Review on Impacts of Land Degradation on Agricultural Production in Ethiopia

Land degradation is the result of complex interaction among, physical, chemical, biological, socio-economic and political issues of local, national or global nature. Land degradation affects Ethiopian economy and also has many negative impacts on agricultural productivity by reducing the fertility of agricultural land. Land degradation is increasing in severity and extent in many parts of the world, with more than 20% of all cultivated areas, 30% of forests and 10% of grasslands undergoing degradation. Millions of hectares of land per year are being degraded in all climatic regions. It is estimated that 2.6 billion people are affected by land degradation and desertification in more than a hundred countries, influencing over 33% of the earth ́s land surface. The global store of arable land and grazing land continuous to decline through urbanization, un sustainable agriculture practices and deforestation, while, significant portion of the remaining arable land and grazing land is under considerable pressure from compaction by livestock and farm implements, over use of fertilizers and pesticides, Salinization, alkalization or acidification depletion of nutrients, water and wind erosion, deterioration of drainage. The velocity of land degradation is high due to, Improper tillage operation on the land, Poor managements of land, The attitude of the community about the consequences of land degradation on agricultural productivity, Lack of knowledge of the farmers about the main biological, physical and mechanical methods of land conservation. The agricultural impacts of land degradation are, loss of soil nutrient, Soil erosion effects, reduction of crop yield, silting up of reservoir and It also contributes to persistent poverty, and results in decreasing ecosystem resilience e and provision of environmental services. In addition, environmental decline due to land degradation adversely affects the health, well-being and livelihood opportunities of the individuals.

 Improper tillage operation on the land  Poor managements of land  The attitude of the community about the consequences of land degradation on agricultural productivity  Lack of knowledge of the farmers about the main biological, physical and mechanical methods of land conservation Various types of human activities can be identified as the direct cause of land degradation within the high Pamir and Pamir Alai mountains, the most important are believed to be (Kland,2008).
 Over reliance of fuel wood, shrubs, dung and peat to meet house hold energy needs  Poor pasture management in particular the over grazing of pasture areas close to the village  Poor soil and water management in plots used for irrigation rain fed crop production system  Poor construction and maintenance of irrigation system

Natural cause of land degradation
The natural factors causing land degradation includes high intensity of rain fall, types of soil, topography, earth quack, volcanic eruption and steep relief is the major ones; impact of rain drop with tremendous amount of energy. On bare un protected soil starts the process of erosion by water. Generally, distribution frequency and intensity of rain fall are the major factor affecting land degradation. Gentle rainfall distributed more evenly throughout the year causes less land degradation than heavy rainfall concentrated only to a few months. More frequently rain fall cause more land degradation than that of less intensity. According to the law state university extension web site during normally rain fall millions of rain drop from 1 -7mm in size will pound the surface and splash soil particles 3-5feet way from where they were before the rain and cause land and soil degradation (Narayana ,2004) 2.2.1.1. Erratic rain fall Distribution, frequency, intensity and timing of rain fall energy produced by rain fall are among major factors affecting the land degradation. The severity of the land degradation dependent on those parameters when those factor are with higher degree, then severity of the degradation of land is also higher and the reverse is also true. Gentle rainfall distributed more over through the year cause of less land degradation than heavy rainfall concentrated only few month rain fall evenly distributed over water shed (Bekele, 2003). More frequent rain fall causes more degradation the less frequent one.
Rain of high intensity causes more land degradation than that of less intensity. According to the law state university extension web site during normal rain fall millions of rain drops from one to seven millimeter in size fill pound the surface and splash soil particles three to five millimeter frequency from where they were before the rain and causes land and soil degradation (Naryana and Babu, 2004).

Human Induced Causes of Land Degradation
The manmade land degradation includes production on steep slopes and fragile soils with inadequate investment in soil conservation or vegetation cover, declining use of fallow, limited recycling of dung and crop residues to the soil, limited application of external source of plant nutrient, deforestation and overgrazing. The cause also includes proximate causes such as population pressure, poverty, high costs of and limited access to agricultural inputs and credits, low profitability of agricultural production, farmers" lack of information about alternative technology. Moreover, in order to survive in subsistence economy, farmers are forced to mine soil and to cut down trees leading to land degradation (Hurni, 1999).

Deforestation
Deforestation is the clearing or removal of tree from an area woody land or forest of tree an area woody land or forest for many reasons usually commercially. It is one of the major issues in this century since it is one of the many causes of prevailing land degradation. Tree cutting is common occurrence which has taken place for centuries. Hundreds of year back in history some parts of our country continents which are suffering from conditions caused by land degradation (Esdoman, 2006).
The scale and extent of deforestation in prehistoric and historic times early varied continent to continent and from country to country. The causes of deforestation are in fact man made and most of them derive from the highly increasing number of population which can directly due to the land resources by resulting sever form of soil erosion which leads to land degradation (Buckmans, 2007).

