughts (Mitiku H., 2006). The Food and Agriculture Organization (1986) estimated the average annual productivity drop of cropland due to soil erosion at 2•2%. Over the past three decades, per capita, food production in Ethiopia has declined from about 280 to 160 kg yr-1 (Awulachew T. 2010). Mitiku H. et al. (2006) reported that crop yield is declining by 1–3% y-1, but the population is growing at a rate of 3% y-1, leading to a serious food–population imbalance. Ethiopia has often faced a food deficit in the past (Bewket work, 2003) and may also face even more severe shortages in the future. Soil degradation also increases the vulnerability of people to the adverse effects of climate variability and change, by reducing soil organic carbon (SOC) concentration and water.
Land deterioration is a severe environmental problem in sub-Saharan Africa, and Ethiopia is among the most affected countries (Abiy T., 2008). The productive land in Ethiopia generally and the Southern region especially has been bare to degradation and threat to both the economic and survival of the people (Genene and Abby, 2014). Soil erosion is a major part of land degradation that affects the properties of soils and results in on-site nutrient loss and off-site sedimentation of water resources in Ethiopia (Hurni, 1993). In Ethiopian highlands, high population pressure, continuous and steep slope cultivation, low vegetation cover, deforestation, and inadequate soil conservation practices cause annual soil of about 1.5 billion metric tons (Tamrat et al.,2018). The ever-increasing land-use change is aggravating the rates of soil erosion, soil fertility reduction, crop yield decline, and food insecurity (Haregeweyn N., 2005)
To combat land degradation at a nationwide level, environmental conservation and land restoration effort was started in the 1970s, with a particular focus on the construction of physical structures(bunds, terraces, etc.) in the fast deteriorating highland areas of Ethiopia (Abinet T. 2011). These efforts intend to reduce soil erosion, restore soil fertility, rehabilitate lands, improve microclimate, and boost agricultural production and productivity (Woldeamlak B., 2007). Besides the physical structures, implementation of biological soil conservation practices (e.g., vegetative barriers, agronomic, alley cropping, grass strip establishment), and application of farmyard and green manures in degraded lands become immersed practices across the country (MoARD, 2005). Integration of biological practices with physical structures is highly contributed to the improvement of soil fertility.
In degraded watersheds, opportunities for water collecting and administration are few and of limited use; access roads are continuously spoiled by runoff and erosion, and siltation, access to clean water for domestic use is very difficult and the prevalence of water-borne diseases is very high.
Unstable watersheds induce unstable production systems and inefficiency of input utilization, as erosion and inefficient use of rainwater also undermine efforts to enhance productivity. Increased vulnerability to drought and food insecurity is directly linked to the degraded conditions of the watershed and their effect on limiting its capacity to support local livelihoods thereby reducing the adaptive capacity of rural households face to climatic risks. This is mainly due to depletion of essential nutrients by erosion, water stress due to the limited capacity of soil to absorb more runoff, and soil fertility reduction because of human and natural factors.The opposite occurs with protected and well-managed watersheds, which generate multiple positive effects on people’s livelihoods, the environment, and for the overall economy of the area (Lakew Desta et al., 2005)
It has been generally accepted because world climate is changing more dynamically at present than at any period in the past putting greater pressure on the well-being of human beings as well as the earth system. Climate change and development are highly intertwined. They are related to each other. The risks of global warming could threaten decades of development efforts, particularly in the poorest regions of our planet. There is growing evidence that climate change, specifically higher temperatures, altered patterns of precipitation, and increased frequency of extreme events such as drought and floods, is likely to depress crop yields, and livestock production and increase production risks in many world regions (IPCC, 2001). Thus the debate has now shifted from high-level encouragement on “the need to act”, as this argument seems to be essentially over, to regional and country-level responses on “how to adapt” (Schiermeier and Wilby, 2007)
African countries especially sub- Saharan, are likely to be the most affected by climate change because of limited skills and equipment for disaster management, limited financial resources, weak institutional capacity, and heavy dependence on rain-fed agriculture (F.Bagamba et al.,2012). So irrigation practices should be expanded to have more income. Moreover, the majority of the population survives on agriculture, which makes them more vulnerable (F. Bagamba et al., 2012). The problem of climate change and climate variability is compounded by poor soils in most parts of Sub-Saharan Africa (SSA); caused by poor production techniques and lack of appropriate policies about use of inputs (fertilizer) and access to credit, lack of advanced technology,limited information on climate hazards, (F. Bagamba et al,2012)
Climate change is a great challenge in Africa predominantly in the SSA region, including food insecurity (F. Bagamba et al., 2012), widening and deepening poverty, epidemics (e.g. HIV/ AIDS), and increasing crop and animals pests and diseases, and ineffective governance (IPCC, 2001). In the Eastern Africa region, the increase in the gap between population growth and agricultural capacity is aggravating the already declining food security, and increasing vulnerability and rural poverty, which amplify the impacts of droughts that appear to have become more severe in the recent years.