are recognised as a perch-gley group (or mottled subgroup)
in another soil order because the extent or depth of gleying is
insufficient to qualify for the Gley Soils order.
Gley Soils are more common in areas with higher rainfall,
particularly on the West Coast of the South Island, as there is
more opportunity for soils to be saturated for long periods of
time. Because of the saturated conditions and limited oxygen, Gley Soils are often marked by the presence of
water-tolerant vegetation such as Juncus species (rushes).
Traversing the lowlands in the nineteenth century
Travelling in early New Zealand was always challenging. In the nineteenth century, travellers struggled
against rugged alpine mountain lands, deep
steep-sided gorges, and swift rivers, where the prevalent cause of death was drowning (known at the time
as ‘the New Zealand death’). However, travel in the
lowlands was also challenging due to extensive areas
of saturated soil. Thomas and John Royds wrote, in
1861, of their nine-day journey from Dunedin to
Invercargill. They had a one shaft cart, with two
horses, carrying five tonnes of freight including
ploughs, tools, a stove, and other farm equipment.
They were severely tested by frequent river crossings
and boggy bushland tracks. The same journey now
takes just two and a half hours.
Similar stories were told throughout New Zealand,
whether it be on the saturated soils of Northland, Waikato, or in the heart of the Wairarapa Bush. The road
near Alfredton, in the Wairarapa, was a notorious
quagmire. In the 1880s one Alfred Shell became trapped
up to his thighs in mud and as night fell was sure he
would die before morning. However, he was fortunate
to be rescued some 20 h later. On another occasion one
man was not so lucky and died before help arrived.
Horses were known to be lost, saddle and all, into the
mud. Bullock trains were used as they coped better with
the deep, saturated, mud that served as a road.
In the north Wairarapa there was a lack of hard
metal (crushed rock) to form roads and one tactic used
was to get a good fire going on the clay surface—the
heat converted what was called ‘limonite’ (probably
goethite, a soft, common, iron oxide mineral) into
haematite which provided a harder material for the
road surface providing improvement for some time.
However, after a while the haematite would weather
and revert to goethite. Heating in a fire was also used
by Māori to convert ferrihydrite (an iron oxide ‘gel’) to
haematite to make red ochre (kokowai). To be effective the temperature had to reach at least 750 °C.
5.4 Key Soil Properties
5.4.1 Soil Composition
Gley Soils are most commonly formed in alluvial or colluvial parent materials, but parent material is not a defining
characteristic of Gley Soils. Thus Gley Soils have wide
ranging clay types that reflect the mineralogy of the parent
materials. The most common mineralogy groups are mixed,
illitic, smectitic, and kaolinitic. The one common mineralogical feature of Gley Soils is the segregation of iron and
manganese oxides, as a result of the redox processes
(Sect. 5.2). Particles in reduced parts of the soil are not
coated or stained by iron and manganese oxides. The oxides
migrate along biochemical gradients to congregate in redox
concentrations (mottles, concretions, and pans) at points
where oxygen is available within the soil.
5.4.2 Physical Properties
The physical properties of Gley Soils are wide ranging as a
result of the diverse parent materials and topographic situations in which Gley Soils form (Fig. 5.6). The common
feature of Gley Soils is the presence of high groundwater or
perched water tables and periodically saturated soil conditions. Thus the soils are described as poorly or very poorly
drained. Trafficability is limited in most soils when wet and
pugging damage by stock is a common risk. Rooting depths
of Gley Soils may be limited for many plants by oxygen
deprivation below the water table. Most crop plants will be
inhibited by high water tables, at least through winter
months. This restriction may be exacerbated by higher soil
dry bulk density and associated low macroporosity. Soil dry
bulk densities are likely to be higher in Gley Soils than in
well drained soils in similar soil materials. Gley Soils, particularly those on river flood plains and terraces, tend to be
relatively fine-textured with a moderate clay content
(Fig. 5.6). Gley Soils often form in the back swamp areas
where finer materials are carried by, and settle out from,
flood waters while coarser gravel and sand materials are
mainly deposited closer to river margins forming levees.
5.4.3 Chemical Properties
The topsoils in Gley Soils generally have moderate levels of
organic matter and some are peaty as the wet conditions
inhibit biodegradation of plant materials (Fig. 5.7,
Table 5.1). The mean cation exchange capacity in subsoils
of Gley Soils is high to very high (ranges from 26 to 56
cmol
(+) kg
−1 ) and phosphorus retention is low to medium.
