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Soils and regional land use

by  Allan Gillingham

Underlying New Zealand’s varied landscape is a mosaic of soils. The type of soil, along with temperature and rainfall, determine how the land will be used for farming. But even inhospitable land can be developed with fertiliser to make it suitable for raising animals and crops.


Overview

How land is used commercially depends on its topography, soil properties and the climate (mainly temperature and rainfall).

Land types

Almost half of New Zealand’s land is farmed commercially – over 40% of the total land area is pasture and arable cropping land, about 7% is exotic forest, and less than 2% is orchard or market garden. The remainder is indigenous forest and shrubland (33%), tussock grassland (14%), urban area (1%), alpine zone, low-lying wetland or coastal sand.

Topography and use

Flat land is used for growing crops, feeding young stock for sale, and most dairy farming. Most flat land in New Zealand is in the South Island, especially on the Canterbury and Southland plains, and in Central Otago.

Rolling and moderately steep slopes are used for sheep, beef and deer farming, and forestry. Most forestry is in the North Island. Hill country is farmed in all regions of the North Island, and in all except the West Coast of the South Island. Farmed high-country tussock grasslands extend mainly from Marlborough to Southland.

Climate

Temperature

The mean annual temperature decreases from north to south – for example, in Auckland it is 15.3°C and in Dunedin it is 10.8°C. Temperature also decreases by about 0.5°C with every 100-metre increase in altitude.

Minimum winter temperatures affect the flowering and seeding patterns of some plants. If the temperature is less than 5°C, plant growth will stop. However, it is the number of frost-free days in a year that dictates where frost-sensitive plants can be grown.

Rainfall

Rainfall varies even more markedly across New Zealand – from more than 5,000 millimetres annually in Fiordland to less than 400 millimetres in Central Otago. Plant growth depends on available moisture in the soil, which is the difference between rainfall and evaporation in a given period. Moisture deficits occur when more water evaporates from the soil than is replaced by rain, usually in late spring and early autumn. The sum of these deficits annually across the country ranges from slight (1–20 millimetres) to high (200–300 millimetres). When soil moisture gets too low, plants stop growing, and in drought conditions they die.

Droughts are common on the east coasts of New Zealand, but not on the west. In all regions, the soil on steep slopes, especially north-facing aspects, is drier than soil on nearby flat land.

Soil fertility and growth

The natural fertility of soils varies around New Zealand, but fertilisers are spread on all soils where plants and animals are raised commercially. Fertilisers balance nutrients in the soil for plant and animal growth. Plant and animal tissue is made up of carbon, hydrogen and oxygen, plus other mineral elements. The main elements are nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and sodium. Others needed in tiny amounts are the trace elements boron, iron, manganese, copper, zinc, molybdenum, chlorine, cobalt, iodine and selenium.

Fertilisers

All New Zealand soils, particularly those in the North Island, are deficient in phosphorus, so phosphate fertiliser is applied to all pasture and crop land.

Nitrogen fixing

White clover is the most important and widespread legume in New Zealand pastures, and is the basis of the country’s relatively low-cost pastoral agricultural systems. Soil bacteria attached to legume plant roots convert or ‘fix’ nitrogen in the atmosphere to a form that can be used by other plants – including crops.

Nitrogen is added to supplement the natural process of nitrogen fixation – where pasture legumes convert nitrogen in the atmosphere to a form in the soil that can be used by other plants. The use of nitrogen fertiliser has increased because of the rapid expansion of dairy farming, especially in the South Island. Dairying is more intensive than sheep and beef farming, and the pasture needs to grow faster. Higher rates of other nutrients are also needed.

Soil acidity

Plant growth is affected by soil acidity, which is measured on the pH scale. Soil with a pH of 4.8–5.2 is strongly acidic and likely to restrict plant growth, whereas a pH of 6.6–7.5 is neutral. The optimum pH for pasture growth is 5.8–6. If soil pH needs to be raised (made more alkaline), lime is applied. Lime is quarried and finely ground at several sites in New Zealand.


Northland

Topography

Much of Northland is undulating to moderately steep hill country that has been weathered by the subtropical climate over a long period of time. As a result, most of the soils contain a lot of clay and are called clays or clay loams.

Climate

Northland has a subtropical climate, with minimum winter temperatures of 6–9°C. Grasses such as paspalum and kikuyu grow in pastures. Paspalum is found further south, but kikuyu cannot thrive where there are winter frosts.

Soils and land use

On the flatter areas, which were originally covered in kauri-dominated forest, so-called gumland soils developed. These were mined for kauri gum in the late 19th and early 20th centuries. Superphosphate is needed on gumland soils used for forestry, and potassium fertiliser is used on podzolised sands (areas leached of nutrients by weathering and acid tree litter). Forest grown near coastal sand dunes also need nitrogen fertiliser, or associated plantings of lupins – which ‘fix’ nitrogen in the soil so it can be used by the trees.

