Country Pasture/Forage Resource Profiles
New Zealand

By

Derrick Moot, Annamaria Mills, Dick Lucas and Warwick Scott


1. INTRODUCTION
Location and land area
Current population and distribution
Natural resources and the exclusive economic zone
Natural hazards
Farming area, ruminant numbers and main breeds
Exports
Natural History
Native flora and fauna
Maori colonisation
Post-human species introductions
Conservation and biosecurity
Tourism
European colonisation and agricultural development
European colonisation
Agricultural development

2. SOILS AND TOPOGRAPHY
Major topographic features
Soils
Soil classification
Soil erosion

3. CLIMATE and AGRO-ECOLOGICAL ZONES
Climate
Temperature
Rainfall
Potential evapotranspiration and potential soil moisture deficits
Winds
Frost and snow events
Agro-ecological zones
Arable and horticultural production

4. RUMINANT LIVESTOCK PRODUCTION SYSTEMS
South Island high country
South Island hill country
North Island hard hill country
North Island hill country
North Island intensive finishing systems
South Island finishing-breeding farms
South Island intensive finishing farms
South Island mixed cropping and finishing farms
Dairy farms
Ruminant sector demographics, products and exports
The sheep industry
Wool
The Beef Industry
The Deer industry
The Dairy industry
Socio-economic limitations of pastoral agriculture
Animal health and welfare
Parasites
Facial eczema
Johnes disease
Footrot
Scabby mouth
Liver fluke
Dairy herd diseases
Crown pastoral land act 
The resource management act (RMA) 


5. THE PASTURE RESOURCE
Development of the pasture resource
Pre settlement
Post settlement by Europeans
Post clearing “Bush sickness” after forest clearing
Development through improved soil fertility
Hill country development
Nitrogen use for pasture production
Irrigation
Pasture growth patterns
Temperature effects on production in summer moist regions
Production in summer dry regions
Seasonal variation in mean daily growth rates
Effects of topography
Altitude
Aspect and slope
Animal behaviour
Grass endophytes
Perennial ryegrass endophytes
Tall fescue endophytes
Pasture Species
Major species
Minor species
Species selection
Pastures for warm, summer moist regions
Cool, summer moist regions
Dryland pasture options
Lucerne
Alternative pasture grasses
Weeds
Weed control
Pest control
Disease
Pasture renewal programs
Maize in pasture rotations
Brassicas in pasture rotations
Pasture renewal programs in different farm systems

6. OPPORTUNITIES FOR IMPROVEMENT OF PASTURE RESOURCES
Improved on-farm management
Opportunities to overcome topographical limitations
Opportunities under dryland conditions
Nitrogen and legume use
Problems associated with intensification
Farm nutrient budgets
Adjustment of legislation
Social organization
Pasture plant improvement
High sugar grasses
Seed production in New Zealand
Better integration of forages into farming systems
Pasture rehabilitation
Weed control
Climate change
Summer-moist regions
Summer-dry regions

7. RESEARCH AND DEVELOPMENT ORGANIZATIONS AND PERSONNEL
AgResearch
DairyNZ Ltd, Hamilton
Lincoln University
Massey University

8. REFERENCES

9. CONTACTS


1. INTRODUCTION

Location and land area
New Zealand lies 2 162 km south east of Australia, between 34ºS and 47ºS (Figure 1a). It consists of three main islands, surrounded by the South Pacific Ocean and Tasman Sea (Figure 1b). The North and South islands are separated by Cook Strait (25-30 km). The smaller Stewart Island (1 746 km2) is located 20-30 km across Foveaux Strait to the south of the South Island. A range of smaller islands are also included as part of territorial New Zealand (C.I.A., 2009).

Figure 1a. Location of New Zealand
Figure 1b. Map of New Zealand
[Click to view full map]

The distance from the north of the North Island to the south of the South Island is about 1 600 km and the islands range in width from 20 to 450 km with 15 134 km of coast line. The area of the North Island is 113 729 km2, and the South Island is 151 215 km2. Total land area is about 27 million hectares (McKinnon, 1997).

