Pedology at Four Representative Sites of Southern Highland Zone of Tanzania

Johnson Godlove Mtama

doi:10.11648/j.ajaf.20180605.11

Abstract

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. CECsoil 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.

Highlights

The soils, landscapes and landforms of Tanzania are diverse
The pedological perspective of Tanzania is one of tremendous regional and local parent material variation including alluvium and colluvium, volcanic ash, aeolian sands as well as seemingly every type of rock known to geology [1]
The epipedons are generally dark colored while the B horizons are brown to red, which indicates generally well drained conditions

Summary

Introduction

The major terrain features include Mounts Kilimanjaro, Ngorongoro, Rungwe, Meru active and dormant volcanoes, the Great Rift Valley, Udzungwa, Kipengere and Livingstone mountain ranges of varying origins such as tectonic blocks and fold systems, coastal plains, interior plains, tectonic lakes with associated lake plains and terraces. Rufiji, Ruvu, Pangani and Malagalasi rivers, all of which with sizeable floodplains, terraces and delta systems. Each of these features is geomorphically active, resulting in a wide range of local terrain features including alluvial fans, abandoned oxbows, sand dunes, landslide scars and rotational slumps, etc. The pedological perspective of Tanzania is one of tremendous regional and local parent material variation including alluvium and colluvium, volcanic ash, aeolian sands as well as seemingly every type of rock known to geology [1].

Objectives

Methods

Results

Conclusion