Gley podzol soils are used for sheep and beef farming, and dairying, but need lots of initial fertilisation. Derived from sedimentary parent rocks, gley podzols have brown clay topsoils, and are wet in winter and spring. They cannot support large numbers of cattle at those times, unless the soil is well drained.

The other Northland soils are mostly a mix of brown soils, free-draining soils from basalt, and poorly drained hill and steepland soils from old andesitic volcanic action. The best free-draining (oxidic) soils, from more recent basaltic volcanism, are used for dairying and a range of horticultural crops.

All Northland’s soils are acidic and low in natural phosphorus and sulfur, so lime and superphosphate fertiliser (9% phosphorus, 11% sulfur) are needed for pasture growth. Other nutrients such as potassium, molybdenum and copper may also be required, especially after the land has been farmed for some time.


South Auckland, Waikato, Coromandel, Bay of Plenty

South Auckland and Waikato

Topography and climate

The gently undulating topography of most of South Auckland and the central Waikato basin contains some of the most productive farmland in New Zealand. The minimum winter temperatures are 3–6°C, with warmest temperatures further inland. The annual water deficit is low, although summer droughts can occur.

Soils and land use

The free-draining loam soils have developed from volcanic ashes of varying ages, and are easily cultivated. They are good for crops, horticulture or intensive dairying. In the south of the region, where there is more rain, the soil contains a fine clay called allophane. This absorbs phosphate and sulfate, so extra fertiliser is often needed to establish good legume-based pastures.

In the Hamilton basin and towards Matamata, the Waikato River has sorted and deposited a mixture of ash material to form complexes of poorer drained gley soils and free-draining, sandy and gravelly soils prone to summer drying.

In the Hauraki Plains and around Hamilton there are large areas of peaty loam and peat soils, formed as a result of poor drainage. Most have been drained for dairying. All need a lot of added lime, which is ploughed in for best results. Heavy applications of phosphorus, potassium and sulfur are also initially needed, and boron must be added for brassica crops (such as cabbages and broccoli). Pastures and the animals who eat them may be copper deficient, and selenium deficiency is common in young stock.

The steeper hill country to the west is a mosaic of ash-derived soils on rolling and moderate slopes, and mudstone-derived soils on steep slopes where the ash has been washed off. Pastures on the steep slopes need less phosphorus and sulfur fertiliser than those on the ash soils, and respond to lime. Most pastures are used for sheep and beef farming. Shallow hill soils may need phosphorus fertiliser for exotic forestry production.

Steep slopes impose greater moisture stress on pastures because of the greater opportunity for runoff of rain water. On north-facing aspects there is greater evapo-transpiration of soil moisture than on flat land. As a result, pastures on hill slopes usually show browning earlier in summer than associated flats.

Coromandel and Bay of Plenty

This region is well known for its beaches, and is the main kiwifruit and avocado growing area in New Zealand. However, horticulture occupies only about 1% of the land area. About 90% of the area is covered by indigenous forest, exotic plantations or pasture. Dairying and horticulture are still expanding on the flat and gently rolling land at the expense of sheep and beef farming. The Coromandel ranges once grew kauri forests.

What’s in superphosphate?

About 2 million tonnes of superphosphate fertiliser are applied to farms in New Zealand each year. Superphosphate is made by adding sulfuric acid to rock phosphate. Superphosphate contains both sulfur from the sulfuric acid, and phosphorus from the rock. Other nutrients can be easily added where necessary.

Minimum temperatures in winter are higher than in central Waikato, and the annual water deficit is only slight or near zero.

The soils are mainly loams derived from volcanic ash, crumble easily and are free draining. They strongly retain phosphate and sulfate, so relatively large amounts of superphosphate fertiliser are needed. They are deficient in potassium and increasingly in cobalt. Lime is eventually required to counter the effect of soil acidification, which occurs naturally under grazed grass/legume pastures.


Central and western North Island

Volcanic Plateau

This region, shaped by eruptions 300,000 to 750,000 years ago, is dominated by Lake Taupō, the largest lake in New Zealand. The volcanoes of the Tongariro National Park lie to the south and the Rotorua lakes are in the north.

Minimum winter temperatures are generally 0–3°C, and the annual water deficit is near zero.

Today’s soils were formed from volcanic pumice showers from the Taupō and Kaharoa eruptions, which occurred in the last 4,000 years. Finer pumice also extends as far east as Gisborne, and into the Waikato and Bay of Plenty in the north. Pumice soils are used predominantly for sheep and beef farming, although dairying has expanded in recent years.

Farming this land was impossible until the early 1900s because all ruminant stock suffered from bush sickness, later diagnosed as cobalt deficiency. Before this problem was solved, about 400,000 hectares were planted in exotic forest (Pinus radiata) as the only viable land use. Large areas are now being converted from forestry to pasture for dairying.

