are included in Appendix B, with details for each New
Zealand Soil Order in the relevant chapter.
1.5 Soils in the Landscape
An understanding of the relationship between various
aspects of the landscape and the soils that form is a key skill
of pedologists (scientists who study the soil within the
landscape). Traditionally, as a pedologist worked across the
landscape observing the subtle variations within the soil and
relating them to the soil-forming factors that influence those
differences s/he developed a mental predictive ‘model’ of the
soil-landscape relationships that could then be used to predict the properties of soils on sites not yet investigated. Often
air photographs were used to give a clear overview of the
topography and as a basis for delineating the distribution of
soils based on an understanding of the soil-landscape relationships. Modern tools such as GIS allow systematic
development and recording of predictive models.
While it is usually only practical to describe individual soil
profiles the soil forms a continuum across the landscape. In
some places quite different soils gradually merge from one to
the other, with a range of ‘intergrades’ between them. In other
places there may be distinct boundaries between soils with
contrasting properties that relate to landscape units or landforms such as an alluvial terrace versus an adjacent hillslope.
Across landscapes and regions, geological, topographic,
climate, and vegetation differences can be observed which
provide clues to the underlying soil. For example, consider a
transect across the lower half of the North Island from
Foxton Beach (west coast) through Shannon and Eketahuna
to Castle Point (east coast). Raw Soils occur on the coastal
sand dunes of the west coast. Further inland Recent Soils are
formed on the older, vegetated, sand dunes and the flood
plains of the Manawatu River. In low-lying wetland areas,
where flax swamps used to hold sway, Organic Soils occur
that, following drainage and fertiliser addition, are often
favoured nowadays for potato growing. Towards Shannon
above the terrace scarp from the current river flood plain is
an older, uplifted, terrace surface which was coated in loess
(wind-blown dust) during the Last Glaciation. The summer
drought and fine silt-rich parent materials mean a Pallic Soil
will predominate. In the foothills of the Tararua Ranges, as
altitude and rainfall increase, Brown Soils form. High in the
Tararua Ranges in the cloud forest, where beech and rimu
trees grow, pockets of Podzol Soils form within a mosaic of
Brown Soils and Recent and Raw Soils near the mountain
tops in areas that have been subject to erosion. Down the
other side of the range, the mountains give way to the high
rainfall and green grass of sheep and dairy farms on the
rolling hills (Brown Soils) and river flats (Recent Soils) near
Eketahuna. Further on, towards Castle Point on the east
coast, the rainfall rapidly drops away and Pallic Soils
dominate.
Soil maps seek to capture the distribution and variability
of soils across a landscape in two dimensions. The detail that
can be included on a map depends on the scale of the
map. With the increasing move to digital soil mapping, and
the ease of ‘zooming in’ on a map to a large scale (called the
visualisation scale), caution needs to be exercised in interpreting such maps as it is important to know the scale, and
thus the level of detail, of the original data that were used to
compile the map.
In order to capture the variability of soils in the landscape, soil maps may include soil associations and soil
complexes. A soil association can be mapped where two or
more soils form a predictable pattern in the landscape but
occur at a scale too fine to show at the map scale being used.
Soil complexes can be mapped where two or more soils
occur within a map unit but the pattern is not readily predictable using microtopography or other visual clues.
Digital soil mapping may be used to make soil surveys by
replicating the decision-making process of conventional soil
survey using the field observations made by a pedologist and
relating them to the soil-forming factors (defined in a GIS)
that control soil distribution. For example, attributes of the
climate, landform, vegetation, geology, and soil age. The
relationships can be expressed as a statistical soil-landscape
model to predict soils at locations that have not been sampled. Gradual soil changes across the landscape and measures of map confidence, as well as links to more detailed
information, may be included with digital soil maps. A digital soil map of New Zealand (S-map), developed by Manaaki Whenua – Landcare Research, is accessible online at
https://smap.landcareresearch.co.nz/.
