16.7 Use and Management of Ultic Soils
The strongly weathered Ultic Soils have clayey subsoils,
slow permeability, low soil fertility, and low water holding
capacity, which, along with winter wetness and summer
drought, means the soils are usually challenging to use
productively. With lime and fertiliser inputs, the soils will
support pastural agriculture. Many of the Ultic Soils occur
on sloping hill country and therefore are not well suited to
more intensive horticultural production or cropping due to
erosion risk in ploughed fields. Thus, sheep and cattle
grazing are the dominant land uses as well as forestry.
For sheep and beef farming, once soil fertility has been
built up, maintenance fertiliser will be needed to replace
nutrients removed with the products (mainly wool and
meat). Because the soils have slow permeability, they are
prone to becoming waterlogged in periods of high rainfall
(in winter and early spring). The dispersive tendency of A
and E horizons enhances susceptibility to livestock-treading
damage and erosion. Thus, when grazing cattle, care needs
to be taken to prevent pugging which leads to bare ground at
the soil surface with consequent erosion, weed invasion of
pasture, and loss of productivity.
Trampling of wet soils can also cause compaction and
sealing of the soil surface which promotes runoff and, thus,
increased erosion and sediment carried to downslope water
bodies. Management options include ensuring stocking rates
are low enough to prevent damage, or to graze an area for a
part of the day then move stock to stand-off pads where
effluent must be appropriately managed. Sheep may be a
better option for grazing the steeper hill country as they do
not damage the ground surface as much as heavy cattle.
Riparian fencing and appropriate riparian vegetation can
help trap sediments and nutrient runoff, thus protecting
stream water quality.
Ultic Soils can be used for urban or peri-urban development which provides a good alternative for city expansion,
avoiding other more productive soil. For urban development,
slopes may need some recontouring and people should be
encouraged to replace topsoil on the new land surfaces
where they want to establish gardens. The ‘yellow clay’ of
Ultic Soil subsoils is well known to developers and Auckland gardeners. It is acidic and hard in summer and very wet
in winter. Lime can correct the acidity but needs to be
mechanically incorporated to correct subsoil acidity, and
compost can be dug-in to help correct the heavy clayinfluenced structure.
Care must be taken when establishing expensive urban
infrastructure on Ultic Soils because many slopes are prone
to mudslides (also called earthflows), and landslides, particularly those on the Waitemata Group sedimentary rocks in
the Auckland/Northland region (Fig. 16.11). The high proportions of swelling clays can lead to the formation of
contraction cracks during dry periods. The cracks allow
rapid infiltration of water into the soil but drainage from the
soil profile is very slow. The clayey soil material becomes
saturated and, where it overlies a gently dipping rock surface
and with low shear strength, failure occurs along a basal
shear surface at the soil/bedrock contact. Modelling undertaken by Vicki Moon showed that failure was initiated on
slopes of 15–20 degrees. It is also evident that ‘slow mudslide activity’, a type of soil creep, has occurred in some
developed urban areas on Ultic Soils in the Auckland region.
That the landscape is eroding and slowly but surely
downwearing is highlighted by the sediment yields from
rivers such as the Wairoa River near Dargaville, which
carries an average sediment load of 1.1 Mt per year. Severe
Table 16.4 Correlation
a
between Ultic Soils and
equivalent classes of Soil
Taxonomy, World Reference
Base, and the New Zealand
genetic soil classification
New Zealand
Soil
Classification
Soil Taxonomy
World
Reference
Base
NZ genetic soil
classification
Densipan Ultic
Soils
Albaquults, Epiaquults
Endogleyic
Planosols
Albic Ultic
Soils
Albaquults
Planosols
(Albic)
Northern
yellow-brown
earths
Perch-gley
Ultic Soils
Kandic Albaquults, Aeric Epiaquults
Epigleyic
Planosols
Gley soils
Sandy Ultic
Soils
Haplohumults
Planosols
(Arenic)
Yellow-brown
earths
Yellow Ultic
Soils
Kandihumults, Typic Kandiudults, Typic
Hapludults, Typic Paleudults, Aeric Paleaquults,
Aeric Endoaquults
Haplic
Planosols
Northern
yellow-brown
earths
a The correlations given here are a guide only and, for accurate classifications, the relevant soil classification
documents should be consulted. The two major international soil classification systems are Soil Taxonomy,
which was developed initially in the USA, and World Reference Base, which was developed primarily in
Europe. The NZ genetic soil classification was used in New Zealand prior to 1992
262
16 Ultic Soils
The strongly weathered Ultic Soils have clayey subsoils,
slow permeability, low soil fertility, and low water holding
capacity, which, along with winter wetness and summer
drought, means the soils are usually challenging to use
productively. With lime and fertiliser inputs, the soils will
support pastural agriculture. Many of the Ultic Soils occur
on sloping hill country and therefore are not well suited to
more intensive horticultural production or cropping due to
erosion risk in ploughed fields. Thus, sheep and cattle
grazing are the dominant land uses as well as forestry.
