Saturday, 15 July 2006

Soil Geomorphology:Concept, Theory and Practices.

Daniel Bitire, Univ of Agriculture Abeokuta Nigeria, 11 Olaoluwa St Ojodu Ikeja Lagos, P.O Box1247 Sapon Abeokuta Ogun, Lagos, Nigeria

The concept of soil geomorphology relies heavily on the summary and assessment,as weathering progresses,soil become reduced, in the sense that there is a reduction in it's average particle size. the potiential mobility of the soil increases as the particle size decreases and all reduced material above a local base level is metastable i.e vulnerable to removal.The maximum rate of natural denudation is the rate at which surface material which is almost but not quite mobile,becomes mobile,furthermore on any particular gradient there is a degree of reduction beyond which soil is too mobile to remail in the development of the landscape will be a function of this metastability of the soil,which is a function of the ease with which soil is detached and transported.Also the landscape development depends on the metastablility of the particular site which is a function of slope gradient and proximity to the next major break or change of slope on the slope profile.An encroaching pediment will therefore affect the soil on the upper surface long before that soil is affected physically by erosion.However analysis has shown that the relationship between gradient and degree of reduction applies only to those part of a slope on which there is no accumulation of transported material.The theory of soil geomorphology deals with the arrangement of landforms and the processes that have been or are shaping them geomorphological process may create disstinctive landforms such as erosion surfaces,which have a great influnce on soil type and superficial material in harness which is of greatest significance.Investigation of how landforms develop and of rates and result of processes has relied on the study of surfaces and sediments.But soils that have developed on geomorphic surfaces during and after surface stabilization have the potiential to record more accurately the history of landscape development.Soil is the collection of natural bodies on the earth surface, in places modified or even made by man of earthy materials, containing living matter and supporting plant out-of-doors it upper limit is air or shallow water. In soil geomorphological classification both the charateristic of the parent material and climate, affect the type of soil formed.within any climatic regiom differences in soil properties are greatly affected by differences in parent material in view of the fact that climatic differences occur within the tropics and topographical features mark or enhance the micro climatic enviroment and in view of age differences in land surfaces,soils are usually more conviniently studied and classified terms of profile.A profile represents the soil at any one spot and the morphology of each soil such as colour,texture,structure etc as expressed in it's profile reflect the combined effects of the particular set of genetic factor responsible for it's developmen.The difficulty with soil classification is that soil often have no definite individual boundaries.soil stratigraphy in general sense, the record of event leading to the development of an organic deposits and it's associated soils is preserved within the deposits and soil themselves. changing conditions during the evolution of a deposits commonly produce a series of layers of horizons which may be distinguish from one another on the basis of biological composition of identifiable plant remains, decomposition rate of organic material presence or absence of wood or charcoal, amount and distribution of mineral material,and presence or absence of shells and other faunal remains such as bones or tusk further information can be gained by more sophisticated analysis in which the chemical and physical characteristic of the organic and mineral horizons are often determined.The distribution of trace element and heavy metals the kind of pollen grains and microfossils content are important. The history of and organic deposits may be inferred from cross sections which are developed from information obtained by numerous boring.Cylindrical cores of the deposited material are removed and each layer in the deposit are describe in details. The spacing of the boring is determined principally by the amount of the variation in the composition thickness or sequence of horizons(stratigraphy)from core to core.

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