18
1 Introduction
Zealand Soil Order in the relevant chapter.
1.5 Soils in the Landscape
An understanding of the relationship between various
aspects of the landscape and the soils that form is a key skill
of pedologists (scientists who study the soil within the
landscape). Traditionally, as a pedologist worked across the
landscape observing the subtle variations within the soil and
relating them to the soil-forming factors that influence those
differences s/he developed a mental predictive ‘model’ of the
soil-landscape relationships that could then be used to predict the properties of soils on sites not yet investigated. Often
air photographs were used to give a clear overview of the
topography and as a basis for delineating the distribution of
soils based on an understanding of the soil-landscape relationships. Modern tools such as GIS allow systematic
development and recording of predictive models.
While it is usually only practical to describe individual soil
profiles the soil forms a continuum across the landscape. In
some places quite different soils gradually merge from one to
the other, with a range of ‘intergrades’ between them. In other
places there may be distinct boundaries between soils with
contrasting properties that relate to landscape units or landforms such as an alluvial terrace versus an adjacent hillslope.
Across landscapes and regions, geological, topographic,
climate, and vegetation differences can be observed which
provide clues to the underlying soil. For example, consider a
transect across the lower half of the North Island from
Foxton Beach (west coast) through Shannon and Eketahuna
to Castle Point (east coast). Raw Soils occur on the coastal
sand dunes of the west coast. Further inland Recent Soils are
formed on the older, vegetated, sand dunes and the flood
plains of the Manawatu River. In low-lying wetland areas,
where flax swamps used to hold sway, Organic Soils occur
that, following drainage and fertiliser addition, are often
favoured nowadays for potato growing. Towards Shannon
above the terrace scarp from the current river flood plain is
an older, uplifted, terrace surface which was coated in loess
(wind-blown dust) during the Last Glaciation. The summer
drought and fine silt-rich parent materials mean a Pallic Soil
will predominate. In the foothills of the Tararua Ranges, as
altitude and rainfall increase, Brown Soils form. High in the
Tararua Ranges in the cloud forest, where beech and rimu
trees grow, pockets of Podzol Soils form within a mosaic of
Brown Soils and Recent and Raw Soils near the mountain
tops in areas that have been subject to erosion. Down the
other side of the range, the mountains give way to the high
rainfall and green grass of sheep and dairy farms on the
rolling hills (Brown Soils) and river flats (Recent Soils) near
Eketahuna. Further on, towards Castle Point on the east
coast, the rainfall rapidly drops away and Pallic Soils
dominate.
Soil maps seek to capture the distribution and variability
of soils across a landscape in two dimensions. The detail that
can be included on a map depends on the scale of the
map. With the increasing move to digital soil mapping, and
the ease of ‘zooming in’ on a map to a large scale (called the
visualisation scale), caution needs to be exercised in interpreting such maps as it is important to know the scale, and
thus the level of detail, of the original data that were used to
compile the map.
In order to capture the variability of soils in the landscape, soil maps may include soil associations and soil
complexes. A soil association can be mapped where two or
more soils form a predictable pattern in the landscape but
occur at a scale too fine to show at the map scale being used.
Soil complexes can be mapped where two or more soils
occur within a map unit but the pattern is not readily predictable using microtopography or other visual clues.
Digital soil mapping may be used to make soil surveys by
replicating the decision-making process of conventional soil
survey using the field observations made by a pedologist and
relating them to the soil-forming factors (defined in a GIS)
that control soil distribution. For example, attributes of the
climate, landform, vegetation, geology, and soil age. The
relationships can be expressed as a statistical soil-landscape
model to predict soils at locations that have not been sampled. Gradual soil changes across the landscape and measures of map confidence, as well as links to more detailed
information, may be included with digital soil maps. A digital soil map of New Zealand (S-map), developed by Manaaki Whenua – Landcare Research, is accessible online at
https://smap.landcareresearch.co.nz/.
18
1 Introduction