higher, and more evenly distributed through the year, Brown
Soils occur.
Podzol Soils form where there is a high rainfall, along
with good drainage, to facilitate leaching, and particular
plants that provide a source of acidic organic material to the
soil. Rimu (Dacrydium cupressinum), kauri (Agathis australis), and beech (Nothofagus sp.) trees are all common
sources of acid litter associated with Podzol Soils in New
Zealand.
Collectively, the Semiarid Soils, Pallic Soils, Brown
Soils, and Podzol Soils extend over 73% of New Zealand
(Figs. 1.12 and 1.13).
d. Soils dominated by wetness—Organic Soils and Gley
Soils
In topographically low-lying areas, or in soils with subsoil
impediments to drainage, water tends to accumulate on or
near the soil surface. Where plants grow in a saturated
environment, dead plant material tends to accumulate in the
water and, rather than biodegrading, forms peat. Soils with
thick peat, described as ‘organic soil materials’, are classified
as Organic Soils, as are soils under forest with thick
( 40 cm) surface layers of organic matter, including
decomposed leaf litter. Climate and in some cases altitude
play roles additional to that of topography for maintaining
peatlands because the number of rain-days per year (not just
amount of rain) can become critical to the ongoing development of peat and thus Organic Soils.
The Gley Soils are saturated with water for at least part of
the year, so that all the oxygen present is used by microbes,
resulting in anaerobic conditions. Saturated conditions can
strongly affect the growth and types of plants by limiting the
availability of oxygen to roots. The duration and depth to
wetness is indicated by accumulation of organic matter and
soil colours. Dominant pale grey or blueish colours indicate
prolonged wetness (reducing conditions), and rust-coloured
mottles, or concretions, in a paler matrix indicate intermittent
wetness (redox conditions). Gley Soils form in low-lying
areas with high water tables, or where water saturates the soil
surface for extended periods because of low permeability or
impeded drainage.
Large areas of Gley and Organic Soils are now used for
productive agriculture or horticulture but the wetness indicators persist as evidence of the extent of wetlands prior to
farm development and drainage.
e. Soils dominated by particular geological materials—
Pumice Soils, Allophanic Soils, and Melanic Soils
In the Pumice Soils, Allophanic Soils, and Melanic Soils the
parent material has a strong influence on the nature and
development of the resulting soil. Through central North
Island and across Taranaki, the influence of tephra (unconsolidated, fragmental, explosively erupted, pyroclastic
material) dominates the soil properties. In a large area centred on Lake Taupo are soils, called Pumice Soils, formed
mainly in glassy, pumice-dominated tephra (vitric materials)
erupted from the Taupo volcano about 1800 years ago.
Beyond the Pumice Soils, reaching into the Bay of Plenty,
King Country, parts of the Waikato, and across to Taranaki,
are Allophanic Soils that have formed mainly in finer textured, multiple tephra-fall deposits. Where limestone dominates the soil parent material, Melanic Soils occur which
have distinct, deep, dark blackish, topsoils over weathering
rock and relatively high pH. Melanic Soils also form on
dark-coloured basic or mafic (magnesium- and iron-rich)
rocks (such as basalt) or ultramafic rocks (such as dunite).
f. Ancient soils—Ultic Soils, Granular Soils, and Oxidic
Soils
Among the rolling land, hills, and terraces, from Northland
to the northern Waikato, extensive areas have generally
escaped erosion or significant deposition for more than about
50,000 years. Small areas of stable land surfaces also occur
in the Wellington, Marlborough, Nelson, Otago, and
Southland regions. The comparative stability has enabled
soil development to proceed to more advanced weathering
and leaching than in other parts of New Zealand, resulting in
soils with high clay contents, acidic pHs, and low natural
soil fertility.
On some older basalt lava flows and especially on older
tephra deposits, particularly in the South Auckland and
northern Waikato region, Granular Soils are formed. These
tend to have clay-rich subsoils, well-developed pedality, and
can be very productive. On the more silicic parent materials,
such as greywacke, Ultic Soils form with yellow, sticky
clays in subsoils, high acidity, and low soil fertility. Small
areas of Oxidic Soils, similar to soils of tropical regions,
form north of Auckland on sites that have been stable for
long periods with a warm wet climate but more iron-rich
parent materials than the sedimentary rocks that weather to
form the Ultic Soils. Upper parts of Oxidic Soils tend to be
more friable and less sticky than Granular or Ultic Soils.
1.4.3 Key to New Zealand Soil Orders
Follow the key in Fig. 1.14 to determine the soil order(s)
that occur at any site of interest. Once a soil order is identified the appropriate chapter should be consulted for more
detailed information. Correlations with international soil
classifications (Soil Taxonomy and World Reference Base)
1.4 New Zealand Soil Classification
17
Soils occur.
