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To study the soils of Southern Highland Zone of Tanzania, four representative pedons of some landscapes were
characterized. Their names and identifiers are Seatondale, Mbimba, Inyala, and Uyole, respectively TzSea 01, TzMb 02, TzIny
03, and TzUy04. The pedons were formed from the weathering of among other materials, colluvial igneous rocks, alluvium,
eluvial soils, laterite, lacustrine sands and silts, andesite, pumice, aeolian deposits, and metamorphic rocks including coarse
grained and strongly foliated biotite gneisses. Twenty soil samples were taken for laboratory characterization. In addition to
classical horizon by horizon descriptions and laboratory analyses, 12 core samples were taken for soil-water retention
characterization. The available water holding capacity was rated as very low to low. Pedon descriptions and particle size
analysis showed clay eluviation-illuviation was the predominant pedogenic process in all pedons. Soil pH was rated slightly
acidic to slightly alkaline. Available P ranged from 0.71 mg/kg at Mbimba to 10.67 mg/kg at Seatondale. Exchangeable bases
were variable across and within the profiles; at Uyole and Inyala they were high, while at Seatondale and Mbimba they were
low and medium. Values of exchangeable bases showed decreasing trends with profile depths in all sites. C/N ratios ranged
between 6 and 18, total nitrogen was rated very low to low in both A and B horizons. CEC soil ranged between 17.2 and 36.4
cmol (+) /kg. Organic carbon ranged from very low to high. The soils apparently developed from extreme and moderate
weathering of parent materials. According to the USDA Soil Taxonomy, the pedons classified as Fine, Illitic, Active,
Isothermic Typic Hapludult; Fine, Illitic, Active, Isothermic Andic Paleudalf; Fine, Illitic, Active, Isothermic, Mollic Paleudalf;
Pumiceous, Mixed, Superactive, Isothermic, Typic Hapludand for Seatondale, Mbimba, Inyala, and Uyole, respectively. The
soil depths were deep and very deep. Moisture stress and low levels of some macro-elements highly limited the productivity of
the soils. |
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