16
Ultic Soils
Yellow and old, weathered and worn
an Ultic Soil, with time is born
Rich in clay and poor in vigour
farming’s tough and needs some rigour.
Abstract
Ultic Soils are strongly weathered, clay-rich, soils that
form on stable land surfaces, mainly on quartz- and
feldspar-rich parent materials, predominantly in the
northern half of the North Island. Scattered occurrences
also occur on extremely old surfaces in other regions of
New Zealand including Wellington, Marlborough/Nelson, Otago, and Southland. Some Ultic Soils developed
on iron-rich volcanogenic, calcite-bearing sandstones of
Tertiary age in the Auckland-Northland region have
distinct relict reddening in lower subsoils. One subgroup
of the Yellow Ultic Soils in the northern Waikato region
is formed on halloysitic tephra deposits over a buried
clay-rich paleosol. Ultic Soils generally have slow
permeability and are prone to wetness in winter with
attendant risks of compaction or pugging, and are
droughty in summer. They are strongly leached and
naturally acidic (pHs <5.5) with illuvial clay-rich subsoils
and pale-coloured upper subsoils. They have low soil
fertility. Thus substantial additions of lime and fertiliser
are needed for productive use. Ultic Soils are best suited
to pastoral agriculture and forestry. They are an option for
urban development that avoids the more productive soils,
provided the engineering design takes into account the
potential for mud-sliding on the Tertiary sedimentary
rocks (Waitemata Group) in the Auckland-Northland
regions.
16.1 Important Features of Ultic Soils
16.1.1 Concept and Key Features of the Soil
Order
Ultic Soils are strongly weathered, clay-rich, and strongly
leached soils that occur predominantly in the warm, wet,
relatively stable, hill country in northern North Island
(Fig. 16.1) with some occurrences in central and southern
New Zealand. Ultic Soils are generally weathered in place
from quartzofeldspathic basement rocks (usually
greywacke/argillite or schist or Tertiary sedimentary rocks)
as well as from weathered halloysitic tephra in one special
case in the Waikato (Kainui soil). Ultic Soils are the final
soil in a broad climate-dominated weathering and leaching
sequence that proceeds from Semiarid Soils through Pallic
Soils and then Brown Soils to Ultic Soils. However, soils in
some other orders, including (old) Podzol Soils, Granular
Soils, Oxidic Soils, and Aged-argillic Semiarid Soils, may
be of a similar age or similar stage of weathering and/or
leaching (see Chap. 18, Fig. 18.2).
Ultic Soils have a strongly weathered, humus-darkened,
but shallow, topsoil that has a lower clay content than the
underlying well-structured, illuvial clay-enriched, lower
subsoil Bt horizon. Upper subsoils comprise either highly
leached E horizons or pale B horizons with colour values
5 in the transition to the lower clay-rich subsoil. Some E
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_16
249
Ultic Soils
Yellow and old, weathered and worn
an Ultic Soil, with time is born
Rich in clay and poor in vigour
farming’s tough and needs some rigour.
Abstract
Ultic Soils are strongly weathered, clay-rich, soils that
form on stable land surfaces, mainly on quartz- and
feldspar-rich parent materials, predominantly in the
northern half of the North Island. Scattered occurrences
also occur on extremely old surfaces in other regions of
New Zealand including Wellington, Marlborough/Nelson, Otago, and Southland. Some Ultic Soils developed
on iron-rich volcanogenic, calcite-bearing sandstones of
Tertiary age in the Auckland-Northland region have
distinct relict reddening in lower subsoils. One subgroup
of the Yellow Ultic Soils in the northern Waikato region
is formed on halloysitic tephra deposits over a buried
clay-rich paleosol. Ultic Soils generally have slow
permeability and are prone to wetness in winter with
attendant risks of compaction or pugging, and are
droughty in summer. They are strongly leached and
naturally acidic (pHs <5.5) with illuvial clay-rich subsoils
and pale-coloured upper subsoils. They have low soil
fertility. Thus substantial additions of lime and fertiliser
are needed for productive use. Ultic Soils are best suited
to pastoral agriculture and forestry. They are an option for
urban development that avoids the more productive soils,
provided the engineering design takes into account the
potential for mud-sliding on the Tertiary sedimentary
rocks (Waitemata Group) in the Auckland-Northland
regions.
16.1 Important Features of Ultic Soils
16.1.1 Concept and Key Features of the Soil
Order
Ultic Soils are strongly weathered, clay-rich, and strongly
leached soils that occur predominantly in the warm, wet,
relatively stable, hill country in northern North Island
(Fig. 16.1) with some occurrences in central and southern
New Zealand. Ultic Soils are generally weathered in place
from quartzofeldspathic basement rocks (usually
greywacke/argillite or schist or Tertiary sedimentary rocks)
as well as from weathered halloysitic tephra in one special
case in the Waikato (Kainui soil). Ultic Soils are the final
soil in a broad climate-dominated weathering and leaching
sequence that proceeds from Semiarid Soils through Pallic
Soils and then Brown Soils to Ultic Soils. However, soils in
some other orders, including (old) Podzol Soils, Granular
Soils, Oxidic Soils, and Aged-argillic Semiarid Soils, may
be of a similar age or similar stage of weathering and/or
leaching (see Chap. 18, Fig. 18.2).
Ultic Soils have a strongly weathered, humus-darkened,
but shallow, topsoil that has a lower clay content than the
underlying well-structured, illuvial clay-enriched, lower
subsoil Bt horizon. Upper subsoils comprise either highly
leached E horizons or pale B horizons with colour values
5 in the transition to the lower clay-rich subsoil. Some E
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_16
249