South African Soil Classification System Part 1

Summary

This video script explores the South African soil classification system, highlighting the hierarchical structure of soil forms and families. It delves into the importance of diagnostic horizons for soil identification and discusses the impact of soil properties on various land uses, including agriculture, forestry, and wildlife reserves. The practical session at Eukalinga Farm showcases different soil profiles, such as Misper, Oak Leaf, and Long Lands, examining their characteristics, challenges, and potential uses in the context of a semi-arid climate and unique geological formations.

Takeaways

• 📚 The South African soil classification system, outlined in the 1991 'blue book', categorizes soils into 73 forms and 404 families based on diagnostic horizons.
• 🌱 Soil classification at the form level requires the recognition of unique vertical sequences of diagnostic horizons, such as the melanic and pedocutanic horizons in the Bonheim soil form.
• 🏞 Soils have various uses beyond arable agriculture, including forestry, engineering, and wildlife reserves, and their properties affect these uses significantly.
• 🌡 The Eukalinga farm, where the practical takes place, has a semi-arid climate with a hot, wet summer and a warm, dry winter, influencing the types of soils found there.
• 🏔 The topography of Eukalinga consists of a lower slope and an upper plateau, with the plateau having a saucer-like shape that affects water flow and soil characteristics.
• ⏳ Time is an abstract factor in soil formation, with soil age inferred from observable properties rather than direct measurement.
• 🚫 Misper soil form, characterized by thin topsoil over echo shale, is not suitable for arable crops or forestry due to its shallow nature and the semi-arid climate.
• 🌳 Oak leaf soil form is deeper and has a reddish color indicating good drainage; it is suitable for arable crops and potentially forestry, except for the climatic constraint of the area.
• 🐀 The presence of earthworms and moles in the soil is a sign of a healthy ecosystem, with moles being particularly active in areas with high earthworm populations.
• 🌊 Long lands soil form has a gray, mottled e horizon indicating wetness close to the surface during certain times of the year, characteristic of a wet season/dry season environment.
• 🛠 The presence of iron in the soil, such as in the Long lands form, can be attributed to the weathering of nearby dolorite boulders, which contribute to the formation of plinthic material.

Q & A

What is the basis for the classification of soils in the South African soil classification system?

The classification is based on the information given in the 'South African Soil Classification' published in 1991, commonly referred to as the 'blue book'. It is a hierarchical system with two levels: the more general 'soil form' and the more specific 'soil family'.

How many soil forms and soil families are identified in the South African soil classification system?

The system divides the soils of South Africa into 73 soil forms and 404 soil families.

What are 'diagnostic horizons' in the context of soil classification?

Diagnostic horizons are unique vertical sequences of soil layers that are used to recognize and classify soil forms, as each soil form is defined based on these horizons.

What is the significance of the melanic horizon in the Bonheim soil form?

In the Bonheim soil form, the melanic horizon is significant as it overlies a pedocutanic B horizon, and this presence helps define the Bonheim soil form.

How many diagnostic topsoils and subsoil horizons or materials are defined in the South African soil classification system?

The system defines a total of five diagnostic topsoils, including the organic O horizon and 4A horizons (humic, vertic, melanic, and orthic), and 25 diagnostic subsoil horizons or materials.

What are some of the uses of soils beyond arable agriculture?

Soils are used for various purposes including forestry, engineering, and wildlife reserves, and their properties can affect these and many other uses.

What is the climate like at the University of Natal Research Farm, Eukalinga Farm?

Eukalinga Farm has a semi-arid climate with hot, wet summers and warm, dry winters. It receives about 700 millimeters of rain a year, mostly in the form of heavy thunderstorms during the summer months.

What is the role of time in soil formation?

Time is an abstract concept in soil formation that cannot be directly seen or measured. Instead, the age of soils is inferred from observable properties, and it is better to think of soils in relative terms such as being young or old.

What are the characteristics of the Misper soil form?

The Misper soil form is characterized by an extremely thin topsoil, a sharp boundary onto the underlying echo shale parent material, and its non-arable nature due to its shallow depth and susceptibility to erosion.

Why is the Oak Leaf soil form considered more suitable for arable use than the Misper soil form?

The Oak Leaf soil form is deeper, well-drained, and has a moderate level of fertility, making it suitable for deep-rooted crops. It also lacks the shrink-swell issues of the Misper soil form, making it less prone to erosion and more suitable for various uses including arable agriculture, although the semi-arid climate may still limit certain uses.

What is the significance of the red color in the Oak Leaf soil form?

The red color in the Oak Leaf soil form signifies good drainage, which is an important characteristic for soil health and usability.

What evidence of earthworm and mole activity can be observed in the field?

Evidence of earthworm activity can be seen in the form of earthworm casts, while mole activity is indicated by mole hills, especially in areas with the Oak Leaf soil form where good drainage supports their presence.

What are the characteristics of the Long Lands soil form?

The Long Lands soil form is characterized by a thin or thick topsoil over a gray mottled E horizon, which indicates wet conditions close to the surface at certain times of the year. Beneath the E horizon is soft plinthic material that hardens upon exposure.

How does the presence of iron in the Long Lands soil form affect its properties?

The presence of iron, likely from weathered dolorite, contributes to the formation of soft plinthic material. Over time, this can harden due to exposure, and the iron also contributes to the reddish mottles seen in the soil.

What is the role of lateral subsurface flow in the formation of the Long Lands soil form?

Lateral subsurface flow, driven by the horizontally bedded ekka shale, leads to the bleaching of the E horizon and the accumulation of iron closer to the shale, contributing to the formation of the plinthic material.