determines the subsequent soil formation pathway. Later,
climate and vegetation, and the passage of time, become the
more important controls over the character of the soil that
develops from particular parent materials.
Soils will only proceed the whole way down a soil formation pathway on relatively stable sites. Erosion, soil
mixing or disturbance (pedoturbation), or the addition of
fresh sediment or tephra, will potentially impede, retard,
halt, or even reverse, soil progress along a genetic pathway.
Many, perhaps most, Raw Soils may never develop into
Recent Soils or other soils because they occur in environments with continual cycles of erosion or frequent additions
of new materials. Some soil orders may form quickly (in c.
1000–5000 years) when conditions are favourable, such as
‘young’ Podzol Soils that have formed under high rainfall on
free-draining sands dominated by Nothofagus (beech) in
Westland, or on well drained pumice (Taupo Tephra, c.
1800 years old) under podocarp-dominated forest at >500 m
altitude, and moderately high rainfall, on the Mamaku Plateau. At the same time, some Podzol Soils are likely to be
some hundreds of thousands of years old as one of the most
evolved (mature) soils in New Zealand. The most strongly
developed soils, Podzol Soils, Ultic Soils, Granular Soils,
and Oxidic Soils, have each passed through earlier phases at
an intermediate stage of their evolution (Fig. 18.2). Similarly, the (Weathered) Aged-argillic Semiarid Soils, which
may be c. 350,000 years old, represent a soil developed on
the oldest (most elevated) of four terrace surfaces in Central
Otago. It is therefore inferred to have been through each of
the preceding stages of soil development recognised on the
three successively younger terrace (and fan) land surfaces
(Chap. 15).
Undisturbed Organic Soils are likely to develop from
Fibric, through Mesic, to Humic groups, with time, as the
organic materials progressively decompose. If no fresh
organic material is added, and if the water table drops or
becomes more oxygenated, the organic content will
decompose to a point that the soil eventually becomes
mineral dominated and will then develop down a mineral
pathway.
The pathways included in Fig. 18.2 represent mainly
those likely to have occurred over extensive areas. For
clarity, minor pathways or interlinkages have been omitted,
but we have included two exceptions: (i) allophanic material
may be formed from non-tephric deposits by the strong
leaching of unconsolidated quartzo-feldspathic and micaceous materials, and hence lead to allophanic groups such as
Allophanic Brown Soils; and (ii) Ultic Soils may be formed
in mafic or tephra-derived parent materials given long time
periods in a warm moist climate.
Although the major genetic pathways of soil formation
(Fig. 18.2) are essentially global, some features reflect the
distinctive parent materials and climatic conditions of New
Zealand, in turn, related strongly to the active tectonic setting in an oceanic, mid-latitude location. For example,
Andisols (Allophanic Soils, Pumice Soils, and Tephric
Recent Soils combined) cover *13% of New Zealand’s
land area (the third most common Soil Taxonomy order in
New Zealand), yet globally Andisols represent only 0.84%
of the land area, 12th in the global ranking by area.
The distinctive elements of New Zealand soil-forming
processes reflect some combination of low calcium carbonate
(lime) content, lack of surface casting native soil fauna, generally low incidence of fire in our forests, and a nutrient
conservative flora that cannot drive the soil-plant system to its
potential. Thus, rapid acidification in lime-free parent materials has occurred under nutrient conservative native forest
vegetation with little bioturbation of surface horizons, apart
from tree throw. The accumulation of acid organic matter has
led to less movement (illuviation) of clay down the profile, and
more brunification and (especially) podzolisation, than would
be expected in similar environments internationally.
18.4 Soil and Land Evaluation in New
Zealand
18.4.1 Introduction
If we could breed soils what would a champion soil look
like? This was a question posed by Eddie Cutler of Lincoln
University in the 1960s. His answer would have been conditioned by the prevailing productive pastoral agriculture of
the landscape in which he worked. His ideal soil would have
had an earthy (crumb) structure (like breadcrumbs), a
fine-sandy loam texture, and been well drained. More than
50 years later, however, we would have to answer by saying
‘it depends’. To meet the needs of different plants, land
management, and environmental requirements, a range of
‘ideal’ soils that is fit for a specific purpose are recognised.
For example, a champion soil to support pasture for dairy
grazing requires a high capacity to store water, and resistance to bypass flow so that water stress that would impede
pasture growth is ideally avoided, and rapid leaching of
nutrients or contaminants to groundwater is minimised. In
the same locality, a soil for the production of medal-winning
wines may need the opposite capability, with low water
storage capacity required to induce drought stress and help
the management of sugars and alcohol.
Although we cannot breed soils, they can be modified in
ways that may persist for a long time. Modifications include
drainage to remove excess water and liming to make soils
less acidic and more hospitable to food production. A more
severe example is deep ripping or ‘flipping’, where the entire
soil profile is inverted, to improve drainage or water holding
capacity (Chap. 3, Anthropic Soils).
