Concept of Soil Morphology

More recently, the soil has come to be recognized as a 3 – dimensional body having length, depth as well as breadth. This has given rise to the concept of pedon.

The term pedon is used to describe the smallest 3- dimensional body of soil with lateral dimensions large enough to permit the study of the nature and arrangement of horizons and variability in other properties that are preserved in samples.

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The pedon is considered to be the smallest volume which satisfactorily represents soil. Thus it can be compared to a unit cell of a crystal but too small to appear as a mapping unit. So in general, it is normally considered a sampling unit. 

The area of the pedon ranges from 1 – 10m2 depending on the variability in the soil. Its lower limit is somewhat vague. It is taken as the limit between the soil and “not-soil” below. The lateral dimension (width) is large enough to represent the nature of any horizon.

The Soil Individual or Polypedon

Modern soil science makes use of the concept of polypedon which is the smallest distinctive division of the soil of a given area. The individuals being mapped are the polypedon or what some prefer to call soil individuals. 

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They consist of one or more similar pedons bounded on all sides by ‘not soils” or by pedons of unlike character in respect to one or more characteristics diagnostic for a soil series.

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Characteristics here refer to the nature and arrangement of horizons if horizons are present. By nature of horizons, we mean composition including mineralogy, structure, consistency, texture, moisture regime, etc. 

A polypedon has a minimum area greater than 1m2 and an unspecified maximum area. It has some characteristics such as shape, transitional margins, and natural boundaries that are not possessed by any one of its component pedons. The soil individuals or polypedons are the real objects that pedologists classify hence it is called a unit of classification.

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