Over population
Population increase has been one of the frequent cause of land degradation. There has been debate on relationship between population number, growth rate and agricultural development, particularly the intensity of farming system. That means as the number of population increase, the required land for agriculture, house hold construction and other activities increase. This lead so miss management of land without knowing their degraded form (Gok, 2002). The population of the world is increasing at an alarming rate. Land redistribution, which in recent year has been the only means of normally acquiring access to land accommodate new households has lead to sever fragmentation of plots, reduction of crop yields and in security. Reduction of crop land per capital and in security have lead to the reduction in activities such as, fallowing, planting trees and investing in conservation structures. While a reduction in crop land per capital has caused cropping and grazing activities to be shifted to hill side and ecological damaged areas (Bhargava, 2005).
The Ethiopian population increasing day to day and resulted in rapid deforestation, sever soil erosion and alarming environmental degradation (Tamene et al., 2006;Nyssen et al., 2009). Soil erosion creates severe limitation to sustainable agricultural land use, as it reduces on farm soil productivity and food security (Mogos and Holden, 2006;Bewket, 2007).
General negative impacts of overpopulation for rapid land degradation includes (Bolan, 2008)  It results in rapid expansion of different form of erosion  It facilitates over use of land resources  As population number increases the demand of people to obtain land for agricultural purpose can be highly increase. As result, deforestation takes place and it affects land.
 As population number increase rapidly, then activities of humans to satisfy their different needs becomes highly increase, as a result deforestation takes place and it affect land.

Traditional farming system
It refers to a type of farming practice that farmers are following without properly identifying the relationship between crop soils requirement and without following several soil and water conservation measures which are highly vital for conservation of land resource and compromising of future generation benefits (Moltimore, 2005). The productive layer of dirt is called top soil. If this eroded away through back ward farming system, then land is very unproductive in producing crops soil can be eroded away by wind and Water. High winds can blow away loose soil from flatter, hilly terrain, Water erosion generally occurs on slopes and its severity increase with the severity of slope (Voteberg, 2009).

Soico-Economic and Institutional Factors
Socioeconomic and institutional factors are the underlying causes that affect land degradation through their impacts on farmers" decisions with respect to land use and land management practices. For example, absence of a comprehensive land use and administration policy, proclamations, laws, regulations and master land use plans developed in a participatory at federal, regional, and community level are the major factors that have contribute to the unchecked land degradation in the country (Gebre eyesus, 2009).

Major Impacts of Land Degradation on Agricultural Productivity
Land degradation manifests itself in many different ways: vegetation becomes increasingly scarce, water courses dry up, thorny weeds predominate in once rich pastures, footpaths grow into gullies, and soils become thin and stony. All of these manifestations have potentially severe impacts on the environment, for land users and for people who rely for their living on the products from a healthy landscape (Berry, 2003) 2.5.1. Agricultural impacts of land degradation 2.5.1.1. Soil erosion effects Soil erosion is the processes in which soil and rock are removed from the earth surfers by exegetic process such as wind or water flow ,ways of numerous physical, chemically and biologically process which include weathering with associated erosion .soil erosion from land area is wide spread and already adversely affected all natural and human managed ecosystem including agriculture and forest for that reason soil erosion ranks as one of the most serious environmental problem in the world, which is the effect of land degradation .It effects are pervasive and its damage are long tasting (Pimentel, 2005).
Although soil erosion has occurred throughout history, it has intensified expanding human population coupled with their diverse activities, intrude further in to natural ecosystem, thereby reducing the productivity of the land as result the diversity of the plant, animals, and microbes redimmished ultimately the stability of entire ecosystem threatened (Pimentel et.al., 2005).

On -site effects
The breakdown of aggregates and the removal of smaller particles or entire layers of soil organic matter can weaken the structure and even changes the texture, textural changes can in turn affect the water -holding capacity of the soil, making it more susceptible to extreme condition such a drought (Berry, 2003).

Off-site effects
Off-site impacts of soil erosion are not always as apparent as the on-site effects. Eroded soil, deposited down slope can in habit or delay the emerges of seeds, bury small seedling and necessitate replanting in the affecters area.
Pesticides and fertilizer, frequently transported a long with the eroding soil can contaminate or pollute downstream water sources and recreational areas (Morgan, 2000). Water erosion main off-site effect is movement of sediment and agricultural pollutants in to water course. This can leads to the silting up of drinking water .In some cases, increase downstream flooding may also occur due to the reduced capacity of eroded soil to absorb water. Movement of sediment and associated agricultural pollutants in to water course is the major off-site impact resulting from erosion (Dave, 2005).

