Variations in Soils and their Mineralogy in the Kulubi Area,Harar, Ethiopia
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Date
1981-07
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Addis Ababa Universty
Abstract
The geology, geomorphology and soils of the Kulubi area,
in eastern Ethiopia, are described.
The succession of rocks in the region comprises Precambrian
rocks consisting of gneisses, granites, and raigraatit - es overlain
by a trachyte flow; Lower Sandstone Unit (Triassic to Lower
Jurassic) consisting of a lov/er arenaceous and an upper calca-^
reous sub-units; Limestone Unit (Lower Jurassic to Middle-Cretaceous)
consisting of sandy and fossiliferous carbonate rocks;
Upper Sandstone Unit (Middle Cretaceous) consisting of a crossbedded,
parallel-bedded, calcareous, and massive and laminated
sub-units with Mesozoic volcanic intercalations; Tertiary basalts
and Quaternary sediments.,
The three stages in the geomorphological evolution of the
area include a Late Cretaceous-early Cenozoic peneplatation;
Trappean tectonics and formation of basin-plains; and renewed
erosion associated with the rift tectonics*
The major soils in the region are Vertisols, Entisols, and
Mollisols.
The Vertisols occupy depressions in alluvial plains and
scattered spots on Hie'uplands and are developed on basalt and
alluvium. They are ddep, clayey soils with low chromas and
values. Chemically, they are very slightly alkaline, very low
to medium- .in organic matter, low in total nitrogen, and very
low to low in phosphorous. These are the least productive
soils.The Entisols occur on alluvium and on steep slopes of basalts,
sandstones and gneisses.
r
They are dark grayish and reddish brown, shallow and discontinuous,
loamy soils. They are slightly acid to very slightly
alkaline, low to medium in organic matter and total nitrogen,
and medium to high in phosphorous. Their occurrence
on either actively eroding or flooding surfaces significantly
reduces their agricultural productivity.
The Idollisols are the dominant soils occupying flat to
gentle slopes on all theparent materials excepting the basalt.
Those are brownish-blaclc and reddish-brown, shallow to deep,
clay, clay loam, and sandy clay loam soils. They are strongly
acid to slightly alkaline. The organic matter and available
phosphorous contents differ widely. They have a low to medium
total nitrogen. These are the most productive soils.
Comparison of these soils in terms of their textures, pHs,
and organic-matter contents indicates that topography is the
main soil-forming factor controlling the morphological, physical,
and chemical properties of these soils.
Description
Keywords
Geomorphology and soils