Geomorphology and Soil Properties at the Middle and Lower Eastern Clay Plains - Nuba Mountains. South Kordofan, Sudan

This research study aimed to describe the geomorphology and characterize the soil properties at the middle and lower clay plains located at the eastern parts of Nuba Mountains, Sudan. Soil samples were collected from nineprofile pits alonga transect stretching from Abbasyia to Megenis through Terter (64 Km). The area is a broad, slightly sloping to undulating upland clay plains. The plains are dissected by Khors and Wadis (Khor and Wadi are water course in Arabic language) draining the Nuba Mountains hilly area, numoures low ridges (viens and dykes) separated by shallow depressions running through the area. The majority of the soils identified belong to the dark cracking clays. The soils are formed insitu and on colluviums and alluvium derived from basement complex rocks. The origin of these clays is thought to belong to Quarternary alluvial deposits probably similar in time to other dark cracking clays of central Sudan but but under different forming processes (Showgi et al 2016). These deposits form well developed Vertisols (Pacheco and Dawoud, 1976, Ahmed 1983, Abedine and Robibson 1970). Wide cracking, gilgae microrelief and very dark grayish colours dominate the surfaces. Topsoil structure has loose granular mulch, the subsoil has subangular blocky structure, below that the structure is massive. Subsoil and substrata layers have parallelepiped and wedge shaped structure aggregates. Slickensides was also observed in all profiles, reflecting expansion and contraction upon wetting and drying of the soil. Fine and medium tubular pores, small and large whitish irregular CaCO3 concretions were noted. Fine and medium sand grains and polished quartz pebble arecommon. The soil reaction is slightly alkaline in all profilesincreasing with depth. The sois are non saline and nonesodicon middle plains but mildly sodic and sodic at lower plains. Cation exchange capacity is high at top horizons and very high below indicating presence of illiticand montmorillonitic clay minerals. Sodium Adsorption Ratio (SAR) is lowand the soilsare non - calcareous with low amount of CaCO3. Organic matter is low decreasing with depth and the total nitrogen is also low. Nutrient status expressed as extractable cations meq/100 g soil is generally high Soil texture is clay throughout the profile and clay content increases with depth. The bulk density (BD) is high increasing with depth, and porosity results coincidewith bulk density trend. Although most of the cracking clay soils in Sudan are sharing similar origin (basaltic igneous materials) but their subsequent depositional processes, landscape geomorphology and local climate have affected their mineralogical, physical and chemical properties. This applies to the clay plains of Nuba Mountains as most soils are characterized by lower CEC, mild alkalinity and low calcium carbonate content.