The mountainous nature of the New Zealand landscape means only about one third of the land mass is flat to rolling country (slope 0-16°). The remaining two thirds is steep hill or mountainous (Hodgson et al., 2005). Over 75% of the country is at altitudes above 200 m and continued mountain building from movement of the underlying tectonic plates has resulted in a landscape dissected by fast flowing rivers, streams and lakes. Lake Taupo in the central North Island is the largest, covering 62 000 ha with a maximum depth of 163 m. Much of the North Island is rolling to steep hill country (slope >16°). In the South Island, mountain peaks in the Southern Alps feed water from glacial ice, snow melt and rainfall into fast flowing rivers which flow across alluvial floodplains.

Current population and distribution
New Zealand’s population (2009) is about 4.3 million (4 213 418 was the July 2009 estimate according to the World Factbook with a 2009 growth rate of 0.935%) which gives a population density of ~16 people/km2. However, >70% of the population live in the North Island so the population density is 28.6 people/km2 in the North Island compared with about 6.7 people/km2 in the South Island. In urban areas population density is 275-580 people/km2 whereas areas classified as rural have population densities which range from <1 to 14 people/km2. The largest city is Auckland which accounts for 31% of the total population. About 70% of the total population are classified as residents of urban areas (settlements with > 1 000 people) (Department of Statistics, 2009a).

Natural resources and the exclusive economic zone
New Zealand has limited quantities of mineral resources for commercial extraction, but larger quantities of minerals are located in unmined national parks. Consequently they contribute less to total export income and the domestic economy than agricultural products. Resources include natural gas, iron ore, sand, coal, timber, hydropower, gold and limestone (McKinnon, 1997).

The ~4.4 million km2 exclusive economic zone surrounding New Zealand is the seventh largest in the world (C.I.A., 2009) and 14 times greater than the land area. This zone includes subtropical and sub Antarctic waters, inter-tidal estuaries, mangroves and seabed trenches and contributes about 3% of the Gross Domestic Product (GDP).

Natural hazards
Earthquakes from tectonic movements, periodic volcanic activity and flooding can cause disruption to natural and managed ecosystems. Of these hazards, periodic flooding following heavy prolonged rainfall is the most common problem. This is compounded by the location of many cities and townships near rivers on floodplains or coastal settlements near river mouths. Agriculture can also be interrupted by flooding and occasional landslides on unstable hill slopes. In most cases, weather forecasts allow movement of humans and livestock ahead of rising waters but property damage and significant economic losses can occur.

Occasional heavy snow may result in periods when power and communications are cut to households but in most cases these are repaired within 1-2 days. Other major hazards include strong winds which can deplete topsoil of newly cultivated land and cause wind throw in forest plantations. Fire in grassland and regenerating or exotic plantation (predominantly Pinus radiata) forest can occur in summer dry conditions, particularly in eastern districts of the two main islands.

Farming area, ruminant numbers and main breeds
About 37% of the land mass is classified as pastoral and a further 0.2% as arable and horticultural land. In 2007, the pastoral land area supported almost 50 million ruminant livestock. Of these 77% were sheep, 11% were dairy cows, 9% beef cattle and 3% deer (see section 4).

The main sheep breeds include Romney, Corriedale, Coopworth, Perendale and Merino. Dual purpose and modern composite breeds are now most common as they allow income flexibility within farming systems. In dairy systems high milk and milk solids production is required and almost 80% of the national herd are Holstein-Friesian or Holstein-Friesian/Jersey crossbreeds. The main beef cattle breeds include Angus, Friesian, Angus/Hereford and Hereford. In the deer industry 85% of the national herd are red deer (Cervus elaphus) most of which are descended from feral animals captured in the 1980s. Information on the New Zealand ruminant industry and demographics is covered in Section 4.

