![]() Soil types with an orthic A horizon are by far (>95%) the most common soils in South Africa which are used for grain production. The orthic A horizon is defined as one which is not classified as one of the other four topsoil horizons. Melanic A horizons are defined according to their dark colour and strong structure. Vertic A horizons (typical turf clay) are formed through inversion as a result of large quantity of 2:1 clays (>30%). A humic A horizon has undergone humification and eluviation (loss of clay and sesquioxides). The organic A is a topsoil horizon which is enriched with organic material (>10% C) and is therefore usually a noticeably darker colour than the underlying horizon. Figure 1: The Champagne soil form has an organic O as topsoil horizon and organic material accumulates in this horizon due to conditions which inhibit microbes from breaking it down. These are the organic O, humic A, vertic A, melanic A and orthic A horizon. Only five diagnostic topsoil horizons are acknowledged. The sequence of diagnostic horizons determines the soil form. In order to classify a soil, the master horizons must first be marked out, after which these master horizons are classified into diagnostic horizons. The rest of this article is based on the Taxonomic System. A few of the most common soil forms and their allied soil forms, which are used for grain production in South Africa, are discussed in this article. Combinations of the horizons give rise to the recognition of 74 soil forms in the Taxonmic System and 135 natural soil forms and 7 anthropogenic soil forms in the Natural and Anthropogenic System. The third issue namely Soil Classification: A Natural and Anthropogenic System for South Africa, was published in June 2018.Īccording to Soil Classification: A Taxonomic System for South Africa, five topsoil horizons and 25 subsoil horizons are recognised as diagnostic (may be used to classify the master horizons in a soil profile). It was followed in 1991 by Soil Classification: A Taxonomic System for South Africa, and is currently used exclusively in South Africa to classify soils. These two systems may be used to classify soils throughout the world.Īs these systems do not make provision for the full variety of South African soils, Soil Classification: A Binomial System for South Africa was published in 1977. The two best known soil classification systems in the world are the World Reference Base (WRB) and the USDA Soil Taxonomy (a system developed in the USA). In this article, the classification of South African soils will be discussed. ![]() Also, the properties thereof may be interpreted, after which the suitability of this body of soil may be evaluated for a specific land use. ![]() When a specific body of soil is classified, the characteristics thereof may be easily communicated. These characteristics are used as the basis to classify soils into related groups. With these factors and processes in action, it gives rise to a variety of chemical, physical and morphological characteristics. In the previous two articles in this series, the soil formation factors and processes were discussed.
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