Soil Biologically active porous medium that has developed

Soil Biologically active, porous medium that has developed in the upper most layer of earth’s crust

Regolith & Parent Material • The loosely arranged geological material present below the soil and above the rocks is called regolith • Parent Material • The upper part of regolith is called parent material. It is the basic inorganic framework of the soil into which organic matter, living organisms, water and gases incorporated. • The upper 1 -2 meters of regolith is rich in organic matter because plant roots concentrate there and is subjected to more weathering. The products of weathering give rise to characteristics layering called horizons

Profile of Soil • Horizons of Soils • O) Organic surface layer: Layer of plant remains, the upper part often relatively undecomposed, but the lower part may be strongly humified. • A) Surface soil: Layer of mineral soil with most organic matter accumulation and soil life. • Additionally, due to weathering, oxides (mainly iron oxides) and clay minerals are formed and accumulated.

Conti… • B) Subsoil: This layer has normally less organic matter than the A horizon, so its colour is mainly derived from iron oxides. Iron oxides and clay minerals accumulate as a result of weathering. • In a soil, where substances move down from the topsoil, this is the layer, where they accumulate. The process of accumulation of clay minerals, iron, aluminium and organic compounds, is referred to as illuviation.

Conti… • C) Substratum: Layer of poorly weathered or unweathered rocks. This layer may accumulate the more soluble compounds like Ca. CO 3. • R) Bedrock: R horizons denote the layer of partially weathered or unweathered bedrock at the base of the soil profile. • Unlike the above layers, R horizons largely comprise continuous masses of solid rock that cannot be dig out by hand.

Horizons

Soil Genesis/Soil Formation • Parent Material • Depending on the mode of origin, most parent materials can be classified as residual parent and transported parent material • Residual Parent Material • Rocks are residual parent material. The composition of rocks determines the chemical composition of the soil.

Residual Parent Material • They rocks may be: • 1. Igneous rocks • Formed when a hot mixture of elements called magma cools. These may be present above or below the surface of earth • 2. Sedimentary rocks • Formed by the material deposited in lakes and oceans. Over time and under the pressure of overlying materials, layers of the accumulated sediments change into rocks. Examples shale and limestone.

3. Metamorphic rocks • Formed when either igneous rocks or sedimentary rocks are heated or subjected to intense pressure at considerable depths within earth. The original materials melt and form new minerals. The common examples are slate and marble

Transported Parent Materials • The transported parent materials are derived from minerals 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 materials are commonly more fertile than soils derived from in-place parent materials because of diversity of materials.

Types of Transported Parent Materials • Colluvial- Transportation by Gravity (Colluvial Soil) Colluvial materials are moved by the pull of gravity and are composed of fragments of rocks detached from heights above and carried down the slopes. The material deposited is known as talus.

Alluvial Soil • Alluvial-Transportation by Water • The parent material deposited by running water is termed alluvial. There are three general classes of alluvial deposits • Floodplain is the part of valley supplied water during floods. The floodplains provide significant parent materials for other important soil areas • The soil derived from these sediments are generally rich in nutrients and productive.

Alluvial…. • Delta deposits are the deposits near the mouth of the river. • Delta When river/streams enter a sea, the suspended materials settle out near the mouth of river forming a delta. • Soils originating from such parent material are fertile and productive from agricultural point of view.

Alluvial…. • Alluvial fans are formed when streams leave a narrow region in a mountainous area and suddenly descend to a much broader region below deposit sediment in the shape of a fan. • Fan material contains gravel and stone.

Eolian Soil • Eolian-Transportation by wind • The wind transported parent material is termed eolian. It is classified either as dune or loess. • Sand dunes are found along the shores of seas and lakes. Dune sand is composed of particles of nearly uniform size and chemical composition. • Loess The wind blown materials, composed of silt with some fine sand clay are called loess.

Glacial Soil • Glacial- Transportation by glaciers • The materials deposited directly by ice are called glacial till, and materials of glacial origin whether deposited by ice, or associated waters is called drift.

Physical and chemical nature of soil separates • Gravels range in size from 2 mm upward and may be almost rounded, irregularly angular or even flat. These are composed of minerals. • Sand (2 -0. 05 mm average particle diameter) may be rounded or quite irregular depending on the amount of abrasion that they have received. Sand particles are often fragments of rocks a well as minerals.

Physical and chemical nature of soil separates • Silts • The silt particles range from 0. 05 to 0. 002 mm. non-uniform in shape. Silt particles contain sufficient amount of inorganic and organic nutrients, therefore make the soil fertile. • Clay • The smallest mineral particles are clay fraction of soil that is less than 0. 002 mm in diameter. Clay particles generally are highly plastic when moist. When clay is wetted it tends to be sticky and is easily moulded.