Ruminant livestock enterprises in New Zealand are officially classified into nine farm classes. Each farm class differs in environment, soil fertility, pasture and animal production levels and the main farming operation. For example, the average South Island High Country farm had >80% steep land (>21°), a mean annual rainfall of about 740 mm/yr and an effective area of 10 660 ha with 81% of their livestock being sheep (Farm Class 1; Section 4). The average North Island finishing farm had an annual rainfall of 1190 mm/yr, 15% of the 270 ha of effective area is classified as steep land and 52% of livestock are sheep (Farm Class 5; Section 4). The average dairy farm had an effective area of 128 ha on flat to rolling land (0-15°), in environments with >1500 mm/yr of rainfall or where irrigation was available. Regionally, North Canterbury has the largest average herd size of 771 cows. There is a high level of integration among production systems with feed sources and livestock frequently moved between farm classes to overcome regional feed deficits and unseasonal weather events.

Exports
New Zealand has an open economy which is focused on the production of high quality agricultural products at low cost. Total agricultural exports account for almost half of New Zealand’s total exports (Department of Statistics, 2009a). Of this, ~30% is from meat and meat products and ~40% from dairy products (Table 1 ). Most exports are shipped, rather than air freighted offshore, due to transportation costs associated with the distance to the main export markets.

Table 1. Merchandised exports from New Zealand between 2002 and 2008 for the year ending 31 March
(Department of Statistics, 2009a; Ministry of Agriculture and Fisheries, 2009a).

 

Year

 

2002

2003

2004

2005

2006

2007

2008

 

NZ$ (millions)

Dairy products

7 834

6 308

6 057

6 266

6 807

8 405

10 478

Meat and meat products

4 526

4 341

4 309

4 796

4 541

4 953

4 565

Miscellaneous agricultural products

2 034

1 836

1 705

1 700

1 519

1 691

1 722

Wool

1 041

1 070

980

949

919

944

844

Live animals

157

141

170

264

200

157

177

Total agriculture

15 591

13 695

13 222

13 975

13 987

16 149

17 785

Horticultural products

1 961

1 960

1 969

2 349

2 276

2 533

2 802

Total agriculture and horticulture

17 552

15 655

15 190

16 324

16 264

18 682

20 588

Forestry products

3 612

3 717

3 125

3 255

3 164

3 562

2 900

Total agriculture and forestry exports

21 164

19 372

18 315

19 579

19 428

22 244

23 488

Other industry exports

10 362

9 796

9 189

10 135

10 276

11 250

13 169

Total New Zealand merchandised exports

31 527

29 168

27 504

29 714

29 704

33 494

36 657


Note: Values are New Zealand dollars free on board (fob) and exclude re-exports. Figures may not add or reconcile due to rounding.
Some figures have been suppressed to comply with Statistics New Zealand confidentiality rules after 2006.

Natural History

Native flora and fauna
Podocarps (Podocarpaceae.) and southern beech (Nothofagus spp.) are the dominant tree species in native forests. In the north of the North Island native forests were dominated by the giant kauri (Agathis australis) while climatic and physical differences in the environments led to southern beech dominance in the South Island. Tussock grassland dominates in the subalpine regions. Shrub vegetation includes matagouri (Discaria toumatou) and manuka (Leptospermum scoparium).

New Zealand has a high proportion of endemic species due to its isolation from neighbouring land masses. In recent time (in geological terms), the islands had no native terrestrial mammals except for two species of rarely seen bats. Native fauna is dominated by insects and birds (McKinnon, 1997). A lack of mammalian predation meant that many native species were poorly adapted to attack by introduced predators. For example, many native bird species are vulnerable because they are flightless and others nest on the ground. The kiwi (Apteryx spp.) is a flightless, leaf-litter forager that has become one of the national symbols of New Zealand.

Maori colonisation
It has been estimated that the Polynesian Maori people arrived in New Zealand about 800 years ago after travelling from the tropical islands in the South Pacific (McKinnon, 1997). Once the easily exploited large flightless birds and sea mammals (seal species) became scarce Maori became more reliant on their horticultural skills and evolved methods for growing sub tropical crops such as kumara (sweet potato, Ipomoea batatas) and taro (Colocasia esculenta) in the warm temperate climate of the coastal North Island.

