Claremont in Canterbury. We focus on the Claremont site
and outline the soil variation and interconnections along the
chain of soils.
On the summit (interfluve), the soil is wet in winter and
Perch-gley Pallic Soils reign. The wetness is due to slow permeability in the loess at the summit, on near level slopes, which
leads to prolonged periods of saturation. The dominant soils
across the main rolling slopes of the landscape are
Mottled-fragic Pallic Soils. Perch-gley Pallic Soils occur again
further downslope, below the shoulder, where the slope changes
from the convex shoulder to a straight or concave backslope.
Mottled Orthic Recent Soils are recognised on foot-slopes
where sediment has accumulated at the base of the slope,
derived from erosion upslope. The soil at the foot slope
classifies as a Recent Soil because redeposition of material
that has moved downslope has contributed to the topsoil
which is over-thickened to more than 45 cm.
The main pedological processes that provide the genetic
links between the catenary soils are as follows.
• Water flows through the soils both vertically downward
across horizon boundaries, and laterally within horizons,
guided by the shape of the land surface and the soil
porosity. Water influences the movement of solutes and
sediment, and is an important vector of soil formation in
catenas. The catena displays two contrasting forms of
gleying (Chap. 5). On the summits are Perch-gley Pallic
Soils where the water table is perched on slowly permeable subsoil including a fragipan. Permeability measurements have shown values as low as a few millimetres
over a 24-h period. In the shallow valleys are Recent Gley
Soils with over-thickened topsoils due to accumulation of
sediment eroded from the ridges. The Gley Soils are
formed in groundwater fed by water draining from the
rolling loess-covered landscape.
• Sediment is redistributed down the catena by erosion,
especially on shoulder sites where topsoils are thin, and by
sedimentation on lower slopes, especially on the foot slopes
where the topsoil is thick. In similar uncultivated landscapes in the area of the Claremont study, topsoil thicknesses are comparable across all slopes, suggesting that the
topsoil variation may be a result of enhanced erosion and
deposition where and when soil is exposed by ploughing.
• Leaching usually occurs to varying degrees along the
length of a catena, driven by surface water flow and water
penetration through the soil on the slope. The expectation
is that base cations would be higher in the foot slopes but,
interestingly at Claremont, the indicators of leaching
(base saturation, pH, exchangeable cations, and
KCl-extractable Al) do not suggest differential leaching
through the catena. It seems that the base cations have
been leached beyond the foot slopes.
10.4 Key Soil Properties
10.4.1 Soil Composition
Pallic Soils are mainly formed in loess or other fine-grained
sedimentary materials derived from the products of abrasion
and breakdown of schist, greywacke, and mudstone rocks by
energetic river action. The parent materials are dominated by
quartz and feldspars with some mica, particularly from schist
in Otago and Southland. Smaller amounts of fines originated
by glacial grinding or alpine freeze-thaw processes, along
with small inputs of dust blown from Australia. In central
North Island, considerable loess derives from the sediment
eroded from volcanoes and tephra deposits, which give rise
to subsurface tephric loess deposits; however, the soils
formed are generally Allophanic, rather than Pallic.
Weathering of the parent material, concomitant with the
deposition of loess in glacial periods as described earlier, is
low (or moderate at most in higher rainfall areas) because of
the cool wet winters, dry summers, and limited time at the
land surface during loess accumulation. The clay mineralogy
reflects the limited weathering with clays dominated by illite,
little altered from the original mica of the parent material.
Pallic Soils have low concentrations of secondary oxides.
Extractable iron and aluminium values are normally low.
Secondary iron oxides usually occur in redox segregations,
and are not disseminated throughout the bulk of the soil (as
in Brown Soils). Secondary calcium carbonate is notably
low (zero) in most loess deposits in New Zealand although it
does occur in some deposits including in parts of North
Canterbury (Waipawa and Waikari areas) in the Waitaki
Valley, near Timaru, north Otago, and on the flanks of
Banks Peninsula.
10.4.2 Physical Properties
The distinctive soil physical properties of Pallic Soils are
immediately evident in the National Soil Database summaries (Fig. 10.9 and Table 10.1). The very uniform particle
size throughout the profile is illustrated by the clay content
which is consistently about 20%, with most of the remaining
particles in the silt or fine sand category. High total available
water-holding capacity in the upper profile (Fig. 10.9)
indicates high porosity and high available water storage.
However, the marked drop in total water-holding capacity
and accompanying rise in soil dry bulk density with depth
are distinctive. The high lower profile soil dry bulk density
(*1.5 to *1.7 g cm
−3 ) points to the limited pore space at
depth.
Pallic Soils are commonly summer droughty and
winter-spring wet, aggravated by slow subsoil permeability
154
10 Pallic Soils
and outline the soil variation and interconnections along the
chain of soils.
