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Soil Colour

Soil Colour | Soil Particles | Bonding and Aggregation | Porosity | Changing Soil Structure | Soil Strength

What does soil colour indicate?
Colour is an obvious characteristic of soil. It can provide a valuable insight into the soil environment. Thus it can be very important in assessment and classification.

What are soil colours?
The most influential colours in a well drained soil are white, red, brown and black. White indicates the predominance of silica (quartz), or the presence of salts; red indicates the accumulation of iron oxide; and brown and black indicate the level and type of organic matter. A colour triangle can be used to show the names and relationships between the influential colours.

What determines soil colour?
Four main factors influence the colour of a soil:

• Mineral matter derived from the constituents of the parent material
• Organic matter
• The nature and abundance of iron
• Moisture content

For further information go to Interpreting soil colour

What does soil colour tell us?
If we understand what determines soil colour, then we can use colour to make some inferences about, history, chemistry and hydrology. For example, an obvious change in colour between horizons is a real indication of changes in soil properties which are the result of biological activity, water movement and weathering.

How do you measure soil colour?

• Soil colour should be determined on moist surfaces of freshly broken (not sliced) soil samples.
• Like any other soil property, colour must always be observed throughout soil profile, paying special attention to the differences between soil horizons. Colour characteristics such as mottle size, percentage and contrast should be observed and recorded.
• A system that uses specially printed colour charts (Munsell Soil Colour Charts) gives an international standard. It divides colour into wavelength, lightness, and colour saturation. More on this is provided at Interpreting soil colour
• Where a Munsell Chart is not available, simple names as listed in the above triangle can be used.

Practical Note: Soil Colour Colour is one of the most obvious characteristics of soil. Colour can also provide a valuable insight into the soil environment and hence is very important in assessment and classification. The most influential colours in a well drained soil are white, red, brown and black.