m
−2 yr
−1 ) compared to peatlands in many other parts of the
world. They also reported that Kopouatai lost about 14–
22 g m
−2 yr
−1 of carbon in methane to the atmosphere. The
year-round relatively warm, moist climate ensures a greater
rate of plant growth than occurs in much of the northern
hemisphere.
Ratcliffe and others demonstrated that the fallout of
rhyolitic and andesitic tephra has stimulated C accumulation
rates in the Kopouatai bog by increasing the availability of
phosphorus and thus supporting periods of high carbon
uptake. Such phosphorus is potentially derived partly from
fallout of PO 4
3− generated as aerosols during the
tephra-producing eruptions, partly from leachates generated
by aerosol-derived acids attacking particles of volcanic glass
and apatite crystals within the eruption plume, and partly
from the rapid dissolution of tephra-derived glass shards and
apatite that fell on the bog surface.
8.7.3 Management of Organic Soils for Pastoral
Farming and Cropping
Large areas (about 70%) of Organic Soils are utilised in
productive agriculture (Fig. 8.12). Dairy farming is undertaken in the Waikato, and also in other regions including the
Manawatu and Southland. Maize and potato cropping are
also common in Organic Soils. Blueberries are especially
well adapted to peat substrates and New Zealand has a niche
market supplying blueberries to the Northern Hemisphere at
Christmas time.
For agricultural or horticultural use, Organic Soils require
some drainage to enable practical management. However,
drainage will inevitably lead to a loss of the soil resource.
The Waikato Regional Council recommends control of the
water table at a level of 50 cm depth or less in Organic Soils
resources/land-and-soil/managing-land-and-soil/managingpeat/). Deep drains should be avoided as they enhance the
rate of peat subsidence and biodegradation. Also, if peat is
allowed to dry, then it is difficult to get it to rewet and much
rainfall may flow rapidly through cracks in the soil to drains,
and thus be lost to plant production. In summer it may be
beneficial to put weirs or blocks in drains to keep water
tables high and soils moist. Drains will need to be cleared
out less frequently if weeds are controlled (by summer
spraying) and stock are fenced out of drains.
Due to the initial low soil pH, and low nutrient status,
large inputs of lime and fertiliser were applied to establish
productive farming on Organic Soils. A substantial dose of
lime, to raise pH levels from *4 to *5, will be effective for
about four or five years. Both drainage and inputs of fertiliser
enhance microbial activity and thus biodegradation of the
soil resource. Therefore, soil tests need to be undertaken to
determine fertiliser and lime requirements for a given site
and crop in order to avoid the use of more fertiliser than
necessary.
In the long term, agriculture or horticultural development
will lead to degradation of the peat, and lowering of the
ground surface, until the farming/horticultural operation
intercepts the underlying mineral material. This has already
occurred on many farms in parts of the Hauraki Plains and
Hamilton Basin, where the peat has gone with the only
evidence remaining in a ‘peaty topsoil’. Thus farming is now
undertaken in soils formed from the last remnants of the peat
(giving peaty, organic matter-rich, topsoils) and the underlying inorganic sediments. In some regions that are close to
sea level, such as on the Hauraki Plains, to maintain drainage
as the surface subsides, water has to be pumped up, over
river stop-banks into the Waihou and Piako Rivers.
The high carbon content, and anaerobic conditions in
Organic Soils favour denitrification, and so there is a relatively low risk of nitrogen escaping to groundwater, provided that rapid flow through macropores is avoided. Thus
farmed Organic Soils can be suitable for effluent irrigation
during periods when the soil is not saturated to the surface.
Cultivation of Organic Soils greatly increases the rate of
shrinkage and biodegradation compared to that under
established pasture. Thus the less cultivation that is undertaken the longer the peat resource will last. It is preferable to
use no-till (direct drill) methods for pasture renewal or crop
establishment. If ploughing is deemed necessary, it is best to
avoid chopping the peat material finely, which accelerates
biodegradation. Maintaining a dense pasture sward will help
protect the peat. Overgrazing, pugging, or other activities
that leave patches of bare soil exposed, will enhance the
degradation of the organic matter resulting in an uneven
ground surface.
8.7.4 Management of Infrastructure on Organic
Soils
Organic Soils have low bearing strength and are often saturated with water, thus they are generally not suitable for
building infrastructure such as roads and housing without
special engineering design. Wheeled vehicles such as tractors need twin sets of rear wheels and soft tyres to avoid
sinking. The low pH means that concrete and steel may both
be prone to corrosion. If weighty structures are built, the soil
may be compressed unevenly. Roads and railway lines, even
when constructed with large amounts of imported base
materials, are prone to uneven subsidence, which results in
8.7 Use and Management of Organic Soils
129
−2 yr
−1 ) compared to peatlands in many other parts of the
world. They also reported that Kopouatai lost about 14–
22 g m
−2 yr
−1 of carbon in methane to the atmosphere. The
year-round relatively warm, moist climate ensures a greater
rate of plant growth than occurs in much of the northern
hemisphere.
