5. COLOUR AND COLOUR MOTTLING
5.0 Colour of soil horizons
How do you
define the colour of soil horizons?
The colour of individual horizons should be
defined when the soil is moist , as soon as
visible moisture films disappear from a moistened
sample. Specialists usually refer to the Munsell
Soil Colour Charts to define the colour of
horizons. For the purpose of this manual, a
simpler system is used, including the following
shades of colour:
Shades of colour
What may colour
In the surface soil such as the A-horizon, darker
shades usually indicate a higher content of organic matter than
lighter shades. This, however, is not always true as, in high
rainfall areas, dark soil colouring can be caused by poor drainage.
In deeper horizons such as the B-horizon, a
brown colour usually means that the soil has good natural
drainage. A black or dark grey colour usually comes from an accumulation
of organic matter. In areas of high rainfall, this may again
mean poor drainage.
A typical colour description
for a soil profile
Dark reddish brown
Dark reddish brown
5.1 Colour mottling in soil
What is colour mottling and how do you describe it?
The presence of spots or streaks of a particular
colour, usually reddish, yellowish or white, which may
exist in certain soil horizons is referred to as colour
- If there is a definite background colour, colour
mottling is described by determining and noting
the amount and colour of the mottles*, such as,
for example, reddish yellow horizon with common
yellowish red and white mottles;
- If the amount of mottles is so great that it is
not possible to see a single background colour,
define and note the various colours you see and
add the word mottled, such as, for example, red,
What does colour mottling indicate?
Colour mottling is strong whenever a soil is subject
to waterlogging, even if the soil is highly permeable.
However, colour mottling may also occur for other reasons.
If mottling occurs in a bright-coloured B-horizon, it
is not related to a drainage
If mottling occurs in any horizon with any dull colour,
usually grey, it is a sign of drainage
problems for a major part of the year, regardless of
the absence or presence of water.
Abundant pale yellow mottles coupled with a low pH
characterize actual acid
Various colours of soil and mottling as they relate to
drainage conditions are given below.
|Warm colours, browns, reds and oranges
|Pale yellowish, pale and dark greys with rusty
orange and/or grey mottling within the waterlogged horizon;
grey colours are common as well
|Drainage seasonally poor
Water-table at 25- to 120-cm depth
|Pale, dark and bluish greys, or pale brownish
yellows with rusty orange, brown or grey mottling within
|Seasonally swampy soil
Water-table at less than 25-cm depth
Colour combined with colour mottling may also be used as one
of the visual indicators of soil permeability