Environmental Engineering Reference
In-Depth Information
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effective cation exchange capacity (ECEC)
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organic carbon
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nitrogen
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phosphorus
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potassium.
The levels of these parameters are compared with some standards to indicate
whether the soil is fertile or not. The standards vary with the method used in the
laboratory analyses. A soil which is high in the above parameters is considered
fertile. In order to measure these parameters, soil samples are taken from the
field and conveyed to the laboratory for the analysis. It must be emphasized that
the quality of the results is dependent on the quality of laboratory analysis.
Indirect methods
In addition to the scientific method, which requires routine laboratory analysis,
scientists employ indirect methods in assessing soil fertility by the use of certain
parameters such as colour. A soil that is black or dark in colour may indicate a
high amount of organic matter or humus and high fertility status. A red soil indi-
cates that the soil is well drained, well aerated, and contains ferric oxide. Such
soils are often seen at summits and upper to middle-slope sites. Brown to light
brown soils, often found in the middle to lower-slope sites, are moderately well
drained. Grey or white soils, often found between the lower slopes and the valley
bottoms, are poorly drained and subject to waterlogging.
Some characteristics of sand and clay soils
Sandy soils contain a large number of big pores. Therefore they are well aerated.
Drainage is very good but they are poor in retaining moisture and nutrients. They are
generally considered to be of poor fertility. They require addition of organic manure
and/or mineral fertilizers to make them fertile. They can easily be tilled with
machines. Clay soils are poorly drained and aerated. They have a high capacity to
store water and nutrients, but it is not easy for plants to abstract water from clay soils.
Community approach to measurement of soil fertility and classification
In assessing a natural resource such as soil fertility, a community's main method
is observation. The observation is based on certain parameters such as colour,
indicator plants, micro fauna and wildlife, and land-use stage.
Physical characteristics
In direct observation, farmers use the physical elements of colour, surface char-
acteristics, and texture of the soil in determining soil fertility. The colour of the
soil is used as a basis for clarification. The colours involved are white, black, and
