5
Gley Soils
In places where water lays around
sodden soggy Gley Soils are found
with subsoil colours of grey or blue
Gley Soils are deficient in O-2.
Abstract
Gley Soils form where soils are saturated for long periods
due to high or perched water tables, or slow drainage.
Gley Soils occur throughout New Zealand but are more
common in areas of high rainfall such as the West Coast
of the South Island. Distinctive pale blue-grey colours in
Gley Soils indicate a lack of oxygen and associated
reducing conditions. When water saturates the soil,
microbes use up the available oxygen leading to anaerobic (or reducing) conditions where the iron in
rust-coloured iron oxides (containing Fe
3+ ) is reduced to
a colourless, soluble form (containing Fe
2+ ). Manganese
oxides are similarly reduced from black or brown
compounds (containing Mn
4+ ) to a pale, soluble form
(containing Mn
2+ ). The soluble, reduced cations may
migrate to places where oxygen is available, such as
along root channels or at profile texture changes. There
they may be oxidised back to Fe
3+ forming rust-coloured
(or Mn
4+ giving brown/black) mottles, concretions, or
iron pans. Many Gley Soils occur on fertile, flat, flood
plains, and terraces. Where drainage is installed they can
be highly productive for pastoral and cropping land uses.
Careful management is needed to ensure drains are
maintained and to prevent pugging and compaction
during wet periods.
5.1 Important Features of Gley Soils
5.1.1 Concept and Key Features of the Soil
Order
Gley Soils form in areas where the soil is saturated as a result
of periodic or permanent ground- or perched-water tables.
Gley Soils occur in predominantly mineral parent materials
as distinct from Organic Soils that form from the accumulation of plant material in wet conditions. In an undrained
state, Gley Soils are often low in oxygen (anaerobic), which
limits the oxygen available to plant roots, resulting in vegetation that is tolerant of wet conditions. Anaerobic (oxygen
depleted) conditions are indicated by pale blue-grey soil
colours in areas of the profile where the soil remains saturated and soil minerals are in chemically reduced forms.
Where oxygen is periodically available, for example, along
root channels or in areas where there is seasonal wetting and
drying, areas of oxidised minerals will accumulate forming
rust-coloured or orange mottles and/or small black to brown
spots or lumps (concretions or nodules, Fig. 5.1).
Large areas of Gley Soils have been artificially drained to
form productive agricultural land. When a Gley Soil has
been drained, if the mainly grey colours remain, it is still
classified as a Gley Soil.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_5
73
Gley Soils
In places where water lays around
sodden soggy Gley Soils are found
with subsoil colours of grey or blue
Gley Soils are deficient in O-2.
Abstract
Gley Soils form where soils are saturated for long periods
due to high or perched water tables, or slow drainage.
Gley Soils occur throughout New Zealand but are more
common in areas of high rainfall such as the West Coast
of the South Island. Distinctive pale blue-grey colours in
Gley Soils indicate a lack of oxygen and associated
reducing conditions. When water saturates the soil,
microbes use up the available oxygen leading to anaerobic (or reducing) conditions where the iron in
rust-coloured iron oxides (containing Fe
3+ ) is reduced to
a colourless, soluble form (containing Fe
2+ ). Manganese
oxides are similarly reduced from black or brown
compounds (containing Mn
4+ ) to a pale, soluble form
(containing Mn
2+ ). The soluble, reduced cations may
migrate to places where oxygen is available, such as
along root channels or at profile texture changes. There
they may be oxidised back to Fe
3+ forming rust-coloured
(or Mn
4+ giving brown/black) mottles, concretions, or
iron pans. Many Gley Soils occur on fertile, flat, flood
plains, and terraces. Where drainage is installed they can
be highly productive for pastoral and cropping land uses.
Careful management is needed to ensure drains are
maintained and to prevent pugging and compaction
during wet periods.
5.1 Important Features of Gley Soils
5.1.1 Concept and Key Features of the Soil
Order
Gley Soils form in areas where the soil is saturated as a result
of periodic or permanent ground- or perched-water tables.
Gley Soils occur in predominantly mineral parent materials
as distinct from Organic Soils that form from the accumulation of plant material in wet conditions. In an undrained
state, Gley Soils are often low in oxygen (anaerobic), which
limits the oxygen available to plant roots, resulting in vegetation that is tolerant of wet conditions. Anaerobic (oxygen
depleted) conditions are indicated by pale blue-grey soil
colours in areas of the profile where the soil remains saturated and soil minerals are in chemically reduced forms.
Where oxygen is periodically available, for example, along
root channels or in areas where there is seasonal wetting and
drying, areas of oxidised minerals will accumulate forming
rust-coloured or orange mottles and/or small black to brown
spots or lumps (concretions or nodules, Fig. 5.1).
Large areas of Gley Soils have been artificially drained to
form productive agricultural land. When a Gley Soil has
been drained, if the mainly grey colours remain, it is still
classified as a Gley Soil.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_5
73