Geo 6

• Soil is a delicate but highly varied composition of mineral particles, organic matter, and living organisms in dynamic equilibrium
• Function of Soils: Medium for plant growth; a habitat for organisms; means of water storage supply and purification
• Mechanical (physical) weathering

  Physical disintegration causes decrease in size without appreciably altering composition. Differential stresses due to heating and cooling or expansion of ice break the rock. Abrasion (erosion by friction) due to water containing sediment or wind carrying debris is another type of physical weathering
• Weathering

  Disintegrates the inorganic substances (rocks) of soils
• Biological weathering

  The process involves the weakening and subsequent disintegration of rock by plants, animals, and microbes. Roots of plants can exert pressure on rocks
• The formation of a particular type of soil depends on parent material, climate, topography, living organisms, and time
• Chemical weathering


  Involves the modification of the chemical and mineralogical composition of the weathered material. Common chemical weathering processes include hydrolysis, oxidation, reduction, hydration, carbonation, and solution
• Soil properties: Physical properties include texture, structure, porosity, etc. that affect air and water movement in the soil. Chemical properties include availability of minerals, electrical conductivity, soil pH, etc. that affect soil biological activity and nutrient dynamics
• FAO has identified 18 soil associations in Ethiopia, with 11 types covering about 87.4% of the land area
• FAO has identified 18 soil associations in Ethiopia in a map of 1:2000000 scale
• Fluvisols


  1. Develop on flat or nearly flat ground, on recent alluvial deposits

  2. Associated with fluvial (river), marine (sea), and lacustrine (lake) deposits

  3. Found at lower regions of rivers like Omo, Awash, Abay, and the plains of Akobo and
• Lithosols, Cambisols, and Regosol


  1. Mostly found in rugged topography and steep slopes

  2. Young, shallow and coarse textured with low water holding capacity

  3. Found in areas of low rainfall

  4. Have limited agricultural use & in most cases, left under the natural plant cover and used for grazing

  5. Found in rugged and steep slopes of Central Highlands, on the Rift Valley Escarpments, and highlands in western Hararghe, Danakil, and eastern Ogaden
• Six major groups of soils based on

  • Environmental condition (parent material, climatic conditions, topography, the way they were formed)
  • Characteristic (significant chemical and physical properties)
  • Agricultural suitability in relation to texture, structure, topography, moisture-storage capacity, etc.
  • Occurrence: general location of the soil types
• Acrisols


  1. One of the most inherently infertile soils of the tropics

  2. Become degraded chemically and organically very quickly when utilized

  3. Have very low resilience to degradation and moderate sensitivity to yield decline

  4. In Ethiopia, they have lost most of the base nutrients and are characterized by low productive capacity

  5. Found along with Nitosols mostly in some pockets of southwestern highlands of Ethiopia where there is high rainfall
• Out of the major soils, 11 types of soil associations cover about 87.4% of the land area in Ethiopia
• Properties affecting soil biological activity and nutrient dynamics

  • Availability of minerals
  • Electrical conductivity
  • Soil pH
• Nitosols


  1. Develop on gently sloping ground mainly from volcanic rocks

  2. Parent materials include trap series volcanic, volcanic ash, and even metamorphic rocks

  3. Associated with highlands with high rainfall and tend to be leached having reddish-brown color

  4. Dominantly found in western highlands (Wellega), southwestern highlands (Kaffa, Illuababora), Southern highlands, Central highlands, and Eastern highlands
• Xerosols, Yermosols, and Solanchaks

  1. Soils of the deserts with low organic content

  2. Extremely subjected to wind erosion and concentration of soluble salts

  3. Poor humus content and nitrogen, but rich in phosphorus and potash and can be very fertile if irrigated

  4. Yermosols are even drier and more problematic than Xerosols

  5. Solanchaks are saline soils which develop in areas of high evaporation and capillary action

  6. Badly managed irrigation schemes may turn soils into solonchaks

  7. In Ethiopia, Xerosols are found in Ogaden and northeastern escarpments, whereas Yermosols and Solonchaks cover the Ogaden and Afar plains

  8. The Solonchaks are majorly located in salty plains of Afar
• Vertisols

  1. Heavy clay highland soils

  2. Swell when wet, and crack when dry

  3. Difficult to manage, but have high natural fertility

  4. Mostly develop on volcanic plateau basalt, trachyte and pyroclastic materials, sedimentary rocks, colluvial slopes and alluvial plains

  5. Commonly found in parts of Northwestern, Central and Southeastern highlands (Gojjam, Shewa, Arsi, Bale and central Hararghe)
• Soil types in Ogaden and Afar plains

  • Solonchaks
• Types of soil degradation include Physical Degradation, Biological Degradation, and Chemical Degradation
• Soil Degradation refers to a change in any or all of soil status resulting in a diminished capacity of the ecosystem to provide goods and services
• Causes of soil degradation include natural and human-induced factors such as topographic and climatic factors, deforestation, overgrazing, indiscriminate use of agrochemicals, and lack of soil conservation practices
• Fluvisols


  1. Develop on flat or nearly flat ground, on recent alluvial deposits

  2. Associated with fluvial (river), marine (sea), and lacustrine (lake) deposits

  3. Found at lower regions of rivers like Omo, Awash, Abay and the plains of Akobo and Baro Rivers

  4. Prized for intensive agriculture because they develop on flat ground, deposition sites, are associated with rivers and ground water, making them important for large-scale irrigation, and are fertile with fertility renewed due to deposition of new soil materials
• Soil degradation is a major concern as it undermines the productive capacity of an ecosystem and affects global climate through alterations in water and energy balances and disruptions in cycles of carbon, nitrogen, sulfur, and other elements
• Soil types in Ogaden and northeastern escarpments


  • Yermosols
  • Solonchaks
• Luvisols


  1. Develop mainly in areas where pronounced wet and dry seasons occur in alteration

  2. Found in association with nitosols

  3. Have good chemical nutrients and are among the best agricultural soils in the tropics, intensively cultivated

  4. Found on steep slopes (Stony) and on flat areas (waterlogged), avoided and left for grazing

  5. Found in places like Lake Tana area, parts of Northern, Central and Eastern Highlands, and Southern lowlands in Ethiopia
• Solonchaks are majorly located in salty plains of Afar
• Soil erosion is a natural process that can be reduced through erosion control measures like biological control measures (vegetative strips, plantation, reforestation) and physical control measures (terracing, trenches)
• In Ethiopia, an estimated average of 42 tons per hectare of soils is eroded annually
• Natural vegetation refers to a plant cover that develops with little or no human interference
• Uses of natural vegetation


  • Shelter, food, source of fuel, pasture and grazing, raw material for industries, source of timber and non-timber products, moderating effect on local climate, home of wildlife, medicinal values, minimizing soil erosion
• The characteristics of Ethiopia's natural vegetation are largely determined by


  Elevation (and temperature) and rainfall
• Physical control measures


  terracing, trenches, contour ploughing, soil bunds
• Ethiopia has the largest extent of Afro-alpine and sub-afro alpine habitats in Africa
• Biological Control measures

  Reduce the velocity of surface runoff, increase infiltration and reduce runoff
• Biological Control measures

  • Vegetative strips, plantation, reforestation
• Physical control measures

  • Wind breaks or shelter belts, check dams
• In Ethiopia, there are approximately 6000 species of higher plants, of which 10% are endemic
• n is a natural process, it cannot be prevented but can be reduced