Answer to Question #161160 in Mechanical Engineering for James Woatsi

Question

1. Describe the various horizons of the soil profile.

2. State any five importance of the soil profile.

Answer 1

O) Organic surface layer: Plant litter layer, 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. It has a pronounced soil structure. But in some soils, clay minerals, iron, aluminum, organic compounds, and other constituents are soluble and move downwards. When this eluviation is pronounced, a lighter coloured E subsurface soil horizon is apparent at the base of the A horizon. The A horizon may also be the result of a combination of soil bioturbation and surface processes that winnow fine particles from biologically mounded topsoil. In this case, the A horizon is regarded as a "biomantle".

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 soil, where substances move down from the topsoil, this is the layer where they accumulate. The process of accumulation of clay minerals, iron, aluminum, and organic compounds, is referred to as illuviation. The B horizon has generally a soil structure.

C) Substratum: Layer of non-indurated poorly weathered or unweathered rocks. This layer may accumulate more soluble compounds like CaCO₃. Soils formed in situ from non-indurated material exhibit similarities to this C layer.

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 (as opposed to boulders) of hard rock that cannot be excavated by hand. Soils formed in situ from bedrock will exhibit strong similarities to this bedrock layer.

0 horizon-loose and partly decayed organic matter (think of decomposing leaves)

A horizon-mineral matter mixed with humus

E horizon-light colored zone of leaching (water filter through material)

B horizon-accumulation of clay from above

C horizon-partially altered parent material

under that-unweathered parent material)

Resource: https://en.wikipedia.org/wiki/Soil_horizon

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