Post-human species introductions
In combination with human activity, introduced predators have resulted in the extinction of up to 50% of native bird species. The first human induced extinction wave was initiated after Polynesian people arrived in the 13th Century A.D. with dogs (used for hunting and food) and the small Polynesian rat (Rattus exulans). The rat fed on the eggs and young chicks of smaller ground nesting birds. Polynesian (Maori) settlement resulted in many of the larger bird species, such as Moa (Dinornis spp.), being hunted for food. Initially, there were 10 species of Moa, some of which reached >2.5 m in height and over 270 kg in weight. These became extinct about 700 years ago. Consequently, with the loss of its primary food source the giant predatory Haast Eagle (Harpagornis moorei), (9-15 kg weight) became extinct shortly after the Moa.

After the Englishman Captain James Cook “discovered” and mapped New Zealand in 1769, European settlers introduced a range of species. These included rabbits (Oryctolagus cuniculus) followed by predatory mammalian species such as stoats (Mustela erminea) to try to control the exploding rabbit population. Native species were vulnerable to these predators and unable to adapt. This has resulted in extinctions and placed numerous species in an endangered category. With the development of European agriculture many species of crop and associated weed species were introduced during the late eighteenth century and through the nineteenth century. This has also reduced the habitat available for native species.

Conservation and biosecurity
Since human settlement, New Zealand’s land cover has undergone dramatic alteration. Fires for hunting Moa, shifting cultivation (Maori) and creating farmland (European settlers) have reduced the native forest particularly on lowland sites with flat to rolling aspect. These areas are now predominantly used for pastoral agriculture, horticulture, cropping and urbanisation. As an island nation New Zealand now has some of the strictest biosecurity and import regulation measures in the world to protect its exports of agricultural, forestry and fishery products.

Figure 2. Change in land cover from pre-human (left) to current (2002) (Ministry for the Environment, 2007).
[Click to view full images]

These biosecurity measures reflect the isolation and therefore low pest and disease levels compared with other countries. From an agricultural perspective, the increase in movements of people and goods between countries has highlighted the vulnerability of primary industries to accidental introductions of pests/diseases from other countries. A recent example is the discovery of the Varroa bee mite (Varroa destructor). This initially infected bee hives in the north of the North Island (Stevenson et al., 2005) but has now reached the South Island. This directly affects the honey industry, and the pollination of fruit, vegetables and herbage seeds. New Zealand has remained free of foot and mouth disease due to vigilance in hygiene and inspection associated with meat or livestock imports.

Tourism
New Zealand has spectacular scenery including national parks, geothermal areas, mountains, fiords, tussock grasslands, forests and native birds. Adventure activities include bungy jumping, jet boating, skiing, canyoning, caving and mountain biking [www.newzealand.com]. Wildlife encounters include whale watching, swimming with dolphins, seals and penguins.

Figure 3. Department of Conservation land, which includes National Parks, and other protected land areas in New Zealand (Ministry for the Environment, 2007).
[Click to view full image]

European colonisation and agricultural development

European colonisation
New Zealand was discovered twice by Europeans and lays claim to being the “youngest country” on earth as no other large land masses were subsequently discovered [Further information can be found at www.nzhistory.net.nz] . The Dutchman, Abel Tasman, mapped part of the coastline in 1642/43, but the country was not colonised by Europeans until after it was mapped more accurately by James Cook during several voyages between 1769 and 1779 (McKinnon, 1997). Whaling and sealing industries established soon after Cook’s visits. The main period of organised European colonisation began in 1840s following the signing of the Treaty of Waitangi between Maori and the British Crown. By 1855 the first elections for the House of Representatives were held and in 1865 the capital was moved from Auckland to Wellington. Initially, settlers purchased land from Maori. Later military conflicts (Land Wars) led to the confiscation of land under the New Zealand Settlements Act of 1863 by the colonial government and European settlers. Settlement of Treaty claims by regional iwi (tribes) against the government resulting from confiscation of lands by the Crown is on-going.