Podzol Soils form where there is a high rainfall, along
with good drainage, to facilitate leaching, and particular
plants that provide a source of acidic organic material to the
soil. Rimu (Dacrydium cupressinum), kauri (Agathis australis), and beech (Nothofagus sp.) trees are all common
sources of acid litter associated with Podzol Soils in New
Zealand.
Collectively, the Semiarid Soils, Pallic Soils, Brown
Soils, and Podzol Soils extend over 73% of New Zealand
(Figs. 1.12 and 1.13).
d. Soils dominated by wetness—Organic Soils and Gley
Soils
In topographically low-lying areas, or in soils with subsoil
impediments to drainage, water tends to accumulate on or
near the soil surface. Where plants grow in a saturated
environment, dead plant material tends to accumulate in the
water and, rather than biodegrading, forms peat. Soils with
thick peat, described as ‘organic soil materials’, are classified
as Organic Soils, as are soils under forest with thick
( 40 cm) surface layers of organic matter, including
decomposed leaf litter. Climate and in some cases altitude
play roles additional to that of topography for maintaining
peatlands because the number of rain-days per year (not just
amount of rain) can become critical to the ongoing development of peat and thus Organic Soils.
The Gley Soils are saturated with water for at least part of
the year, so that all the oxygen present is used by microbes,
resulting in anaerobic conditions. Saturated conditions can
strongly affect the growth and types of plants by limiting the
availability of oxygen to roots. The duration and depth to
wetness is indicated by accumulation of organic matter and
soil colours. Dominant pale grey or blueish colours indicate
prolonged wetness (reducing conditions), and rust-coloured
mottles, or concretions, in a paler matrix indicate intermittent
wetness (redox conditions). Gley Soils form in low-lying
areas with high water tables, or where water saturates the soil
surface for extended periods because of low permeability or
impeded drainage.
Large areas of Gley and Organic Soils are now used for
productive agriculture or horticulture but the wetness indicators persist as evidence of the extent of wetlands prior to
farm development and drainage.
e. Soils dominated by particular geological materials—
Pumice Soils, Allophanic Soils, and Melanic Soils
In the Pumice Soils, Allophanic Soils, and Melanic Soils the
parent material has a strong influence on the nature and
development of the resulting soil. Through central North
Island and across Taranaki, the influence of tephra (unconsolidated, fragmental, explosively erupted, pyroclastic
material) dominates the soil properties. In a large area centred on Lake Taupo are soils, called Pumice Soils, formed
mainly in glassy, pumice-dominated tephra (vitric materials)
erupted from the Taupo volcano about 1800 years ago.
Beyond the Pumice Soils, reaching into the Bay of Plenty,
King Country, parts of the Waikato, and across to Taranaki,
are Allophanic Soils that have formed mainly in finer textured, multiple tephra-fall deposits. Where limestone dominates the soil parent material, Melanic Soils occur which
have distinct, deep, dark blackish, topsoils over weathering
rock and relatively high pH. Melanic Soils also form on
dark-coloured basic or mafic (magnesium- and iron-rich)
rocks (such as basalt) or ultramafic rocks (such as dunite).
f. Ancient soils—Ultic Soils, Granular Soils, and Oxidic
Soils
Among the rolling land, hills, and terraces, from Northland
to the northern Waikato, extensive areas have generally
escaped erosion or significant deposition for more than about
50,000 years. Small areas of stable land surfaces also occur
in the Wellington, Marlborough, Nelson, Otago, and
Southland regions. The comparative stability has enabled
soil development to proceed to more advanced weathering
and leaching than in other parts of New Zealand, resulting in
soils with high clay contents, acidic pHs, and low natural
soil fertility.
On some older basalt lava flows and especially on older
tephra deposits, particularly in the South Auckland and
northern Waikato region, Granular Soils are formed. These
tend to have clay-rich subsoils, well-developed pedality, and
can be very productive. On the more silicic parent materials,
such as greywacke, Ultic Soils form with yellow, sticky
clays in subsoils, high acidity, and low soil fertility. Small
areas of Oxidic Soils, similar to soils of tropical regions,
form north of Auckland on sites that have been stable for
long periods with a warm wet climate but more iron-rich
parent materials than the sedimentary rocks that weather to
form the Ultic Soils. Upper parts of Oxidic Soils tend to be
more friable and less sticky than Granular or Ultic Soils.
1.4.3 Key to New Zealand Soil Orders
Follow the key in Fig. 1.14 to determine the soil order(s)
that occur at any site of interest. Once a soil order is identified the appropriate chapter should be consulted for more
detailed information. Correlations with international soil
classifications (Soil Taxonomy and World Reference Base)
1.4 New Zealand Soil Classification
17