SOIL COLOUR

The colour of the soil varies widely. It is an easily observable characteristic and is an important criterion in the description and classification of soils.

Colour of soil is inherited from its parent rock material (termed as lithochromic) for example red soils developed from red sandstone.

The soil colour is best determined by the comparison with the Munsell colour.

Soil colour rotation is divided into three parts:

Hue:

It denotes the dominant spectral colour (red, yellow, blue and green)

Value:

It denotes the lightness or darkness of a colour (the amount of reflected light)

Chroma:

It represents the purity of the colour (strength of the colour) For example, the numerical notation 2.5YR 5/6 suggests a hue of 2.5 YR, value of 5 and chroma of 6.The equivalent or parallel soil colour name for this Munsell notation is red.

Soil colour and composition

(a) Black and dark grey colour: The variations from black to dark grey colour of soil are mainly due to organic matter.

(b) Brown colour: This is the most common soil colour and is due to a mixture of the organic matter and iron oxides.

(c) Red-yellow colour: Red colour is associated with unhydrated ferric oxides, whereas yellow colour indicates some degree of hydration.

(d) White colour: Silica and lime generally impart white colour.

(e) Bluish and greenish colour: Some of the bluish and greenish colours are due to the presence of ferrous compounds. This reducing condition occurs in ill drained soil.

(f) Mottling colour: Colour variation or mottling in soils indicates alternating oxidizing and reducing conditions due to a fluctuating water table.