Firm Brown Soils have a subsoil layer that is frequently
slowly permeable and may be an impediment for some deep
rooting plants. However, in the Southland lowlands, Firm
Brown Soils are a productive mainstay for a range of pastoral or cropping uses. Subsurface drainage is often installed
on Firm Brown Soils, in flatter areas, providing long-term
improvement in soil productivity and improved resilience to
pugging damage during wet periods.
Orthic Brown Soils are widely used for pastoral agriculture. They have few productive limitations, other than fertility requirements, and lack the firm subsoil layers of the
Firm Brown Soils.
4.7.2 Soil Fertility
Pastoral farming on Brown Soils across the extensive hill
country is one of New Zealand’s major land uses. Pastoral
farming was made possible with the advent of aerial topdressing, from around 1946, which provided a key to the
productivity of hill country farms, both for initial development and continuing maintenance. The advent of aerial
topdressing was a major boost to production in the hill
country as nutrient deficiencies could be readily remedied,
low pH addressed, and the nutrients removed in products
could be efficiently replaced to ensure a sustainable farming
system could be developed. The improved pasture cover also
helps reduce erosion.
Many Brown Soils, and particularly the Acid Brown
Soils, respond to addition of lime. Phosphorus fertilisers are
regularly applied to build or maintain productivity and to
support the clover-based pastures where clover provides a
source of nitrogen. As with all fertiliser use, soil sampling
and analysis should be undertaken to determine the soil
nutrient status and needs of the site prior to any fertiliser
addition.
Potential for nutrient, along with sediment, runoff from
hill country is gaining wide attention and a number of
mechanisms may be considered to maximise fertiliser use
efficiency and minimise loss (and wastage of expensive
fertiliser materials) to runoff. Where practical, stream riparian fencing with a good grass cover to filter sediment and
nutrients from runoff can be effective. Use of improved GPS
in aircraft can ensure that fertiliser is placed on productive
areas, and stream gullies and unproductive areas are avoided.
Ideally, fertilisers should be applied ahead of gentle rainfall
to maximise fertiliser movement into the soil, but not ahead
of high intensity storms where runoff is likely.
4.7.3 Hill Country Erosion
One of the major issues of the hill and steepland is hillslope
erosion. Some of New Zealand’s worst hillslope erosion
occurs on the mudstone hill country in higher rainfall areas
where Brown Soils often predominate, particularly on the
east coast of the North Island from the Wairarapa through to
East Cape, and in the Whanganui and Rangitikei River
catchments. Periodic high intensity rainstorms have caused a
long history of severe erosion events. A series of storms in
the 1930s first brought erosion of the North Island east coast
hill country to national attention and Cyclone Bola, in March
1988, caused catastrophic damage across the Gisborne-East
Cape area. About 20% of the land surface was affected.
Similar effects were seen in the southern North Island in
February 2004 when a severe storm resulted in widespread
erosion. The hill country is also prone to major earthquakes
that may set off large-scale slumping and landslides.
Workers from Landcare Research and AgResearch have
shown that in the south Wairarapa pasture production on
eroded sites recovered reasonably rapidly in the first 20–
30 years after a landslide event but was unlikely to recover
to more than about 80% of the production on non-eroded
sites.
To some degree the erosion of the soft rock hill country is
an ongoing geologic process (Fig. 4.7), but it has been
shown that erosion, in major rainfall events, is greater under
grass than forest vegetation. Some of the steeper, most
erosion prone, areas are probably best left to revert to native
forest vegetation. Forestry is an option across virtually all the
Brown Soils. Where pastoral agriculture is the preferred land
use, much can be done to prevent or minimise erosion
effects. Retirement, or reforestation, of steep slopes and
stream margins is a good option that also contributes to
biodiversity. Use of simple debris dams within gullies to
prevent ongoing stream down-cutting and undermining of
foot slopes can help. Paired willow planting in association
with small debris dams has provided effective medium-term
gully control. Flood detention dams and establishment of
wetland areas at the foot of slopes to intercept and filter
runoff before it reaches a watercourse can greatly enhance
the quality of runoff water. Slope stabilisation using scattered tree planting, often using poplars, has been effective in
stabilising many slopes. Suitable tree species may also be
trimmed to provide fodder for animals during summer
droughts. Improved soil fertility and strong pasture growth
also help prevent surface soil erosion; however, careful stock
management is needed as the benefits may be counteracted
4.7 Use and Management of Brown Soils
69
slowly permeable and may be an impediment for some deep
rooting plants. However, in the Southland lowlands, Firm
Brown Soils are a productive mainstay for a range of pastoral or cropping uses. Subsurface drainage is often installed
on Firm Brown Soils, in flatter areas, providing long-term
improvement in soil productivity and improved resilience to
pugging damage during wet periods.
