formal New Zealand soil horizon names, definitions, and
further details, are included in the New Zealand Soil
Description Handbook.
1.3.3 Key Soil Properties
a. Colour
The most obvious property of a soil is its colour. While
most soils appear as shades of brown, the colour of a soil
can reveal a great deal about the soil’s properties and origins. In order to distinguish the various shades and tones of
soil colour, scientists use specialised colour books that
define the many hues (e.g. red, blue, orange), values (how
pale or dark a colour is), and chromas (the range from grey
to bright saturated colour) (Fig. 1.8). The darkness of a
topsoil (A-horizon) provides clues as to the amount of organic matter that may be in the soil. Topsoil colour may
also provide clues about the history of the site. For instance,
soils formed under bracken fern (Pteridium aquilinum) have
a dark black colour, whereas those formed under manuka
(Leptospermum scoparium) tend to have brown topsoil.
Very pale, blueish grey colours are usually indicative of
anaerobic soils that form in saturated conditions. Pale
coloured soils with bright brown or orange spots (called
mottles) or black to reddish precipitates (called concretions)
often indicate a soil with a periodically high water table
(i.e. fluctuating conditions of oxidation and reduction,
Chap. 5).
b. Soil texture
Soil texture describes the relative proportions of sand, silt,
and clay in a soil sample. The soil particle size classes used
by the New Zealand soil science community are described in
Table 1.1. The combinations of different particle sizes
determine the soil texture (Fig. 1.9). The ‘best’ soils for
supporting plant growth are generally loams which contain a
reasonably even mixture of sand, silt, and clay so that they
are able to hold and release nutrients and also store water
while remaining well drained.
c. Soil structure (pedality)
Soil materials often cluster together to form aggregates (also
sometimes called ‘peds’, Fig. 1.10). The shape or pattern of
aggregates, and the pore spaces between them, is referred to
as soil structure or ‘pedality’. The shape, size, and strength
of soil aggregates strongly influence the soil’s physical
properties. Large, closely fitting aggregates, such as prismatic and block structures, can limit the passage of water
and plant roots through a soil. Aggregates that are readily
broken up form friable soils in which it is easy to establish a
Fig. 1.7 Names and typical
arrangement of master mineral
soil horizons. Many soils will
differ from this generalised
scheme and the New Zealand Soil
Description Handbook should be
consulted for detailed information
on all soil horizon, sub-horizon,
prefix, and suffix names and
notations
1.3 The Soil Profile and Key Soil Properties
11
further details, are included in the New Zealand Soil
Description Handbook.
1.3.3 Key Soil Properties
a. Colour
The most obvious property of a soil is its colour. While
most soils appear as shades of brown, the colour of a soil
can reveal a great deal about the soil’s properties and origins. In order to distinguish the various shades and tones of
soil colour, scientists use specialised colour books that
define the many hues (e.g. red, blue, orange), values (how
pale or dark a colour is), and chromas (the range from grey
to bright saturated colour) (Fig. 1.8). The darkness of a
topsoil (A-horizon) provides clues as to the amount of organic matter that may be in the soil. Topsoil colour may
also provide clues about the history of the site. For instance,
soils formed under bracken fern (Pteridium aquilinum) have
a dark black colour, whereas those formed under manuka
(Leptospermum scoparium) tend to have brown topsoil.
Very pale, blueish grey colours are usually indicative of
anaerobic soils that form in saturated conditions. Pale
coloured soils with bright brown or orange spots (called
mottles) or black to reddish precipitates (called concretions)
often indicate a soil with a periodically high water table
(i.e. fluctuating conditions of oxidation and reduction,
Chap. 5).
b. Soil texture
Soil texture describes the relative proportions of sand, silt,
and clay in a soil sample. The soil particle size classes used
by the New Zealand soil science community are described in
Table 1.1. The combinations of different particle sizes
determine the soil texture (Fig. 1.9). The ‘best’ soils for
supporting plant growth are generally loams which contain a
reasonably even mixture of sand, silt, and clay so that they
are able to hold and release nutrients and also store water
while remaining well drained.
c. Soil structure (pedality)
Soil materials often cluster together to form aggregates (also
sometimes called ‘peds’, Fig. 1.10). The shape or pattern of
aggregates, and the pore spaces between them, is referred to
as soil structure or ‘pedality’. The shape, size, and strength
of soil aggregates strongly influence the soil’s physical
properties. Large, closely fitting aggregates, such as prismatic and block structures, can limit the passage of water
and plant roots through a soil. Aggregates that are readily
broken up form friable soils in which it is easy to establish a
Fig. 1.7 Names and typical
arrangement of master mineral
soil horizons. Many soils will
differ from this generalised
scheme and the New Zealand Soil
Description Handbook should be
consulted for detailed information
on all soil horizon, sub-horizon,
prefix, and suffix names and
notations
1.3 The Soil Profile and Key Soil Properties
11