Soil in Atsbi Wenberta


The soils of the Atsbi Wenberta woreda in Tigray reflect its longstanding agricultural history, highly seasonal rainfall regime and relatively low temperatures. The northern part of the district is on the high uplifted Atsbi Horst, whereas the southern part is dominated by the Des'a forest on Antalo Limestone. In between there is the fluvial landscape of Hayqi Meshal. Particularities in the southern part of the district are soil catenas on intervening plains behind tufa dams and in a polje.

Factors contributing to soil diversity

Climate

Annual rainfall depth is very variable with an average of around 800 mm. Most rains fall during the main rainy season, which typically extends from June to September.
Mean temperature in woreda town Atsbi is 17 °C, oscillating between average daily minimum of 9.4 °C and maximum of 24.3 °C. The contrasts between day and night air temperatures are much larger than seasonal contrasts.

Geology

The following geological formations are present in the southern part:
On the northern Atsbi Horst:

Topography

As part of the Ethiopian Highlands the land has undergone a rapid tectonic uplift, leading the occurrence of plateaus, valleys and gorges.

Land use

Generally speaking the level lands and intermediate slopes are occupied by cropland, while there is rangeland and shrubs on the steeper slopes. Remnant forests occur around Orthodox Christian churches, in a few inaccessible places and especially in the Des'a forest. A recent trend is the widespread planting of eucalyptus trees.

Environmental changes

Soil degradation in this district became important when humans started deforestation almost 5000 years ago. Depending on land use history, locations have been exposed in varying degrees to such land degradation.

Geomorphic regions and soil units

Given the complex geology and topography of the district, it has been organised into land systems - areas with specific and unique geomorphic and geological characteristics, characterised by a particular soil distribution along the soil catena. Soil types are classified in line with World Reference Base for Soil Resources and reference made to main characteristics that can be observed in the field.

[Enticho Sandstone] plateau

  • Dominant soil type: shallow, very stony, silt loamy to loamy soils
  • Associated soil type: complex of rock outcrops, very stony and very shallow soils
  • Inclusions
  • * Shallow, dark loamy soils with a good natural fertility
  • * shallow, stony loam soils

[Mesa]s in [Enticho Sandstone]

  • Associated soil types
  • * complex of rock outcrops, very stony and very shallow soils
  • * shallow, very stony, silt loamy to loamy soils
  • Inclusions
  • * Shallow, dark loamy soils with a good natural fertility
  • * shallow, stony loam soils

Colluvial">Colluvium">Colluvial slopes at the edge [Enticho Sandstone] plateaus

  • Dominant soil type: sandy clay loams to sands developed on sandy colluvium
  • Associated soil type: shallow, very stony, silt loamy to loamy soils
  • Inclusion: brown, silty loams to loamy sands developed on alluvium, with good natural fertility Fluvisol, Fluvic Cambisol

Undulating plain (Atsbi horst)

  • Associated soil types
  • * complex of rock outcrops, very stony and very shallow soils
  • * shallow, very stony, silt loamy to loamy soils
  • * shallow to moderately deep silt loamy to loamy soils
  • Inclusions
  • * brown, silty loams to loamy sands developed on alluvium, with good natural fertility Fluvisol, Fluvic Cambisol
  • * clays of floodplains with very high watertable with moderate to good natural fertility

Gently rolling topography on Precambrian rock (Atsbi Horst)

  • Associated soil types
  • * shallow, very stony, silt loamy to loamy soils
  • * shallow to moderately deep, well drained, brown-yellow loamy soils
  • Inclusions
  • * moderately deep dark stony clays with good natural fertility
  • * moderately to deep, dark brown to dark greyish soils with strong structure and good natural fertility, but with frequent waterlogging
  • * clays of floodplains with very high watertable with moderate to good natural fertility

Rolling landscape on [Precambrian] rocks (Atsbi horst)

