As a natural resource, soil is of immense value to man. In the agricultural orient the distribution and density of population have conformed to the persisting patterns of soil fertility and productivity.
Soil is basically broken-down rock materials and consists of decomposed rock debris and decayed organic matter(humus) which have been produced by weathering.
According to Arthur Holmes From a geological point of view soil may be defined as the surface layer of the mantle of rock-waste in which the physical and chemical processes of weathering co-operate in intimate association with biological processes (Principles of Physical Geology, Second Edition Completely Revised, the English Language Book Society & Nelson).
Arthur N. Strahler and Alan H. Strahler defines soil as a natural surface layer containing living matter and supporting or capable of supporting plants. (Modern Physical Geography, John Wiley & Sons, Inc., Newyork).
Chester R. Longwell & Richard F. Flint defines soil as-Soil is that part of the regolith that will support rooted plants. (Introduction to Physical Geology, 2nd Edition, John Wiley & Sons, Inc. New York, London). From the above definitions, it may be stated that-
Soil is the surface layer of the earth restricted to land, consisting of a layer of broken-down, fine and loose rock material, produced by the weathering processes, mixed with decayed vegetation and other organic matter.
Soil may be found on top of the parent rock or at some distance from it after transport and supports vegetation.
The science which deals with the study of the soil is known as Pedology and the process of soil formation is called pedogenesis.
The Soil Profile
The pedologists have distinguished a number of layers or horizons within the soil. A vertical