For sheep and beef farming, once soil fertility has been
built up, maintenance fertiliser will be needed to replace
nutrients removed with the products (mainly wool and
meat). Because the soils have slow permeability, they are
prone to becoming waterlogged in periods of high rainfall
(in winter and early spring). The dispersive tendency of A
and E horizons enhances susceptibility to livestock-treading
damage and erosion. Thus, when grazing cattle, care needs
to be taken to prevent pugging which leads to bare ground at
the soil surface with consequent erosion, weed invasion of
pasture, and loss of productivity.
Trampling of wet soils can also cause compaction and
sealing of the soil surface which promotes runoff and, thus,
increased erosion and sediment carried to downslope water
bodies. Management options include ensuring stocking rates
are low enough to prevent damage, or to graze an area for a
part of the day then move stock to stand-off pads where
effluent must be appropriately managed. Sheep may be a
better option for grazing the steeper hill country as they do
not damage the ground surface as much as heavy cattle.
Riparian fencing and appropriate riparian vegetation can
help trap sediments and nutrient runoff, thus protecting
stream water quality.
Ultic Soils can be used for urban or peri-urban development which provides a good alternative for city expansion,
avoiding other more productive soil. For urban development,
slopes may need some recontouring and people should be
encouraged to replace topsoil on the new land surfaces
where they want to establish gardens. The ‘yellow clay’ of
Ultic Soil subsoils is well known to developers and Auckland gardeners. It is acidic and hard in summer and very wet
in winter. Lime can correct the acidity but needs to be
mechanically incorporated to correct subsoil acidity, and
compost can be dug-in to help correct the heavy clayinfluenced structure.
Care must be taken when establishing expensive urban
infrastructure on Ultic Soils because many slopes are prone
to mudslides (also called earthflows), and landslides, particularly those on the Waitemata Group sedimentary rocks in
the Auckland/Northland region (Fig. 16.11). The high proportions of swelling clays can lead to the formation of
contraction cracks during dry periods. The cracks allow
rapid infiltration of water into the soil but drainage from the
soil profile is very slow. The clayey soil material becomes
saturated and, where it overlies a gently dipping rock surface
and with low shear strength, failure occurs along a basal
shear surface at the soil/bedrock contact. Modelling undertaken by Vicki Moon showed that failure was initiated on
slopes of 15–20 degrees. It is also evident that ‘slow mudslide activity’, a type of soil creep, has occurred in some
developed urban areas on Ultic Soils in the Auckland region.
That the landscape is eroding and slowly but surely
downwearing is highlighted by the sediment yields from
rivers such as the Wairoa River near Dargaville, which
carries an average sediment load of 1.1 Mt per year. Severe
Table 16.4 Correlation
a
between Ultic Soils and
equivalent classes of Soil
Taxonomy, World Reference
Base, and the New Zealand
genetic soil classification
New Zealand
Soil
Classification
Soil Taxonomy
World
Reference
Base
NZ genetic soil
classification
Densipan Ultic
Soils
Albaquults, Epiaquults
Endogleyic
Planosols
Albic Ultic
Soils
Albaquults
Planosols
(Albic)
Northern
yellow-brown
earths
Perch-gley
Ultic Soils
Kandic Albaquults, Aeric Epiaquults
Epigleyic
Planosols
Gley soils
Sandy Ultic
Soils
Haplohumults
Planosols
(Arenic)
Yellow-brown
earths
Yellow Ultic
Soils
Kandihumults, Typic Kandiudults, Typic
Hapludults, Typic Paleudults, Aeric Paleaquults,
Aeric Endoaquults
Haplic
Planosols
Northern
yellow-brown
earths
a The correlations given here are a guide only and, for accurate classifications, the relevant soil classification
documents should be consulted. The two major international soil classification systems are Soil Taxonomy,
which was developed initially in the USA, and World Reference Base, which was developed primarily in
Europe. The NZ genetic soil classification was used in New Zealand prior to 1992
262
16 Ultic Soils