296
18 Conclusion: Global Context, Formation Pathways …
climate and vegetation, and the passage of time, become the
more important controls over the character of the soil that
develops from particular parent materials.
Soils will only proceed the whole way down a soil formation pathway on relatively stable sites. Erosion, soil
mixing or disturbance (pedoturbation), or the addition of
fresh sediment or tephra, will potentially impede, retard,
halt, or even reverse, soil progress along a genetic pathway.
Many, perhaps most, Raw Soils may never develop into
Recent Soils or other soils because they occur in environments with continual cycles of erosion or frequent additions
of new materials. Some soil orders may form quickly (in c.
1000–5000 years) when conditions are favourable, such as
‘young’ Podzol Soils that have formed under high rainfall on
free-draining sands dominated by Nothofagus (beech) in
Westland, or on well drained pumice (Taupo Tephra, c.
1800 years old) under podocarp-dominated forest at >500 m
altitude, and moderately high rainfall, on the Mamaku Plateau. At the same time, some Podzol Soils are likely to be
some hundreds of thousands of years old as one of the most
evolved (mature) soils in New Zealand. The most strongly
developed soils, Podzol Soils, Ultic Soils, Granular Soils,
and Oxidic Soils, have each passed through earlier phases at
an intermediate stage of their evolution (Fig. 18.2). Similarly, the (Weathered) Aged-argillic Semiarid Soils, which
may be c. 350,000 years old, represent a soil developed on
the oldest (most elevated) of four terrace surfaces in Central
Otago. It is therefore inferred to have been through each of
the preceding stages of soil development recognised on the
three successively younger terrace (and fan) land surfaces
(Chap. 15).
Undisturbed Organic Soils are likely to develop from
Fibric, through Mesic, to Humic groups, with time, as the
organic materials progressively decompose. If no fresh
organic material is added, and if the water table drops or
becomes more oxygenated, the organic content will
decompose to a point that the soil eventually becomes
mineral dominated and will then develop down a mineral
pathway.
The pathways included in Fig. 18.2 represent mainly
those likely to have occurred over extensive areas. For
clarity, minor pathways or interlinkages have been omitted,
but we have included two exceptions: (i) allophanic material
may be formed from non-tephric deposits by the strong
leaching of unconsolidated quartzo-feldspathic and micaceous materials, and hence lead to allophanic groups such as
Allophanic Brown Soils; and (ii) Ultic Soils may be formed
in mafic or tephra-derived parent materials given long time
periods in a warm moist climate.
Although the major genetic pathways of soil formation
(Fig. 18.2) are essentially global, some features reflect the
distinctive parent materials and climatic conditions of New
Zealand, in turn, related strongly to the active tectonic setting in an oceanic, mid-latitude location. For example,
Andisols (Allophanic Soils, Pumice Soils, and Tephric
Recent Soils combined) cover *13% of New Zealand’s
land area (the third most common Soil Taxonomy order in
New Zealand), yet globally Andisols represent only 0.84%
of the land area, 12th in the global ranking by area.
The distinctive elements of New Zealand soil-forming
processes reflect some combination of low calcium carbonate
(lime) content, lack of surface casting native soil fauna, generally low incidence of fire in our forests, and a nutrient
conservative flora that cannot drive the soil-plant system to its
potential. Thus, rapid acidification in lime-free parent materials has occurred under nutrient conservative native forest
vegetation with little bioturbation of surface horizons, apart
from tree throw. The accumulation of acid organic matter has
led to less movement (illuviation) of clay down the profile, and
more brunification and (especially) podzolisation, than would
be expected in similar environments internationally.
18.4 Soil and Land Evaluation in New
Zealand
18.4.1 Introduction
If we could breed soils what would a champion soil look
like? This was a question posed by Eddie Cutler of Lincoln
University in the 1960s. His answer would have been conditioned by the prevailing productive pastoral agriculture of
the landscape in which he worked. His ideal soil would have
had an earthy (crumb) structure (like breadcrumbs), a
fine-sandy loam texture, and been well drained. More than
50 years later, however, we would have to answer by saying
‘it depends’. To meet the needs of different plants, land
management, and environmental requirements, a range of
‘ideal’ soils that is fit for a specific purpose are recognised.
For example, a champion soil to support pasture for dairy
grazing requires a high capacity to store water, and resistance to bypass flow so that water stress that would impede
pasture growth is ideally avoided, and rapid leaching of
nutrients or contaminants to groundwater is minimised. In
the same locality, a soil for the production of medal-winning
wines may need the opposite capability, with low water
storage capacity required to induce drought stress and help
the management of sugars and alcohol.
Although we cannot breed soils, they can be modified in
ways that may persist for a long time. Modifications include
drainage to remove excess water and liming to make soils
less acidic and more hospitable to food production. A more
severe example is deep ripping or ‘flipping’, where the entire
soil profile is inverted, to improve drainage or water holding
capacity (Chap. 3, Anthropic Soils).
296
18 Conclusion: Global Context, Formation Pathways …