Agricultural Science (AS)·Soil · NSSCAS 2.2
Soil colour & structure
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Why does the soil glow red-orange in the Kalahari, turn pale grey on the calcrete flats, and come up almost black under an old kraal — all in the same country? A soil's colour is a free clue about what lies inside it, and the way it crumbles in your hand tells you whether roots will thrive or struggle. In this lesson we learn to read Namibia's soil colours, find out what causes them, and discover how a careful farmer builds and guards good soil structure.
What you'll learn in this lesson
By the end you should be able to (NSSCAS Agricultural Science (AS) 2.2):
- Describe the soil colours found across Namibia — red and reddish-brown arenosols, pale grey calcisols, dark organic soils, yellow soils and dark clay vertisols
- Outline the factors that influence soil colour: organic matter content, iron oxides and their oxidation state, moisture and drainage, parent material, and minerals such as calcium carbonate
- Explain the importance of the different soil colours in relation to plant growth
- Define soil structure and explain what a ped and a pore are
- Describe the main types of soil structure: single-grain, crumb, granular, blocky, platy and prismatic or columnar
- Explain how good soil structure supports the growth of plants
- Describe how soil structure can be maintained and improved, using organic matter, avoiding compaction, minimum tillage, cover crops and correcting salinity
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