Orthic Brown Soils are widely used for pastoral agriculture. They have few productive limitations, other than fertility requirements, and lack the firm subsoil layers of the
Firm Brown Soils.
4.7.2 Soil Fertility
Pastoral farming on Brown Soils across the extensive hill
country is one of New Zealand’s major land uses. Pastoral
farming was made possible with the advent of aerial topdressing, from around 1946, which provided a key to the
productivity of hill country farms, both for initial development and continuing maintenance. The advent of aerial
topdressing was a major boost to production in the hill
country as nutrient deficiencies could be readily remedied,
low pH addressed, and the nutrients removed in products
could be efficiently replaced to ensure a sustainable farming
system could be developed. The improved pasture cover also
helps reduce erosion.
Many Brown Soils, and particularly the Acid Brown
Soils, respond to addition of lime. Phosphorus fertilisers are
regularly applied to build or maintain productivity and to
support the clover-based pastures where clover provides a
source of nitrogen. As with all fertiliser use, soil sampling
and analysis should be undertaken to determine the soil
nutrient status and needs of the site prior to any fertiliser
addition.
Potential for nutrient, along with sediment, runoff from
hill country is gaining wide attention and a number of
mechanisms may be considered to maximise fertiliser use
efficiency and minimise loss (and wastage of expensive
fertiliser materials) to runoff. Where practical, stream riparian fencing with a good grass cover to filter sediment and
nutrients from runoff can be effective. Use of improved GPS
in aircraft can ensure that fertiliser is placed on productive
areas, and stream gullies and unproductive areas are avoided.
Ideally, fertilisers should be applied ahead of gentle rainfall
to maximise fertiliser movement into the soil, but not ahead
of high intensity storms where runoff is likely.
4.7.3 Hill Country Erosion
One of the major issues of the hill and steepland is hillslope
erosion. Some of New Zealand’s worst hillslope erosion
occurs on the mudstone hill country in higher rainfall areas
where Brown Soils often predominate, particularly on the
east coast of the North Island from the Wairarapa through to
East Cape, and in the Whanganui and Rangitikei River
catchments. Periodic high intensity rainstorms have caused a
long history of severe erosion events. A series of storms in
the 1930s first brought erosion of the North Island east coast
hill country to national attention and Cyclone Bola, in March
1988, caused catastrophic damage across the Gisborne-East
Cape area. About 20% of the land surface was affected.
Similar effects were seen in the southern North Island in
February 2004 when a severe storm resulted in widespread
erosion. The hill country is also prone to major earthquakes
that may set off large-scale slumping and landslides.
Workers from Landcare Research and AgResearch have
shown that in the south Wairarapa pasture production on
eroded sites recovered reasonably rapidly in the first 20–
30 years after a landslide event but was unlikely to recover
to more than about 80% of the production on non-eroded
sites.
To some degree the erosion of the soft rock hill country is
an ongoing geologic process (Fig. 4.7), but it has been
shown that erosion, in major rainfall events, is greater under
grass than forest vegetation. Some of the steeper, most
erosion prone, areas are probably best left to revert to native
forest vegetation. Forestry is an option across virtually all the
Brown Soils. Where pastoral agriculture is the preferred land
use, much can be done to prevent or minimise erosion
effects. Retirement, or reforestation, of steep slopes and
stream margins is a good option that also contributes to
biodiversity. Use of simple debris dams within gullies to
prevent ongoing stream down-cutting and undermining of
foot slopes can help. Paired willow planting in association
with small debris dams has provided effective medium-term
gully control. Flood detention dams and establishment of
wetland areas at the foot of slopes to intercept and filter
runoff before it reaches a watercourse can greatly enhance
the quality of runoff water. Slope stabilisation using scattered tree planting, often using poplars, has been effective in
stabilising many slopes. Suitable tree species may also be
trimmed to provide fodder for animals during summer
droughts. Improved soil fertility and strong pasture growth
also help prevent surface soil erosion; however, careful stock
management is needed as the benefits may be counteracted
4.7 Use and Management of Brown Soils
69