Mineralogical and micromorphological characterisation of two soil sequences of the UNZA-FARM(Zambia)
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Date
2011-03-31
Authors
Shitumbanuma, Victor
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Abstract
The land has been the ultimate source of nourishment and
origin of man and other living organisms. Man has depended and
still depends on plants and animals for his survival. These in
turn depend on the earth and other organisms.
The cultivation of crops has been known to man for a long
time, and the use of different techniques to manipulate the soil
and plants has resulted in increased crop production. With the
increased human population, the demand on the land has increased,
and man has to find better and more effective means of utilizing
this now scarce resource of soil.
Various disciplines of science have studied the soil from
different angles, with the ultimate aim of bettering their understanding
of it. As the soil is quite a heterogeneous material,
its study calls for a combined approach of study.
Of the various branches of soil science, a new branch, employing
the aid of microscopic and ultramicroscopic techniques
has emerged. Micropedology, which aims to search for the processes
responsible for the formation of soils as well as specific
features both of natural and artificial origin has become
an important tool in investigating into the genesis, classification
and management of soil.
In this study, which was originally meant to cover two soil
sequences, a soil sequence has been studied, from a mineralogical
and micromorphological view, with the aim of knowing something
about its genesis and management properties.
Routine physical-chemical analyses, micromorphological and
mineralogical analyses were carried out on the soil samples from
profiles on the sequence. It was found that there is a colour
differentiation along the sequence, due to change in drainage
condition. The profiles have been found to have a pellicular to
bridged grain surface horizon, overlying illuvial horizons. This
kind of microstructure is seen to increase with depth downslope,
and this has been attributed partly to the translocation of soil
material downslope. Illuviation of clay with free iron and fine
organic material has been found to be evident in all the profiles
in this sequence. The upper two well drained horizons, have a
granular aggregate microstructure in subsurface horizons which
gives them a good permeability to water and air.
The low land soil, was found to be partly drained and with
a higher content of in situ formed nodules. It was found that
there was a coincidence between the presence of brown spots in
the profile, with the presence of oriented reddish brown clay
coatings.
The soils have been found to be depleted of most weatherable
minerals and to be dominated by resistant, generally nutrient
poor mineral grains. Kaolinite is the most dominant clay mineral,
with mica, being the other constituent. The silt fraction, shows
high amounts of quartz and mica. From the study of heavy minerals
and soil thin sections, the parent material show evidence of
metamorphic origin, and lateritic origin. The soils have been
found to have low CEC and a relatively high amount of iron oxides
The presence of the iron oxides, and kaolinite, with micas, has
been used to explain the observed low CEC.
As regards management properties, it has been found that the
low CEC of these soils may be a limitation to good crop yield.
The low pH of the upland soils may require application of lime
to expect good response from fertilizer application. The low
land soils have been found to have a limitation of aeration
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Keywords
Soil