that water added to the soil during rainfall all seeps into the
soil with no surface runoff (and consequently few surface
streams). However, topsoils under pasture have a lower
content of large pores than topsoils under forest, making the
soils more vulnerable to runoff, especially where vehicle or
stock trampling has increased soil compaction, leading to
potential for erosion and thus sediment and nutrient losses.
In the 1970s, Michael Selby examined runoff from
Pumice Soils under pasture grass, un-grazed grass, and
scrub. Climatic, soil, vegetation, and slope variables were
evaluated. Surface water runoff, caused by intense rainfall,
coupled with low soil moisture content, was found to be
greater on developed pasture than on un-grazed grasslands
or scrub. The runoff was exacerbated where soils had been
compacted by animals or vehicles. In spite of the greater
inherent erodibility of soil under scrub, due to higher runoff,
the actual erosion was found to be greater on pasture lands.
Factor analyses showed that the high porosity and low
density of the pumice, the soil’s degree of aggregation, and
the soil organic matter content together accounted for 83%
of the erosion variability.
One heavy rainstorm, which causes runoff on exposed soil,
can result in large volumes of soil removal and rapid formation
of steep-sided gullies. Gully erosion is attributable largely to
the low density and easy entrainment of pumice particles.
Thus the erosion of Pumice Soils can be rapid if vegetation is
removed and the soil is exposed to running water in which
pumice floats. Hence, it is recommended that vegetation
cover, preferably using plants with strong, dense, root systems, is maintained to protect surface soils. If a pasture
renewal programme is to be undertaken it is strongly recommended to use no tillage. Instead, direct drill to protect the soil
from erosion. Topsoils are relatively resistant to compaction,
but treading damage can occur under grazing with reduction of
macroporosity and thus increased risk of water runoff and
potential for erosion if vegetation cover is not strong. Vulnerable areas such as valley floors and steep valley sides can be
protected as water-absorption areas (planted in trees for
example) with animals and vehicles excluded to prevent soil
compaction. Extra care has to be taken when managing construction sites or road margins to prevent channel development
and runoff water from causing severe damage.
12.7.5 Developments on Pumice Soils
in the Twenty-First Century
Land use change on Pumice Soils has occurred at pace since
the late 1990s through intensification of current pastoral
systems (e.g. drystock to dairying) and the conversion of
established plantation forests to pasture, most commonly for
dairying. Conversion was driven by the perceived better
economic returns from farming compared with forestry.
Large-scale conversion of established plantation forest to
pasture occurred, primarily in the Waikato River catchment,
between Taupo and Lake Karapiro.
The main environmental impact is from the increased
losses of nitrogen and, to a lesser extent, phosphorus, into
ground and surface waters. At the same time, the change in
land use from plantation forest to dairy pasture on Pumice
Soils has resulted in a moderate increase or no change in soil
storage of carbon. Regional council staff and others have
been working with farmers, iwi, and other stakeholders to
develop new ways of managing farms to mitigate environmental degradation.
Treated wastewater from Taupo town is successfully
irrigated onto Pumice Soils. The phosphate (or anion)
retention capacity assists in preventing leaching of phosphates and other anions from effluents. In well-drained
Pumice Soils, nitrate may readily leach from the soil profile.
However, Glen Trewick and Erin Telfer showed that at the
Taupo town wastewater irrigation site, pasture harvest and
export removed at least 80% of applied nitrogen from the
site with pasture production two to three times higher under
effluent irrigation than unirrigated controls. The mean concentration of nitrate in water reaching the subsoil was
1.3 g N m
−3 , considerably below the Ministry of Health
guideline limit of 11.3 g N m
−3 . Perch-gley Pumice Soils
will have seasonally anaerobic conditions which support
denitrification and thus further reduce risk of nitrate leaching
to groundwater.
Further Reading
Anon (1935) Cobalt and ‘coast disease’ of sheep in Australia. Nature
135:518
Askew HO, Dixon JK (1937) Influence of cobalt top-dressing on the
cobalt status of pasture plants. New Zealand J Sci Technol l8:688–
693
Aston BC (1911) The chemistry of bush sickness. Trans Proc New
Zealand Inst 44:288–298
Aston BC (1924) The chemistry of bush sickness, or iron starvation, in
ruminants. Trans Proc New Zealand Inst 55:720–723
Barker SJ, Wilson CJN, Illsley-Kemp F et al (2021) Taupō: an
overview of New Zealand’s youngest supervolcano. NZ J Geol
Geophys. https://doi.org/10.1080/00288306.2020.1792515
Brink NG, Kuehl FA Jr, Folkers K (1950) Vitamin B 12 : the
identification of vitamin B 12 as a cyano-cobalt coordination
complex. Science 112:354
Dixon JK (1936) Investigation of a sheep ailment in Southland. New
Zealand J Sci Technol 17:600–619
Dixon JK (1936–37) Mineral content of pastures. Report on Morton
Mains investigations. New Zealand Department of Scientific and
Industrial Research Annual Report 11:47–49
Eden DN (1992) A standard method for determining volcanic glass
content in Andisols. New Zealand Department of Scientific and
Industrial Research Land Resources Scientific Report 2
Filmer JR, Underwood EJ (1934) Enzootic marasmus. Treatment with
limonite fractions. Aust Vet J 10:83–87
196
12 Pumice Soils
soil with no surface runoff (and consequently few surface
streams). However, topsoils under pasture have a lower
content of large pores than topsoils under forest, making the
soils more vulnerable to runoff, especially where vehicle or
stock trampling has increased soil compaction, leading to
potential for erosion and thus sediment and nutrient losses.
