Nature and distribution of South African plinthic soils: Conditions for occurrence of soft and hard plinthic soils

Abstract

The relevance of using redox morphology and irreversible hardened material to classify soft and hard plinthic soil forms is often questioned as the paleoclimate of South Africa varied significantly. Since the origin of the Soil Classification System of South Africa in 1965, enough soils have been classified to test the ability of the classification system to distinguish between different entities and the relevance of the criteria applied to classify plinthic soils. Data of 203 plinthic profiles, classified by various workers, were plotted in phase diagrams and interpreted. Results indicate that the Soil Classification System of South Africa is user friendly and can be applied with success. Soft and hard plinthic soils occur in different phases of environmental conditions. Both the dominant factors of soil formation currently controlling the soil water regime and the soil properties expected to relate to the conditions of soil formation differ between the plinthic soil forms. The soils, therefore, formed under conditions similar or related to present day conditions.

Keywords:

• Mottles
• relict features
• soil classification
• soil morphology