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Soil Formation, Composition and Classification

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Al-Rayan Awis

on 9 October 2012

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Transcript of Soil Formation, Composition and Classification

Soil Formation, Composition and Classification - the loose material that covers the land surfaces of Earth and supports the growth of plants. Soil: - a loose mixture of rock fragments and organic materials that can support the growth of vegetation. - an ongoing process that proceeds through the combined effects of five soil-forming factors: parent material, climate, living organisms, topography, and time. Soil Formation: - Each combination of the five factors produces a unique type of soil that can be identified by its characteristic layers, called horizons. - also known as pedogenesis (from the Greek words pedon, for “ground,” and genesis, meaning “birth” or “origin”). Bedrock itself does not directly give rise to soil. Rather, the gradual weathering of bedrock, through physical and chemical processes, produces a layer of rock debris called regolith. Roughly 99 percent of the world's soils derive from mineral-based parent materials that are the result of weathering, the physical disintegration and chemical decomposition of exposed bedrock. The characteristics of soil depend mainly on the rock from which the soil was weathered, which is called the soil's parent rock. Water, ice, wind, heat, and cold cause physical weathering by loosening and breaking up rocks.

Climate also determines the speed at which parent materials undergo chemical weathering, a process in which existing minerals are broken down into new mineral components.

Climate also influences the developing soil by determining the types of plant growth that occur. Topography, or relief, is another important factor in soil formation. The degree of slope on which a soil forms helps to determine how much rainfall will run off the surface and how much will be retained by the soil. The amount of time a soil requires to develop varies widely according to the action of the other soil-forming factors. humus:
a dark-brown organic component of soil that is derived from decomposed plant and animal remains and animal excrement. horizon:
a horizontal layer of soil that can be distinguished from the layers above and below it; also a boundary between two rock layers that have different physical properties. A horizon or topsoil:
the upper fertile layer of soil, from which plant roots take nutrients; a mixture of organic materials and small rock particles.

B horizon or subsoil:
the compacted soil beneath the topsoil; contains minerals leached from topsoil, clay, or sometimes humus.

C horizon:
partially altered parent material.

E horizon:
a layer from which clay, iron, and aluminum oxides have been lost by a process known as leaching (when water carries materials in solution down from one soil level to another). Soil composition refers to the material of which it is made.

The color of the soil is related to its composition.

Soil moisture can also affect its color. Soil Classification:
Rock material in soil consists of three main types: Clay, Silt and Sand.

The proportion of clay, silt and sand in soil depends on the soil's parent rock. soil profile:
a vertical section of soil that shows the layers of horizons
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