Loss of nutrients
When soil is eroded basic plant nutrients such as; nitrogen, phosphorus, potassium and calcium also lost eroded soil typically contains about the three times more nutrient than the soil left behind on the eroded land (Lat, 2001).Aton of fertile soil typically contains one up to six kilogram of nitrogen, 1-3kg of phosphorus and 2-30kg of potassium whereas the soil on eroded land frequently has nitrogen levels of only 0.1-o.5kg/t (Alexander, 2001 andTorch 2002).Once the organic matter layer is depleted the productivity the ecosystem as measured by crop .Plant yield declines both because of the degraded soil structure and depletion of nutrients contained in organic matter (Lat, 2001).

Reduction of Crop Yield
By diminishing soil organic matter and over soil quality soil erosion reduce biomass productivity in ecosystem ultimately this a profound effect on the diversity of plant , animal, microbes and other forms of life present in ecosystem .Plants, animals and microbes as well as other form of life present in the ecosystem are a vital component of the soil as mentioned and constitute a large measure of the soil biomass (Lee E ,2006).Indirect effect of erosion on ecosystem frequently may nearly as damaging as the direct effect of reducing plant productivity. For example; the stability and biodiversity of grass land where significantly reduced when plant species reduction occurred (Tillman, 2004).

Silting up of reservoirs
Silt resulted runoff water often result in the silting of reservoirs that in the path of a river or stream. Water in the reservoirs is where nearly still, and therefore, a great proportion of the soil brought by the streams dropped out. A good deal of the silt, clay and organic matter remaining in the suspension are carried to the lower end of reservoir. The rate at which reservoirs are filled up with the sediment depends on the erodability of the soil in the contributing water shed, its topography, climate, type of agriculture and the ratio between the size of the water shed and the volume of the reservoirs (Gray, 2002). Generally, the silting up of reservoir can have great direct or indirect impact on the agricultural productivity on an area.

Socio-Economic Impact of Land Degradation
Land and water degradation threaten food security for many of the poorest and most food insecure living in Asia, Africa and Latin America. It also contributes to persistent poverty, and results in decreasing ecosystem resilience e and provision of environmental services ( Bossio et al. 2004). In addition, environmental decline due to land degradation adversely affects the health, well-being and livelihood opportunities of the individuals (Vivian et al., 1994;Scherr and Yadav, 1996;Fit sum et al., 1999). Due to the presence of land degradation, Africa as a whole has become a net food importer since the mid-1980s. However, the economic implications land degradation is particularly severe in Sub-Saharan Africa because 65% of the population is rural and the main livelihood of about 90% of the population is agriculture (PDF, 2007). The most serious problem of Ethiopia"s land resources is soil erosion. Every year the country is losing billions of birr in the form of soil, nutrient, water and agro biodiversity losses (Paulos, 2001).
As a result, poverty and food insecurity are concentrated in rural areas (MoARD, 2010). Estimates vary considerably but direct losses of productivity from land degradation in Ethiopia are minimally 3 percent of agriculture GDP (Berry, 2003).
Land degradation is one of the major causes of low and in many places declining agricultural productivity and continuing food insecurity and rural poverty in Ethiopia (IFPRI, 2005). The Ethiopian highlands are affected by deforestation and degraded soils, which have eroded the resource base and aggravated the repeated food shortages caused by drought (Tilahun et al., 2001) Land degradation reduced livestock productivity as a result of reduced grazing resources, loss of nutritious plants and grass species (Fit sum et al.1999). Due to land degradation, increased runoff and reduced infiltration contributes to flooding problem (Destaet al.2000;Bezuayehuet al., 2002). Deforestation and desertification adversely affect agricultural productivity, the health of humans as well as of livestock, and economic activities such as ecotourism (UNCCD, 2004).
Similarly, Shibru (2010) reported that the loss of soil productivity in Limo Woreda leads to reduced farm income and food insecurity, particularly among the rural poor and thus continuing or worsening poverty. Land degradation can contribute directly to poverty by reducing the availability of other valuable goods and services important to poor households (for example, fuel wood, construction materials, wild foods, and medicinal plants) and by increasing the demands on labor needed to forage for such goods.

CONCLUSION
Land degradation affects Ethiopian economy and also has many negative impacts on agricultural productivity by reducing the fertility of agricultural land. Being a common problem in Ethiopia, land degradation puts disastrous impact on the socio-cultural environment, ecological setting of the country and also many agricultural impacts. Some of those, soil erosion, loss of nutrients, reduction of crop yield and setting up of reservoirs. The major causes include rapid population increase, severe soil loss, deforestation, low vegetative cover and unbalanced crop and livestock production. In addition, topography, soil types and agro-ecological parameters are contributing factors in the degradation processes influenced by man. To control and degradation, conservation measures throughout history are mainly focused on physical conservation structures which have less contribution for the addition of nutrients removed and to control soil erosion as compared to vegetation measures.