On the summit (interfluve), the soil is wet in winter and
Perch-gley Pallic Soils reign. The wetness is due to slow permeability in the loess at the summit, on near level slopes, which
leads to prolonged periods of saturation. The dominant soils
across the main rolling slopes of the landscape are
Mottled-fragic Pallic Soils. Perch-gley Pallic Soils occur again
further downslope, below the shoulder, where the slope changes
from the convex shoulder to a straight or concave backslope.
Mottled Orthic Recent Soils are recognised on foot-slopes
where sediment has accumulated at the base of the slope,
derived from erosion upslope. The soil at the foot slope
classifies as a Recent Soil because redeposition of material
that has moved downslope has contributed to the topsoil
which is over-thickened to more than 45 cm.
The main pedological processes that provide the genetic
links between the catenary soils are as follows.
• Water flows through the soils both vertically downward
across horizon boundaries, and laterally within horizons,
guided by the shape of the land surface and the soil
porosity. Water influences the movement of solutes and
sediment, and is an important vector of soil formation in
catenas. The catena displays two contrasting forms of
gleying (Chap. 5). On the summits are Perch-gley Pallic
Soils where the water table is perched on slowly permeable subsoil including a fragipan. Permeability measurements have shown values as low as a few millimetres
over a 24-h period. In the shallow valleys are Recent Gley
Soils with over-thickened topsoils due to accumulation of
sediment eroded from the ridges. The Gley Soils are
formed in groundwater fed by water draining from the
rolling loess-covered landscape.
• Sediment is redistributed down the catena by erosion,
especially on shoulder sites where topsoils are thin, and by
sedimentation on lower slopes, especially on the foot slopes
where the topsoil is thick. In similar uncultivated landscapes in the area of the Claremont study, topsoil thicknesses are comparable across all slopes, suggesting that the
topsoil variation may be a result of enhanced erosion and
deposition where and when soil is exposed by ploughing.
• Leaching usually occurs to varying degrees along the
length of a catena, driven by surface water flow and water
penetration through the soil on the slope. The expectation
is that base cations would be higher in the foot slopes but,
interestingly at Claremont, the indicators of leaching
(base saturation, pH, exchangeable cations, and
KCl-extractable Al) do not suggest differential leaching
through the catena. It seems that the base cations have
been leached beyond the foot slopes.
10.4 Key Soil Properties
10.4.1 Soil Composition
Pallic Soils are mainly formed in loess or other fine-grained
sedimentary materials derived from the products of abrasion
and breakdown of schist, greywacke, and mudstone rocks by
energetic river action. The parent materials are dominated by
quartz and feldspars with some mica, particularly from schist
in Otago and Southland. Smaller amounts of fines originated
by glacial grinding or alpine freeze-thaw processes, along
with small inputs of dust blown from Australia. In central
North Island, considerable loess derives from the sediment
eroded from volcanoes and tephra deposits, which give rise
to subsurface tephric loess deposits; however, the soils
formed are generally Allophanic, rather than Pallic.
Weathering of the parent material, concomitant with the
deposition of loess in glacial periods as described earlier, is
low (or moderate at most in higher rainfall areas) because of
the cool wet winters, dry summers, and limited time at the
land surface during loess accumulation. The clay mineralogy
reflects the limited weathering with clays dominated by illite,
little altered from the original mica of the parent material.
Pallic Soils have low concentrations of secondary oxides.
Extractable iron and aluminium values are normally low.
Secondary iron oxides usually occur in redox segregations,
and are not disseminated throughout the bulk of the soil (as
in Brown Soils). Secondary calcium carbonate is notably
low (zero) in most loess deposits in New Zealand although it
does occur in some deposits including in parts of North
Canterbury (Waipawa and Waikari areas) in the Waitaki
Valley, near Timaru, north Otago, and on the flanks of
Banks Peninsula.
10.4.2 Physical Properties
The distinctive soil physical properties of Pallic Soils are
immediately evident in the National Soil Database summaries (Fig. 10.9 and Table 10.1). The very uniform particle
size throughout the profile is illustrated by the clay content
which is consistently about 20%, with most of the remaining
particles in the silt or fine sand category. High total available
water-holding capacity in the upper profile (Fig. 10.9)
indicates high porosity and high available water storage.
However, the marked drop in total water-holding capacity
and accompanying rise in soil dry bulk density with depth
are distinctive. The high lower profile soil dry bulk density
(*1.5 to *1.7 g cm
−3 ) points to the limited pore space at
depth.
Pallic Soils are commonly summer droughty and
winter-spring wet, aggravated by slow subsoil permeability
154
10 Pallic Soils