78
5 Gley Soils
in another soil order because the extent or depth of gleying is
insufficient to qualify for the Gley Soils order.
Gley Soils are more common in areas with higher rainfall,
particularly on the West Coast of the South Island, as there is
more opportunity for soils to be saturated for long periods of
time. Because of the saturated conditions and limited oxygen, Gley Soils are often marked by the presence of
water-tolerant vegetation such as Juncus species (rushes).
Traversing the lowlands in the nineteenth century
Travelling in early New Zealand was always challenging. In the nineteenth century, travellers struggled
against rugged alpine mountain lands, deep
steep-sided gorges, and swift rivers, where the prevalent cause of death was drowning (known at the time
as ‘the New Zealand death’). However, travel in the
lowlands was also challenging due to extensive areas
of saturated soil. Thomas and John Royds wrote, in
1861, of their nine-day journey from Dunedin to
Invercargill. They had a one shaft cart, with two
horses, carrying five tonnes of freight including
ploughs, tools, a stove, and other farm equipment.
They were severely tested by frequent river crossings
and boggy bushland tracks. The same journey now
takes just two and a half hours.
Similar stories were told throughout New Zealand,
whether it be on the saturated soils of Northland, Waikato, or in the heart of the Wairarapa Bush. The road
near Alfredton, in the Wairarapa, was a notorious
quagmire. In the 1880s one Alfred Shell became trapped
up to his thighs in mud and as night fell was sure he
would die before morning. However, he was fortunate
to be rescued some 20 h later. On another occasion one
man was not so lucky and died before help arrived.
Horses were known to be lost, saddle and all, into the
mud. Bullock trains were used as they coped better with
the deep, saturated, mud that served as a road.
In the north Wairarapa there was a lack of hard
metal (crushed rock) to form roads and one tactic used
was to get a good fire going on the clay surface—the
heat converted what was called ‘limonite’ (probably
goethite, a soft, common, iron oxide mineral) into
haematite which provided a harder material for the
road surface providing improvement for some time.
However, after a while the haematite would weather
and revert to goethite. Heating in a fire was also used
by Māori to convert ferrihydrite (an iron oxide ‘gel’) to
haematite to make red ochre (kokowai). To be effective the temperature had to reach at least 750 °C.
5.4 Key Soil Properties
5.4.1 Soil Composition
Gley Soils are most commonly formed in alluvial or colluvial parent materials, but parent material is not a defining
characteristic of Gley Soils. Thus Gley Soils have wide
ranging clay types that reflect the mineralogy of the parent
materials. The most common mineralogy groups are mixed,
illitic, smectitic, and kaolinitic. The one common mineralogical feature of Gley Soils is the segregation of iron and
manganese oxides, as a result of the redox processes
(Sect. 5.2). Particles in reduced parts of the soil are not
coated or stained by iron and manganese oxides. The oxides
migrate along biochemical gradients to congregate in redox
concentrations (mottles, concretions, and pans) at points
where oxygen is available within the soil.
5.4.2 Physical Properties
The physical properties of Gley Soils are wide ranging as a
result of the diverse parent materials and topographic situations in which Gley Soils form (Fig. 5.6). The common
feature of Gley Soils is the presence of high groundwater or
perched water tables and periodically saturated soil conditions. Thus the soils are described as poorly or very poorly
drained. Trafficability is limited in most soils when wet and
pugging damage by stock is a common risk. Rooting depths
of Gley Soils may be limited for many plants by oxygen
deprivation below the water table. Most crop plants will be
inhibited by high water tables, at least through winter
months. This restriction may be exacerbated by higher soil
dry bulk density and associated low macroporosity. Soil dry
bulk densities are likely to be higher in Gley Soils than in
well drained soils in similar soil materials. Gley Soils, particularly those on river flood plains and terraces, tend to be
relatively fine-textured with a moderate clay content
(Fig. 5.6). Gley Soils often form in the back swamp areas
where finer materials are carried by, and settle out from,
flood waters while coarser gravel and sand materials are
mainly deposited closer to river margins forming levees.
5.4.3 Chemical Properties
The topsoils in Gley Soils generally have moderate levels of
organic matter and some are peaty as the wet conditions
inhibit biodegradation of plant materials (Fig. 5.7,
Table 5.1). The mean cation exchange capacity in subsoils
of Gley Soils is high to very high (ranges from 26 to 56
cmol
(+) kg
−1 ) and phosphorus retention is low to medium.
78
5 Gley Soils