Agricultural development
New Zealand’s agriculture industry has had a large and defining effect on the environment, economy and perceptions of national identity. Agricultural expansion happened rapidly between 1865 and 1915 (see section 5) as native forest was felled, burnt and introduced pasture species broadcast on cleared land. The first refrigerated exports from New Zealand to Great Britain occurred in 1882. This created new markets for meat and dairy products and led to an increase in intensive pastoral agriculture in contrast to extensive wool production.

Agricultural subsidies and regulation dominated the New Zealand economy from 1935 to 1984. Measures included subsidies for irrigation, water supply, fertilizer and lime transport, fertilizer purchase and aerial spreading costs, labour support for fencing and land development and associated loans, grants and cheap credit.

Deregulation of the agricultural industry in the mid 1980s resulted in the removal of all farm subsidies (Sandrey and Reynolds, 1990). This created many financial difficulties for farmers who had become reliant on government intervention to protect their livelihoods. The deregulation was instigated to encourage more efficient use of resources in the necessary drive to produce products which were competitive on world markets. This has been successful in the longer term, but initially those farmers who were unable to adapt, or who were burdened with large debt, left the industry. Since the 1990s agriculture has been driven by market demand. Farmers have become more flexible and rapidly change land use to adapt to changes in market and economic signals. A recent example of this responsiveness is the rapid conversion of sheep and beef farms to dairying (see section 4).


2. SOILS AND TOPOGRAPHY

Major Topographic Features
New Zealand was once part of the Gondwana supercontinent. After the “Rangitata” land mass broke away, ~80 million years ago, it drifted eastwards on the Pacific tectonic plate. The majority of this land mass is now submerged, but parts of New Zealand may have managed to (periodically) stay above water. Originally flora and fauna were similar to that found on the supercontinent. However, by the time marsupials evolved, ~70 million years ago, New Zealand was surrounded by ocean. Consequently, narrow seas separated the land masses and seed and birds crossed between them but movement of larger land based animals was restricted (McKinnon, 1997).

New Zealand lies on the rather unstable boundary above the Indo-Australian and Pacific Tectonic Plates. The Alpine Fault runs the length of the South Island, below the Southern Alps, and continues up the east coast of the North Island. The Southern Alps, which geographically and climatically separates the east and west coasts of the South Island, were formed by the uplifting of the continental crust of the Pacific Plate by the underlying Indo-Australian Plate (McKinnon, 1997). Today, the Southern Alps continue to increase in height by 0.8-10 mm/ yr (Tippett and Kamp, 1995). Mt Cook, also known by its Maori name of “Aoraki”, is New Zealand’s highest mountain and rises to 3 754 m a.s.l. A further 18 mountains are >3 000 m a.s.l. Given the position of the country in relation to the underlying tectonic plates, earthquakes are common (most are minor and not felt by the majority of people) but a few have caused significant damage. Below the North Island, pressure between the two plates causes formation of magma (80-100 km deep), which rises to the surface forming a line of, occasionally active, volcanoes running in a north east direction from Mt Ruapehu (2 797 m a.s.l.) in the central North Island to White Island in the Bay of Plenty. Consequently these areas are dominated by geothermal activity which is the basis of tourism in Rotorua and has been harnessed for geothermal power generation especially in the central North Island.

Over 75% of New Zealand’s land mass is >200 m a.s.l. and continued mountain building from movement of the underlying tectonic plates has resulted in a landscape dissected by fast flowing rivers and streams (see Figure 4). These feed numerous lakes. The largest is Lake Taupo in the Central North Island which covers 62 000 ha and has a maximum depth of 163 m. In the South Island, glaciers of varying size, carry away water from snow and ice melt from the mountain peaks in the Southern Alps. These glaciers are currently (2009) in a cycle of retreat. Much of the North Island is classified as rolling to steep hill country. Given the mountainous nature of the landscape it is important to note that only about 33% of New Zealand’s land area is classified as flat to rolling country. The remaining two thirds is steep hill or mountainous (Hodgson et al., 2005).

