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Soil in Dogu'a Tembien | |
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Stratigraphic range: | |
![]() Mazi-Pellic Vertisol in the Hagere Selam Highlands | |
Type | Soilscape |
Thickness | 2 m (6.6 ft) |
Lithology | |
Primary | Clay, Loam |
Other | Sand, Rocks |
Location | |
Coordinates | 13°30′N39°10′E / 13.5°N 39.16°E |
Region | Tigray |
Country | ![]() |
Extent | Dogu'a Tembien |
The soils of the Dogu'a Tembien woreda (district) in Tigray (Ethiopia) reflect its longstanding agricultural history, highly seasonal rainfall regime, relatively low temperatures, an extremely great variety in lithology (with dominance of basalts and limestone) and steep slopes. Outstanding features in the soilscape are the fertile highland Vertisols and Phaeozems in forests. [1] [2] [3] [4] [5]
Annual rainfall depth is very variable with an average of around 800 mm. [6] 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. [7]
From the higher to the lower locations, the following geological formations are present: [8]
As part of the Ethiopian highlands the land has undergone a rapid tectonic uplift, leading the occurrence of mountain peaks, plateaus, valleys and gorges.
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.
Soil degradation in this district became important when humans started deforestation almost 5000 years ago. [12] [13] Depending on land use history, locations have been exposed in varying degrees to such land degradation.
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. [14] [15] [16] 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.
This land system occurs on the central basalt plateau and adjacent ridges; Hagere Selam is entirely in this land system, which is also predominant in tabias Selam, Mahbere Sillasie, Melfa, Lim'at, Seret, Simret, Mika'el Abiy as well as Arebay.
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 tabias Menachek, Mizan, Aregen and Degol Woyane.
This land system occurs on the steep slopes towards the southwestern lowlands; it occupies large areas of tabias Walta, Simret, Mizan, Aregen, Degol Woyane, Mahbere Sillasie and Haddinnet.
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.
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.
This land system occurs on Antalo Limestone, it is predominant in tabias Walta, Inda Sillasie, Ayninbirkekin, Amanit and Debre Nazret.
This land system occurs on Agula Shale at the east of Dogu'a Tembien, it is predominant in tabias Addi Azmera, Mizane Birhan and parts of Debre Nazret, Haddinnet and Addilal.
This land system occurs on Antalo Limestone; it is predominant in tabias Emni Ankelalu and Addilal.
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.
The reduced soil protection by vegetation cover, combined with steep slopes and erosive rainfall has led to excessive soil erosion. [12] [17] [18] 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. [19] [20] 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. [21] [22]
Measures include the construction of infiltration trenches, stone bunds, [23] check dams, [24] small reservoirs such as Chini and May Leiba as well as a major biological measure: exclosures in order to allow forest regeneration. [3] On the other hand, it remains difficult to convince farmers to carry out measures within the farmland (in situ soil management), 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. [25]