Ratcliffe and others demonstrated that the fallout of
rhyolitic and andesitic tephra has stimulated C accumulation
rates in the Kopouatai bog by increasing the availability of
phosphorus and thus supporting periods of high carbon
uptake. Such phosphorus is potentially derived partly from
fallout of PO 4
3− generated as aerosols during the
tephra-producing eruptions, partly from leachates generated
by aerosol-derived acids attacking particles of volcanic glass
and apatite crystals within the eruption plume, and partly
from the rapid dissolution of tephra-derived glass shards and
apatite that fell on the bog surface.
8.7.3 Management of Organic Soils for Pastoral
Farming and Cropping
Large areas (about 70%) of Organic Soils are utilised in
productive agriculture (Fig. 8.12). Dairy farming is undertaken in the Waikato, and also in other regions including the
Manawatu and Southland. Maize and potato cropping are
also common in Organic Soils. Blueberries are especially
well adapted to peat substrates and New Zealand has a niche
market supplying blueberries to the Northern Hemisphere at
Christmas time.
For agricultural or horticultural use, Organic Soils require
some drainage to enable practical management. However,
drainage will inevitably lead to a loss of the soil resource.
The Waikato Regional Council recommends control of the
water table at a level of 50 cm depth or less in Organic Soils
resources/land-and-soil/managing-land-and-soil/managingpeat/). Deep drains should be avoided as they enhance the
rate of peat subsidence and biodegradation. Also, if peat is
allowed to dry, then it is difficult to get it to rewet and much
rainfall may flow rapidly through cracks in the soil to drains,
and thus be lost to plant production. In summer it may be
beneficial to put weirs or blocks in drains to keep water
tables high and soils moist. Drains will need to be cleared
out less frequently if weeds are controlled (by summer
spraying) and stock are fenced out of drains.
Due to the initial low soil pH, and low nutrient status,
large inputs of lime and fertiliser were applied to establish
productive farming on Organic Soils. A substantial dose of
lime, to raise pH levels from *4 to *5, will be effective for
about four or five years. Both drainage and inputs of fertiliser
enhance microbial activity and thus biodegradation of the
soil resource. Therefore, soil tests need to be undertaken to
determine fertiliser and lime requirements for a given site
and crop in order to avoid the use of more fertiliser than
necessary.
In the long term, agriculture or horticultural development
will lead to degradation of the peat, and lowering of the
ground surface, until the farming/horticultural operation
intercepts the underlying mineral material. This has already
occurred on many farms in parts of the Hauraki Plains and
Hamilton Basin, where the peat has gone with the only
evidence remaining in a ‘peaty topsoil’. Thus farming is now
undertaken in soils formed from the last remnants of the peat
(giving peaty, organic matter-rich, topsoils) and the underlying inorganic sediments. In some regions that are close to
sea level, such as on the Hauraki Plains, to maintain drainage
as the surface subsides, water has to be pumped up, over
river stop-banks into the Waihou and Piako Rivers.
The high carbon content, and anaerobic conditions in
Organic Soils favour denitrification, and so there is a relatively low risk of nitrogen escaping to groundwater, provided that rapid flow through macropores is avoided. Thus
farmed Organic Soils can be suitable for effluent irrigation
during periods when the soil is not saturated to the surface.
Cultivation of Organic Soils greatly increases the rate of
shrinkage and biodegradation compared to that under
established pasture. Thus the less cultivation that is undertaken the longer the peat resource will last. It is preferable to
use no-till (direct drill) methods for pasture renewal or crop
establishment. If ploughing is deemed necessary, it is best to
avoid chopping the peat material finely, which accelerates
biodegradation. Maintaining a dense pasture sward will help
protect the peat. Overgrazing, pugging, or other activities
that leave patches of bare soil exposed, will enhance the
degradation of the organic matter resulting in an uneven
ground surface.
8.7.4 Management of Infrastructure on Organic
Soils
Organic Soils have low bearing strength and are often saturated with water, thus they are generally not suitable for
building infrastructure such as roads and housing without
special engineering design. Wheeled vehicles such as tractors need twin sets of rear wheels and soft tyres to avoid
sinking. The low pH means that concrete and steel may both
be prone to corrosion. If weighty structures are built, the soil
may be compressed unevenly. Roads and railway lines, even
when constructed with large amounts of imported base
materials, are prone to uneven subsidence, which results in
8.7 Use and Management of Organic Soils
129