Figure 4. Topographical map of New Zealand including towns and cities.
[Click to view full image]

Soils
Pedologically, New Zealand has a young landscape formed from periods of mountain building, glaciation, volcanic activity and weathering by wind and water with no prolonged periods of landscape stability (White, 1999). However, with the exception of recent volcanic material, the majority of current landscapes were formed from reworked volcanic, sedimentary and metamorphic material from previous landscapes (O'Connor, 1984). Most soils have low to moderate native soil fertility, and are slightly acidic (pH 4.5-5.5) with low nitrogen (N), phosphorus (P) and sulphur (S) and micronutrients which include boron (B), cobalt (Co), copper (Cu), selenium (Se), iodine (I) and Molybdenum (Mo) (Kemp et al., 1999). Distance from the sea coast in association with topography and high rainfall reduces sodium (Na), S, B and I availability in inland regions.

Phosphate and sulphur based fertilizers with Mo and/or lime have been widely adopted in all pastoral ecosystems (flat, rolling, hill, high country), to encourage biological N fixation from pastoral legumes.

The interaction of climate, topography, parent materials and time has resulted in many different soil types (>100) with varying soil properties, native nutrient levels and soil depths to parent material (McLaren and Cameron, 1996). An example of one of the soils found on a Canterbury floodplain, and which is currently used for pastoral agriculture, is shown in Figure 5. On these floodplains, soil depth to gravel can vary from <0.5 m to >3 m and this changes greatly over small (5.0 m) distances. This reflects the underlying effect of previous river channels and river banks which have dissected the plains. The majority of pastoral topsoils are high (3-10%) in organic matter and this generally increases with the duration under pasture.

Figure 5. Soil pit showing depth to alluvial gravels under a lucerne (alfalfa; Medicago sativa) stand in the Lees Valley (400-500 m ), Canterbury, New Zealand. These soils, located on the valley bottom, are classified as Recent soils (see below).

As shown by Figure 4, New Zealand is a mountainous country with the majority of its limited flat land formed from alluvial floodplains and glacial outwash fans. Its pastoral area can be divided into three categories, each of which account for about one third of the total pastoral area (Bryant and Sheath, 1987). These three grassland types are: “High country” which refers to the 4.5 M ha of pastures on land with slopes >21°, a further 5.0 M ha of “Hill country” pastures are on land with slopes of 16-20° and “Flat to rolling land” grassland (0-15° slopes) account for the remaining 4.5 M ha. More than half of all improved pastures are on easily cultivatable flat to rolling land.

Soil classification
The New Zealand Soil Classification system was introduced in 1992 and groups soils based on the degree of similarity between observed/measured properties (Hewitt, 1992; McLaren and Cameron, 1996). The main soil properties are summarised in Table 2 and their geographic distribution is shown in Figure 6.

Table 2. Major soil orders and their main diagnostic features for classification under the New Zealand soil classification system (Hewitt, 1992; McLaren and Cameron, 1996).

Soil Order

Main Diagnostic Feature

Allophanic

Soils dominated by allophane

Anthropic

Soils constructed or drastically disturbed by human activity

Brown

Aerobic soils with brown colours due to iron oxide coatings

Gley

Waterlogged, anaerobic soils with Br and/or Cr horizons

Granular

Clayey soils derived by strong weathering of ancient volcanic rocks. Usually, dominated by well-developed nutty structure throughout A and B horizons.

Melanic

Soils with dark A horizons and high base status. Subsoil contains lime or have well developed structure.

Organic

Soils consisting predominantly of organic material

Oxidic

Clayey soils dominated by oxidic horizons (Bo) containing crystalline aluminium and iron oxides.

