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Mineralogy of the Major Soils of the Gezira Scheme (Sudan)¹

ABSTRACT

The major soil series comprising the Gezira scheme are Hosh, Suleimi, and Laota. These soils are calcareous, dark brown to grayish brown clays with low organic matter contents (< 1%). The mineralogical properties of these soils were studied by X-ray diffraction (XRD), dissolution, and Ca/Mg and K/NH₄ cation exchange capacities. Some complementary data were obtained using infrared (IR) spectroscopy. The results of the study reveal that these soils have similar sand, silt, and clay mineralogy. The sand fractions are composed of quartz, plagioclase, K feldspars, anatase, and amphiboles. The silt fractions contain, in addition to the above minerals, kaolinite, mica, and chlorite. The coarse clay is composed of chlorite, kaolinite, smectite, plagioclase and K-feldspars, quartz, and mica. The fine clay is predominantly smectite (a mixture of montmorillonite and beidellite), kaolinite, and mica. Calcite is the dominant mineral in the gray hard nodules. The uniform physiographic position and similar mineralogy of these soils suggest that they have a common origin. The similarity in mineralogical composition to that of the recent sediments of the Blue Nile and its tributaries, supports the contention that the Gezira soils have inherited their mineralogical properties from the source area of the sediments in Ethiopia.

¹ Contribution from the Texas Agric. Exp. Stn., Texas A&M Univ., College Station, TX 77843.

² Former Graduate Research Assistant, present address: Dep. of Soil Science, Univ. of Gezira-Sudan. Associate Professor and Professor, respectively, Soil and Crop Science Dep., Texas A&M Univ., College Station, TX 77843.

Received for publication June 29, 1982. Accepted for publication June 2, 1983.