Soil Factor – Parent Material
The unconsolidated mass from the soils are formed is the parent material. It constitutes the basic mineral framework of most soils and consists of small fragments of inorganic matter which has been derived from solid rock by mechanical or chemical types of weathering,
Depending on the mode of origin, most parent materials can be classified as: residual parent material and transported parent material.
Residual Parent Material – Rocks
Rocks are residual or in-place parent material. The composition of rocks determines the chemical composition of the soil. The rocks may be:
Igneous Rocks, formed when a hot mixture of elements called magma cools. These may be present above or below the surface of the earth.
Sedimentary Rocks, formed by the material deposited in lakes and oceans. Over time and under the pressure of overlying materials, layers of these accumulated sediments consolidate into rocks. Over geological time, these rocks have been exposed by uplift and wearing away of mountains. The examples are shale and limestone
Metamorphic Rocks, formed when either igneous rocks or sedimentary rocks are heated or subjected to intense pressure at considerable depths within earth. The Original minerals melt and form new minerals. The common examples are slate and marble.
Transported Parent Material
The transported parent materials are derived from mineral particles which have been brought from their place of origin by various agents such as wind, water, glaciers, and gravity. The soils developed from transported material are commonly more fertile than soils derived from in-place parent material because of the diversity of materials.
On the basis of transportation agencies, the transported material Can be subdivided into: colluvial (by gravity), alluvial (by water), glacial (by ice), and eolian (by wind).
Colluvial Transportation by Gravity (Colluvial Soil)
colluvial parent materials are moved by the pull of gravity and are composed of fragments of rocks detached from the heights above and carried down the slopes. The material deposited is known as talus. Colluvial parent materials are restricted to mountainous regions and most hillside deposits (slopes or cliffs) are colluvial.
Colluvial parent material consists of coarse and stony fragments the soils developed from colluvial materials are not of great agricultural Importance because of unfavorable physical and chemical characteristics. The colluvial deposits are without stratification.
Alluvial Transportation by Water (Alluvial Soil)
The parent materiel deposited by running water is termed as alluvial. There are general classes of alluvial deposits: floodplains, delta deposits and alluvial fans.
Floodplain IS the part of the valley inundated during floods. The floodplains provide significant parent materials for other important soil areas. The soils derived from these sediments are generally rich in nutrients and productive.
Delta Deposits are the deposits near the mouth of the river. Where streams enter a river or the sea the suspended material (silt and clay) settle out near the mouth of river forming a delta. A delta is continuation of a floodplain, clayey in nature and soils originating from such parent material are fertile and productive from agricultural point of view.
Alluvial Fans are formed when streams leave a narrow valley in a mountainous area and suddenly descend to a much broader valley below deposit sediment in the shape of a fan. Fan material contains gravel and stone, somewhat porous and well drained, Alluvial fan deposits are found in mountainous and hilly areas.
Eolian Transportation by Wind (Eolian Soil)
The Wind transported parent material is termed eolian. It is classed either as dune or loess (luss). Winter conditions are suitable for transport of material by wind.
Sand Dunes: Sand dunes are found along the shores of seas and lakes, along river valleys and in dry regions. Water currents erode and deposit the sand particles snores, banks or upon floodplains which is moved by wind onto the land upon. In dry regions weathering of sandstone and other rocks may produce sand blown and deposited as dunes. Sahara Desert is famous for its sand dunes. Dune sand is composed of particles of nearly uniform size and chemical composition.
Loess (Pronounced Luss): The windblown materials, comprised primarily of silt with some fine sand and clay are called loess. The material is derived from rock deposited by the melt waters of glaciers then blown onto plans.
Glacial Transportation by Glaciers (Glacial soil)
The materials deposited directly by the ice are called glacial till, and materials of glacial origin whether deposited by the ice or associated waters is called drift. The glacial till comprises of particles of all sizes from clay to boulders that are thoroughly mixed without any kind of sorting. Glacial till is found mostly as irregular deposits caned moraines. An outwash stream is formed by streams that are heavily laden with glacial sediment flowing from the ice. The outwash plain consists of sand and gravel usually and found in valleys and plains where glacial waters are able to flow away freely. When the ice front came to a standstill where there was no escape for the water, ponding began and ultimately very large lakes were forms. Such lakes are called glacial lakes.
Types of Soils on the Basis of Parent Material
The terms designating the parent material are also applied to the soils that occur on these deposits, for example residual soils, colluvial soils, glacial soils, alluvial soils and eolian soils.