Soil Morphology

Soil Morphology

Soil morphology is the visual observation of morphological features of soil i.e. soil colour, texture and structure of horizon and arrangements of these horizons in the soil profile. This can be studied in the field by the naked eye (macro morphology), with the aid of hand lens and binocular stereoscope (meso morphology), with the electron microscope (micro morphology).

Soil Profile

                                A vertical section of the soil showing different layers and extending into the C-horizon or parent material (R layer) is called soil profile.

Horizon

                                It is a layer of soil approximately parallel to the soil surface, having different properties and characteristics from adjacent layers below or above it.

Description of typical Soil Profile

                                A common sequence of horizons within a profile comprises of five master soil horizons i.e. O, A, E, B and C. Distinctions within these master horizons are designated by the subscripts to indicates subordinates distinction within the master horizons and layers e.g. Ap, Bt, etc.
Different master horizons or layers that might occur in a soil profile are described briefly in the form of a diagram.

O Horizon (organic)

                                The O horizon is comprised of organic material that forms above the mineral horizon. This result from litter derived from dead plant and animals. O horizon usually occurs in forested areas and generally absent in grassland regions.

A Horizon

                                A horizon forms at the surface or below an O layer. A horizon shows one of the following properties.
 An accumulation of humified organic matter intimately mixed with the mineral fraction results darker in color than that of the lower horizons.  Not dominated by characteristics of the E or B horizons. Have properties resulting from cultivation, pasturing, or other similar kinds of disturbance.

E horizon

                                It is a mineral horizon from which silicate clay, iron, aluminum or some combination of these have been eluviated. Sand and/or silt sized quartz or other resistant minerals remain there and become concentrated. An E horizon is generally lighter in color than A horizon and is found below the A horizon.
Eluviation: it is the movement of material out of a portion/layer of soil profile as in E horizon.

B Horizon

                                Horizon that forms below an O, E or A horizon and shows illuviation of material from above E horizon. In humid regions, B horizon shows the accumulation of Fe/Al oxides, silicates clays and humus. In arid and semiarid regions calcium carbonate and calcium sulfate and other salts may accumulate in B horizon.
Illuviation: it is the movement of material into a portion/layer of soil profile as in B horizon.

C Horizon

                In this horizon unconsolidated material is underlying the solum (A, E and B horizons). Minerals horizons are relatively unaffected by pedogenic process and lacking the properties of O, A, E or B horizons. It may be like or unlike the parent material from which solum of soil develops.
R layer (Bedrock): it is of hard bedrock not practically digable with a spade and shows no or little evidence of weathering.
Transition Horizons: these are layers of soil between two master horizons. These exhibit properties of both the master horizons e.g. AB and BA.





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