The soils of the Dogu’a Tembienworeda (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]
Factors contributing to soil diversity
Climate
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]
Geology
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.
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.[12][13] 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.[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.
Hagere Selam Highlands
Typical catena in the Hagere Selam highlandsLuvisol in Dingilet
complex of rock outcrops, very stony and very shallow soils ((Lithic) Leptosol) (1)
shallow, stony sandy [[loam soils (Eutric Regosol and Cambisol) (21)
Inclusions
shallow, dry soils with very high amounts of stones (Leptic and Skeletic Cambisol and Regosol) (4)
deep, dark cracking clays with good fertility, but problems of waterlogging (Chromic and Pellic Vertisol) (12)
soils with stagnating water due to an abrupt textural change such as sand over clay (Haplic Planosol]]) (34)
Alluvial plain of Giba River
Typical catena in the alluvial plain of Giba River at the edge of AbergeleAt Kemishana, the Giba River leaves its gorge and enters in the alluvial plain
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 (Chromic Vertisol, Pellic Vertisol) (12)
brown loamy sands developed on alluvium along Giba River (Fluvisol) (30)
Strongly incised Giba gorge
Typical catena in the severely incised Giba gorgeSlopes of the Giba gorge at Addi Lihtsi, with incense trees
complex of rock outcrops, very stony and very shallow soils ((Lithic) Leptosol) (1)
shallow, stony, dark, loamy soils on calcaric material (Rendzic Leptosol) (3)
shallow to very shallow, very stony, loamy soils (Skeletic/Leptic Cambisol and Regosol) (4)
Inclusions
Shallow, stony loam soils with moderate fertility (Eutric Regosol and Cambisol) (21)
Deep, dark cracking clays with good fertility, but problems of waterlogging (Chromic and Pellic Vertisol) (12)
Brown to dark, silty clay loams to loamy sands developed on alluvium, with good natural fertility (Fluvisol) (30)
Giba wide valley bottom
Typical catena in the Giba wide valley bottom The Giba wide valley bottom
This land system occurs where the Giba valley widens; it occurs only at the lower places of tabiaEmni 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 ((Lithic) Leptosol) (1)
shallow, stony, dark, loamy soils on calcaric material (Rendzic Leptosol) (3)
shallow, very stony, silt loamy to loamy soils (Skeletic Cambisol, Leptic Cambisol, Skeletic Regosol) (4)
Inclusions
moderately deep dark stony clays with good natural fertility (Vertic Cambisol) (10)
Brown, silty loams to loamy sands developed on alluvium, with good natural fertility (Mollic) Fluvisol, Fluvic Cambisol (29)
Soil erosion and conservation
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 situsoil 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]
^Nyssen, J.; Naudts, J.; De Geyndt, K.; Haile, Mitiku; Poesen, J.; Moeyersons, J.; Deckers, J. (2008). "Soils and land use in the Tigray highlands (Northern Ethiopia)". Palaeogeography, Palaeoclimatology, Palaeoecology. 19 (3): 257–274. doi:10.1002/ldr.840. S2CID128492271.
^Van de Wauw, J. and colleagues (2008). "Soil-landscape relationships in the basalt-dominated highlands of Tigay, Ethiopia". Catena. 75: 117–127. doi:10.1016/j.catena.2008.04.006.
^Hunting Technical Services. Central Tigre Development Study – Tigre Province Ethiopia, Working Paper I: Soils and land classification. Hemel Hempstead (U.K.): Hunting Technical Services Ltd.
^Bosellini, A.; Russo, A.; Fantozzi, P.; Assefa, G.; Tadesse, S. (1997). "The Mesozoic succession of the Mekelle Outlier (Tigrai Province, Ethiopia)". Mem. Sci. Geol. 49: 95–116.
^Tefera, M.; Chernet, T.; Haro, W. Geological Map of Ethiopia (1:2,000,000). Addis Ababa, Ethiopia: Ethiopian Institute of Geological Survey.
^Moeyersons, J. and colleagues (2006). "Age and backfill/overfill stratigraphy of two tufa dams, Tigray Highlands, Ethiopia: Evidence for Late Pleistocene and Holocene wet conditions". Palaeogeography, Palaeoclimatology, Palaeoecology. 230 (1–2): 162–178. Bibcode:2006PPP...230..165M. doi:10.1016/j.palaeo.2005.07.013.
^ abNyssen, Jan; Poesen, Jean; Moeyersons, Jan; Deckers, Jozef; Haile, Mitiku; Lang, Andreas (2004). "Human impact on the environment in the Ethiopian and Eritrean highlands - a state of the art". Earth-Science Reviews. 64 (3–4): 273–320. Bibcode:2004ESRv...64..273N. doi:10.1016/S0012-8252(03)00078-3.
^"Principes de la cartographie des pédopaysages dans les Alpes". Écologie. 29 (1–2): 49. 1998. ProQuest223074690.
^Tielens, Sander (2012). Towards a soil map of the Geba catchment using benchmark soils. MSc thesis. Leuven, Belgium: K.U.Leuven.
^Demel Teketay (2001). "Deforestation, wood famine, and environmental degradation in Ethiopia's highland ecosystems: urgent need for action". Northeast African Studies. 8 (1): 53–76. doi:10.1353/nas.2005.0020. JSTOR41931355. S2CID145550500.
^Nyssen, Jan; Frankl, Amaury; Zenebe, Amanuel; Deckers, Jozef; Poesen, Jean (2015). "Land management in the northern Ethiopian highlands: local and global perspectives; past, present and future". Land Degradation & Development. 26 (7): 759–794. doi:10.1002/ldr.2336. S2CID129501591.
^Vancampenhout, K. and colleagues (2019). Sheet and Rill Erosion and Its Control: Lessons from Dogu'a Tembien. In: Geo-trekking in Ethiopia's Tropical Mountains — The Dogu'a Tembien District. SpringerNature. doi:10.1007/978-3-030-04955-3_21. ISBN978-3-030-04954-6. S2CID199110301.
^Nyssen, J.; Veyret-Picot, M.; Poesen, J.; Moeyersons, J.; Haile, Mitiku; Deckers, J.; Govers, G. (2004). "The effectiveness of loose rock check dams for gully control in Tigray, Northern Ethiopia". Soil Use and Management. 20: 55–64. doi:10.1111/j.1475-2743.2004.tb00337.x. S2CID98547102.
^Tewodros Gebreegziabher, and colleagues (2009). "Contour furrows for in situ soil and water conservation, Tigray, Northern Ethiopia". Soil and Tillage Research. 103 (2): 257–264. doi:10.1016/j.still.2008.05.021.
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