  • Dominant soil type: complex of rock outcrops, very stony and very shallow soils
  • Associated soil types
  • * shallow, very stony, silt loamy to loamy soils
  • * clays of floodplains with very high watertable with moderate to good natural fertility
  • Inclusion: moderately deep, red-brownish, loamy soils with a good natural fertility

Severely incised Precambrian rock

  • Dominant soil type: rock outcrops and very shallow soils
  • Associated soil type: shallow, very stony, silt loamy to loamy soils
  • Inclusion: clays of floodplains with very high watertable with moderate to good natural fertility

Fluvial landscape of Hayqi Mesal

  • Associated soil types
  • * complex of rock outcrops, very stony and very shallow soils
  • * shallow, stony loam soils with moderate fertility
  • * Brown to dark, silty clay loams to loamy sands developed on alluvium, with good natural fertility
  • Inclusions
  • * sandy clay loams to sands developed on sandy colluvium
  • * sandy clay loams to sands developed on sandy colluvium

Des'a forest

  • Associated soil types
  • * shallow, stony, dark, loamy soils on calcaric material
  • * deep, dark cracking clays on calcaric material
  • * dark soils with good developed structure and a very good natural fertility on calcaric material
  • * shallow, dark, stony, loamy soils on calcaric material, rich on organic matter
  • Inclusions
  • * Rock outcrops and very shallow soils on limestone
  • * Shallow very stony loamy soil on limestone
  • * Shallow, dark loamy soils with a good natural fertility
  • * Moderately deep, stony, dark cracking clays on calcaric material

Des'a hills

  • Associated soil types
  • * complex of rock outcrops, very stony and very shallow soils
  • * shallow, very stony, silt loamy to loamy soils
  • * shallow, stony loam soils with moderate fertility
  • Inclusions
  • * moderately deep dark stony clays with good natural fertility
  • * deep dark cracking clays with very good natural fertility, waterlogged during the wet season

Alluvial plains induced by [tufa] dams

  • Dominant soil type: deep dark cracking clays with very good natural fertility, waterlogged during the wet season
  • Associated soil type: stony, dark cracking clays with good natural fertility
  • Inclusions
  • * shallow, stony, dark, loamy soils on calcaric material
  • * shallow, very stony, silt loamy to loamy soils

Polje

  • Associated soil types
  • * Rock outcrops and very shallow soils on limestone
  • * Shallow very stony loamy soil on limestone
  • * Shallow, dark loamy soils with a good natural fertility
  • * deep, dark cracking clays on calcaric material
  • Inclusions
  • * Dark, loamy soils with good developed structure and a very good natural fertility
  • * moderately deep, red-brownish, loamy soils with a good natural fertility
  • * moderately to deep, dark brown to dark greyish soils with strong structure and good natural fertility, but with frequent waterlogging
  • * alluvial clays of flood plains and basins with ponded drainage on calcaric material

Very gently undulating Agula shale

  • Associated soil types
  • * shallow, very stony, silt loamy to loamy soils
  • * moderately deep dark stony clays with good natural fertility
  • * deep, dark cracking clays on calcaric material
  • Inclusion: deep dark cracking clays with very good natural fertility, waterlogged during the wet season

Soil erosion and conservation

The reduced soil protection by vegetation cover, combined with steep slopes and erosive rainfall has led to excessive soil erosion. Nutrients and organic matter were lost and soil depth was reduced. Hence, soil erosion is an important problem, which results in low crop yields and biomass production.
As a response to the strong degradation and thanks to the hard labour of many people in the villages, soil conservation has been carried out on a large scale since the 1980s and especially 1980s; this has curbed rates of soil loss. Measures include the construction of infiltration trenches, stone bunds, check dams, small reservoirs such as Addi Shihu and Era as well as a major biological measure: exclosures in order to allow forest regeneration. On the other hand, it remains difficult to convince farmers to carry out measures within the farmland, such as bed and furrows or zero grazing, as there is a fear for loss of income from the land. Such techniques are however very effective.