Pedological Characterization of the Soils of Atbara and Gash Rivers Upper Atbara Project Area (Kassala State - Sudan)
The soil study area is composed of wide and nearly flat alluvium plain deposits laid by Atbara and Gash Rivers. The study area makes about 751,290 ha and lies within arid and semi-desert climate zones and experiences rainfall in the order of 100 mm in its northern edge, increasing to some 400mm at its southern boundary close to Kassala and east of New Halfa town. The soil study was based mainly on a semi-detailed level soil surveys and the key specifications are a field density of 1 observation each 150 ha. Previously published soil study information was reviewed and incorporated in the findings [5[; ; .
The Aridisols and Entisols in eastern region of Sudan have high potential for crop production, but some constraints emerge affecting crop performance and decreasing yields. Those limitations are aspects of climatic conditions, parent materials and topography manifested generally in, 1) soil moisture deficiency and locally in; 2) accumulation of secondary salts 3) clayey topsoil textures. Aridisols are the soils of arid regions that exhibit at least some subsurface horizon development. They are characterized by being dry most of the year and limited leaching. Aridisols contain subsurface horizons in which clays, calcium carbonate, silica, salts, and/or gypsum have accumulated. Aridisols in their natural state are used mainly for range, wildlife, and recreation. Because of the dry climate in which they are found, they are not used for agricultural production unless irrigation water is available. Entisols formed by rapid deposition on floodplains are universally favored for growing food crops in large part because of the influx of fertility in the deposited material, their level topography, and often the proximity to transportation and water afforded by adjacent rivers. In aridic (torric) soil moisture regimes their alluvial deposits close to rivers are more easily irrigated than associated soils on adjacent higher terraces or the far away finer clayey deposits.
Many, if not most of these areas are subject to flooding and often have extremely abrupt textural differences (i.e. stratifications) engendered by sedimentation processes. In floodplains the river channels migrate as the watershed characteristics change leaving sandy and silty sediments (levees) near the riverbank and finer textured materials further from the riverbank. In aridic moisture conditions Entisols on depressional areas or at higher terraces close to Aridisols are subject to salt accumulation similar to Aridisols. To minimize the concurrence of hazards in Aridisols and Entisols, management procedures should adhere to land and crop management systems. As well, the fertility status is likely to decline due to intensive farming of some nutrient-depleting crops, but this nutrient deficiency is correctable through implementing a fertilizer programme. In the study area, some parameters are management-factors determining e.g. topsoil textures and flat slope favoring uniform distribution of irrigation water through well designed irrigation and drainage network. Those technical inputs if properly used and practiced are expected to sustain crop production.
Key words: Aridisols, Entisols, Atbara and Gash Rivers, Alluvium deposits
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