The soils of the Dogu’a Tembienworeda in Tigray reflect its longstanding agricultural history, highly seasonal rainfall regime, relatively low temperatures, an extremely great variety in lithology and steep slopes. Outstanding features in the soilscape are the fertile highland Vertisols and Phaeozems in forests.
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 Hagere Selam is 16.8 °C, oscillating between average daily minimum of 9.3 °C and maximum of 24.1 °C. The contrasts between day and night air temperatures are much larger than seasonal contrasts.
Geology
From the higher to the lower locations, the following geological formations are present:
As part of the Ethiopian highlands the land has undergone a rapid tectonic uplift, leading the occurrence of mountain peaks, 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 and a few inaccessible places. 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.
* Rock outcrops and very shallow soils on limestone
* Moderately deep, stony, dark cracking clays on calcaric material
* Deep dark cracking clays with very good natural fertility, waterlogged during the wet season
* Shallow stony dark loams on calcaric material
* Brown loamy soils on basalt with good natural fertility
Gallery: soil profiles in the Hagere Selam Highlands
Basalt plateau
This land system occurs on the westernmost ridges of Dogu’a Tembien, where basalt is overlying Adigrat Sandstone without intervening Antalo Limestone; it is predominant in tabiasMenachek, Mizan, Aregen and Degol Woyane.
Associated soil types
* shallow, very stony, loamy soils
* deep, very dark clays with strong structure and very good natural fertility, temporarily waterlogged during the wet season
* moderately deep, brown, loamy soils with a good natural fertility
Inclusions
* complex of rock outcrops, very stony and very shallow soils
This land system occurs on the steep slopes towards the southwestern lowlands; it occupies large areas of tabiasWalta, Simret, Mizan, Aregen, Degol Woyane, Mahbere Sillasie and Haddinnet.
Associated soil types
* complex of rock outcrops, very stony and very shallow soils
* shallow, dry soils with very high amounts of stones
* deep, dark cracking clays with good fertility, but problems of waterlogging
* soils with stagnating water due to an abrupt textural change such as sand over clay
Alluvial plain of Giba River
This land system occurs in Kemishana at the southwestern side of Dogu’a Tembien, where the Giba River gorge widens up when entering into the Abergele lowlands.
Associated soil types
*deep dark cracking clays with very good natural fertility, waterlogged during the wet season
* brown loamy sands developed on alluvium along Giba River
Strongly incised Giba gorge
This land system occurs on in the deeply incised gorge of Giba River, at the lower side of tabias Walta, Inda Sillasie, Amanit and Debre Nazret.
Dominant soil type: complex of rock outcrops, very stony and very shallow soils
Associated soil types
* shallow, stony, dark, loamy soils on calcaric material
* shallow, stony to sandy loam soils on calcaric material
* brown loamy sands developed on alluvium along Giba River
Gently rolling [Antalo Limestone] plateau, holding cliffs and valley bottoms
This land system occurs on Antalo Limestone, it is predominant in tabias Walta, Inda Sillasie, Ayninbirkekin, Amanit and Debre Nazret.
Associated soil types
* shallow stony soils with a dark surface horizon overlying calcaric material
* moderately deep dark stony clays with good natural fertility
* deep, dark cracking clays on calcaric material
Inclusions
* Rock outcrops and very shallow soils
* Shallow very stony loamy soil on limestone
* Deep dark cracking clays with very good natural fertility, waterlogged during the wet season
This land system occurs on Agula Shale at the east of Dogu’a Tembien, it is predominant in tabiasAddi Azmera, Mizane Birhan and parts of Debre Nazret, Haddinnet and Addilal.
Dominant soil type: stony, dark cracking clays with good natural fertility
Associated soil types
* rock outcrops, stony and shallow soils
* red-brownish loamy soils with good natural fertility
Inclusions
* deep, dark cracking clays on calcaric material with good fertility but poor drainage
Incised Giba plateau, upstream of (future) [Lake Giba]
This land system occurs on Antalo Limestone ; it is predominant in tabiasEmni Ankelalu and Addilal.
Associated soil types
* complex of rock outcrops, very stony and very shallow soils
* shallow, stony, dark, loamy soils on calcaric material
* shallow to very shallow, very stony, loamy soils
Inclusions
* Shallow, stony loam soils with moderate fertility
* Deep, dark cracking clays with good fertility, but problems of waterlogging
* Brown to dark, silty clay loams to loamy sands developed on alluvium, with good natural fertility
This land system occurs where the Giba valley widens; it occurs only at the lower places of tabia Emni Ankelalu and will be flooded once the Lake Giba reservoir will be filled.
Associated soil types
* complex of rock outcrops, very stony and very shallow soils
* shallow, stony, dark, loamy soils on calcaric material
* shallow, very stony, silt loamy to loamy soils
Inclusions
* moderately deep dark stony clays with good natural fertility
* Brown, silty loams to loamy sands developed on alluvium, with good natural fertility Fluvisol, Fluvic Cambisol
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 Chini and May Leiba 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.