Pallic

Soils with pale coloured subsoils with high slaking potential and high density (often in the form of a fragipan, Bx horizon)

Podzols

Strongly leached acid soils with E horizons underlain by accumulations of aluminium/iron/humus (Bs, Bh, Bsh or Bfm horizons).

Pumice

Soils dominated by pumice or pumice sand with a high content of natural glass.

Raw

Very young soils without distinct topsoil

Recent

Weakly developed soils showing minimal profile development but with distinct topsoil.

Semiarid

Dry, weakly weathered soils with high base status. Accumulations of lime and salts common in subsoils (Bk or Bky (sic was Bk) horizons).

Ultic

Strongly weathered soils with clay enriched subsoils (Bt horizons).

In the North Island the three main soils are Pumice, Allophanic (with a volcanic parent material) and Brown soils. In contrast, the west coast of the South Island is dominated by Podzols (high rainfall environments with high organic matter inputs) with Brown and Pallic soils on the east coast. In the Canterbury region, formed on an alluvial floodplain, stony Brown soils and Raw soils dominate, indicating the young age of the Plains. In Central Otago Semiarid soils occur in environments with mean annual rainfall <500 mm/year. Gravel scree and Raw soils dominate the steep upper slopes of the dividing Southern Alps. These have low native fertility as they are geologically young, and have many intergrade soils.

Sparling and Shipper (2004) reported differences in soil quality as part of the 500 Soils Project (Table 3). Soil samples (0-0.1 m) were taken from 511 sites of differing land use which represented 98% of the New Zealand land area. They analysed soil pH, N, P and C content and macroporosity. Overall, it was shown that grazed pastures had higher mean total N content (>4.6%) than all other land uses (<3.5%). Mean soil pH was lowest under native and exotic forests (<5.4) and highest in cropping systems (>6.1).

Table 3. Summary of mean soil pH (H2O), mineralisable nitrogen (N, µg/m3), total N (mg/cm3), total carbon (C, mg/cm3), Olsen P (µg/m3) and macroporosity (%) of soil samples taken from 511 sites throughout New Zealand and grouped by land use. (n) is the number of samples which contribute to the mean value in each land use category. “Dry stock pasture” includes sheep, beef and deer farming and “tussock grasslands’ were mainly grazed by sheep and beef (Sparling and Shipper, 2004).

Soil property

Arable cropping

Mixed cropping

Dry stock pasture

Dairy pasture

Tussock grasslands

Exotic forestry

Native forests

(n)

44

17

142

127

20

67

58

pH

6.2

6.2

5.8

5.7

5.6

5.4

5.4

Mineralisable N

56

70

128

160

88

63

100

Total N

2.3

3.1

4.3

5.9

2.6

3.0

3.5

Total C

41

38

51

67

38

46

57

Olsen P

49

44

19

44

16

10

11

Macroporosity

14.7

9.3

13.3

10.1

15.6

25.6

9.3

Soil erosion
Natural soil erosion occurs in the more fragile ecosystems, such as the steep hill country in the North Island. Erosion has always shaped the New Zealand landscape because 30% of the land area has slopes >25°. In some cases this process has been accelerated by the removal of native forest and replacement by low producing pasture. Consequently, when high impact rain events occur they saturate the soil on steep hill slopes which can cause mass soil movement (Ministry for the Environment, 2007). The effects are generally more common on the east coast of the North Island than in other regions. Tunnel gully erosion occurs predominantly on summer dry, low productivity grassland hill slopes of the eastern South Island. Soils in these erosion prone areas tend to have subsoils formed from poorly structured loess and contain fragipans which are dense. Subsurface water movement erodes the soil above the pan which eventually results in gully formation (McLaren and Cameron, 1996).

Figure 6. Geographic distribution of the dominant soil groups in New Zealand. For the purposes of this figure the Brown soil order has been divided into two sub-orders (Brown soils and Brown soils – stony). In the North Island 14 of the 15 soil orders occur. In the South Island 12 of the 15 soil orders occur (Adapted from Molloy, 1998 in Ministry for the Environment, 2007).

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