In the 1970s, Michael Selby examined runoff from
Pumice Soils under pasture grass, un-grazed grass, and
scrub. Climatic, soil, vegetation, and slope variables were
evaluated. Surface water runoff, caused by intense rainfall,
coupled with low soil moisture content, was found to be
greater on developed pasture than on un-grazed grasslands
or scrub. The runoff was exacerbated where soils had been
compacted by animals or vehicles. In spite of the greater
inherent erodibility of soil under scrub, due to higher runoff,
the actual erosion was found to be greater on pasture lands.
Factor analyses showed that the high porosity and low
density of the pumice, the soil’s degree of aggregation, and
the soil organic matter content together accounted for 83%
of the erosion variability.
One heavy rainstorm, which causes runoff on exposed soil,
can result in large volumes of soil removal and rapid formation
of steep-sided gullies. Gully erosion is attributable largely to
the low density and easy entrainment of pumice particles.
Thus the erosion of Pumice Soils can be rapid if vegetation is
removed and the soil is exposed to running water in which
pumice floats. Hence, it is recommended that vegetation
cover, preferably using plants with strong, dense, root systems, is maintained to protect surface soils. If a pasture
renewal programme is to be undertaken it is strongly recommended to use no tillage. Instead, direct drill to protect the soil
from erosion. Topsoils are relatively resistant to compaction,
but treading damage can occur under grazing with reduction of
macroporosity and thus increased risk of water runoff and
potential for erosion if vegetation cover is not strong. Vulnerable areas such as valley floors and steep valley sides can be
protected as water-absorption areas (planted in trees for
example) with animals and vehicles excluded to prevent soil
compaction. Extra care has to be taken when managing construction sites or road margins to prevent channel development
and runoff water from causing severe damage.
12.7.5 Developments on Pumice Soils
in the Twenty-First Century
Land use change on Pumice Soils has occurred at pace since
the late 1990s through intensification of current pastoral
systems (e.g. drystock to dairying) and the conversion of
established plantation forests to pasture, most commonly for
dairying. Conversion was driven by the perceived better
economic returns from farming compared with forestry.
Large-scale conversion of established plantation forest to
pasture occurred, primarily in the Waikato River catchment,
between Taupo and Lake Karapiro.
The main environmental impact is from the increased
losses of nitrogen and, to a lesser extent, phosphorus, into
ground and surface waters. At the same time, the change in
land use from plantation forest to dairy pasture on Pumice
Soils has resulted in a moderate increase or no change in soil
storage of carbon. Regional council staff and others have
been working with farmers, iwi, and other stakeholders to
develop new ways of managing farms to mitigate environmental degradation.
Treated wastewater from Taupo town is successfully
irrigated onto Pumice Soils. The phosphate (or anion)
retention capacity assists in preventing leaching of phosphates and other anions from effluents. In well-drained
Pumice Soils, nitrate may readily leach from the soil profile.
However, Glen Trewick and Erin Telfer showed that at the
Taupo town wastewater irrigation site, pasture harvest and
export removed at least 80% of applied nitrogen from the
site with pasture production two to three times higher under
effluent irrigation than unirrigated controls. The mean concentration of nitrate in water reaching the subsoil was
1.3 g N m
−3 , considerably below the Ministry of Health
guideline limit of 11.3 g N m
−3 . Perch-gley Pumice Soils
will have seasonally anaerobic conditions which support
denitrification and thus further reduce risk of nitrate leaching
to groundwater.
Further Reading
Anon (1935) Cobalt and ‘coast disease’ of sheep in Australia. Nature
135:518
Askew HO, Dixon JK (1937) Influence of cobalt top-dressing on the
cobalt status of pasture plants. New Zealand J Sci Technol l8:688–
693
Aston BC (1911) The chemistry of bush sickness. Trans Proc New
Zealand Inst 44:288–298
Aston BC (1924) The chemistry of bush sickness, or iron starvation, in
ruminants. Trans Proc New Zealand Inst 55:720–723
Barker SJ, Wilson CJN, Illsley-Kemp F et al (2021) Taupō: an
overview of New Zealand’s youngest supervolcano. NZ J Geol
Geophys. https://doi.org/10.1080/00288306.2020.1792515
Brink NG, Kuehl FA Jr, Folkers K (1950) Vitamin B 12 : the
identification of vitamin B 12 as a cyano-cobalt coordination
complex. Science 112:354
Dixon JK (1936) Investigation of a sheep ailment in Southland. New
Zealand J Sci Technol 17:600–619
Dixon JK (1936–37) Mineral content of pastures. Report on Morton
Mains investigations. New Zealand Department of Scientific and
Industrial Research Annual Report 11:47–49
Eden DN (1992) A standard method for determining volcanic glass
content in Andisols. New Zealand Department of Scientific and
Industrial Research Land Resources Scientific Report 2
Filmer JR, Underwood EJ (1934) Enzootic marasmus. Treatment with
limonite fractions. Aust Vet J 10:83–87
196
12 Pumice Soils