15
Semiarid Soils
In the drylands of Central Otago
on Semiarid Soils thyme doth grow.
Through summer sun and winter
frost all moisture to the air is lost.
Abstract
Semiarid Soils form in the inland basins of Central Otago
and South Canterbury under rainfalls of less than about
500 mm yr
−1 . The soils have an annual moisture deficit
with hot summers and cold winters. Parent materials are
predominantly alluvium, colluvium, and loess derived
from greywacke and schist. Semiarid Soils range from
immature gravelly sandy soils, on low terraces, to
moderately weathered soils with clay accumulation on
older, higher, terraces, fans, and hills. Accumulations of
salts and illuvial clays can occur in subsoils. Pockets of
Solonetzic Semiarid Soils occur with high pH (>8.5) and
sufficient sodium to preclude the growth of plants, except
for a few specially adapted salt-tolerant plant species.
With irrigation, Semiarid Soils can be developed for
productive agriculture and horticulture. Stone fruit,
including apricots and cherries targeting the Northern
Hemisphere Christmas market, and grape growing for
wine production are important industries in the region,
along with merino fine wool. Although there has been
concern about the potential for irrigation to cause
salinisation, such fears have proven largely unfounded
as the plentiful use of high-quality water, from the major
rivers that flow through the region, along with good
drainage, has tended to wash any salts from the soil.
15.1 Important Features of Semiarid Soils
15.1.1 Concept and Key Features of the Soil
Order
Semiarid Soils (Fig. 15.1) form in the driest regions of New
Zealand with rainfall ranging from about 300 to 500 mm per
year. Semiarid Soils generally lack a strongly developed
topsoil. However, many profiles show evidence of salt and/or
clay accumulation. The presence of visible salts (e.g.
Fig. 15.1 centre) is an indicator of the semiarid character of
the soils. The Semiarid Soils (with some minor exceptions in
north and south Canterbury) are the only soils in New Zealand
where there is potential for significant natural salt accumulation. On some higher terraces, the soil is likely to be very old,
possibly of the order of c. 350,000 years or so (e.g. Fig. 15.1
right). The clay in such soils is considered to be a very old,
relict feature, and the marked dark reddish brown
clay-enriched argillic horizon between 35 and 60 cm depth is
a paleosol. Stoniness is common but there are areas of deep
soils with few or no stones that have a high capacity to store
water and so respond well to irrigation.
Much of the early soil science investigation in Central
Otago was undertaken, particularly by John McCraw and
Michael Leamy, to ensure that the development of irrigation
© 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_15
231
Semiarid Soils
In the drylands of Central Otago
on Semiarid Soils thyme doth grow.
Through summer sun and winter
frost all moisture to the air is lost.
Abstract
Semiarid Soils form in the inland basins of Central Otago
and South Canterbury under rainfalls of less than about
500 mm yr
−1 . The soils have an annual moisture deficit
with hot summers and cold winters. Parent materials are
predominantly alluvium, colluvium, and loess derived
from greywacke and schist. Semiarid Soils range from
immature gravelly sandy soils, on low terraces, to
moderately weathered soils with clay accumulation on
older, higher, terraces, fans, and hills. Accumulations of
salts and illuvial clays can occur in subsoils. Pockets of
Solonetzic Semiarid Soils occur with high pH (>8.5) and
sufficient sodium to preclude the growth of plants, except
for a few specially adapted salt-tolerant plant species.
With irrigation, Semiarid Soils can be developed for
productive agriculture and horticulture. Stone fruit,
including apricots and cherries targeting the Northern
Hemisphere Christmas market, and grape growing for
wine production are important industries in the region,
along with merino fine wool. Although there has been
concern about the potential for irrigation to cause
salinisation, such fears have proven largely unfounded
as the plentiful use of high-quality water, from the major
rivers that flow through the region, along with good
drainage, has tended to wash any salts from the soil.
15.1 Important Features of Semiarid Soils
15.1.1 Concept and Key Features of the Soil
Order
Semiarid Soils (Fig. 15.1) form in the driest regions of New
Zealand with rainfall ranging from about 300 to 500 mm per
year. Semiarid Soils generally lack a strongly developed
topsoil. However, many profiles show evidence of salt and/or
clay accumulation. The presence of visible salts (e.g.
Fig. 15.1 centre) is an indicator of the semiarid character of
the soils. The Semiarid Soils (with some minor exceptions in
north and south Canterbury) are the only soils in New Zealand
where there is potential for significant natural salt accumulation. On some higher terraces, the soil is likely to be very old,
possibly of the order of c. 350,000 years or so (e.g. Fig. 15.1
right). The clay in such soils is considered to be a very old,
relict feature, and the marked dark reddish brown
clay-enriched argillic horizon between 35 and 60 cm depth is
a paleosol. Stoniness is common but there are areas of deep
soils with few or no stones that have a high capacity to store
water and so respond well to irrigation.
Much of the early soil science investigation in Central
Otago was undertaken, particularly by John McCraw and
Michael Leamy, to ensure that the development of irrigation
© 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_15
231