Pumice soils usually have a thin, well-developed organic topsoil over a sandy subsoil. Initially, plenty of sulfur-fortified superphosphate is needed to establish pasture. Potassium, magnesium, cobalt and copper, and in some areas selenium, are also usually necessary for stock. Boron deficiency in lucerne and brassica crops is widespread.

Where the soils dry out in summer, the clover content of pasture is usually low and deficient in nitrogen the following winter and spring. Phosphorus, magnesium, boron and possibly nitrogen and potassium are needed for exotic forestry, especially where the soil is coarse and the topsoil shallow.

Taranaki and the King Country

Like the Waikato, Taranaki is widely known as a dairying province. Minimum winter temperatures are mild (3–6°C), especially nearer the coast, and the annual water deficit is near zero.

The rolling landscapes in the western half are dominated by soils made of andesitic ash from Mt Taranaki. In the east, these soils are very crumbly with good drainage, but to the west of the mountain the ring plain has stony soils with impeded drainage. As with other ash-derived soils, these also need phosphorus, sulfur and potassium fertilisers to establish and maintain pasture. Lime is not required because of the naturally suitable soil pH (pH 5.6–6.0).

The land in the east of Taranaki and in the King Country is a mosaic of easier ash-covered slopes and steeply dissected mudstone-, siltstone- and sandstone-derived soils with lower fertiliser requirements. Some phosphorus may be needed for exotic forestry. These soils are mainly used for sheep and beef farming, but erode easily. The pastures will quickly revert to fern and scrub if subdivision and grazing intensity is inadequate.


Lower North Island

East Coast and Manawatū

Minimum winter temperatures are mild (3–6°C).The annual water deficit is generally low, but moderate on Manawatū’s sandy soils, the flats of Gisborne, and the flats and hill country of Hawke’s Bay and the Wairarapa.

Whereas most soils in the top half of the North Island are dominated by volcanic ash, large areas of the Hawke’s Bay, Wairarapa, Manawatū and Wellington regions are formed from mudstone, sandstone, greywacke or limestone. These soils are mainly silt loams, and in the east where there is less rainfall, and on flat or undulating land, there may be compacted subsoils. Erosion is noticeable on many steep hill-country slopes.

The lower North Island is split by the Tararua and Ruahine ranges. In the west, the land is dominated by moderate to steep hill country, which is used for sheep and beef farming. There are also dissected loess-covered ancient terraces and alluvial flood plains, used for dairying and cropping. In the east, forestry and sheep and beef farming occupy the highly erodible mudstones of Gisborne–East Cape as well as the drier siltstone hills and steeplands of Hawke’s Bay and the Wairarapa.

The Gimblett Gravels

The Gimblett Gravels is a large area of stony, shallow soil in central Hawke’s Bay. It has little organic matter and is free-draining, holding very little water. It produces little pasture because every summer it suffers drought. But the area has proven excellent for viticulture, and a range of deeper-rooting grape varieties, especially Merlot, are grown very successfully.

Orchards on the Heretaunga plains are on some of the better Hawke’s Bay alluvial soils. Grape vines have been planted on the stony soils of Hawke’s Bay and the Wairarapa, which previously supported only small numbers of sheep. The growth of viticulture and horticulture has increased the demand for irrigation water. Irrigation has made dairying possible away from the wetter fringes of the mountain ranges.

Much of the west coast of the Manawatū has sandy soils, deposited as the shoreline advanced and retreated. A large part of this area has been planted in exotic forest. On the more recent sands, nitrogen and phosphorus fertilisers may be needed for tree growth. The oldest, firmer sands have been cultivated, fertilised and used for dairying, and nearer Wellington, for vegetable growing.

Slips

Most erosion on North Island hill country is in the form of slips – the mass movement of topsoil down slopes. A slip may disturb fences or cover tracks, and so disrupt farm management and pasture production. Even when over-sown with grass seed and fertilised, slip areas virtually never recover their original productive capacity – lost topsoil takes decades to even partially redevelop.

All soils respond to phosphorus and sulfur fertiliser to varying extents, with the drier hills in Hawke’s Bay and the Wairarapa needing less than in higher rainfall zones or on flat land. Where soil pH levels are low, lime can be beneficial.


Northern and western South Island

Marlborough

Low annual rainfall, regular summer droughts (high to very high annual water deficits) and brown pastures are characteristic of Marlborough. Although minimum winter temperatures are cool (0–3°C), stone (summer) fruit and horticultural crops ripen well. Large areas of gravelly terrace soils have been planted in grapes, which are suited to the climate and are more productive than pastures.

Marlborough’s hill soils are similar to those in the Wairarapa and Canterbury, but in the dry climate they can develop underground ‘tunnel gullies’ that eventually collapse and erode. The loess-covered soils of the Marlborough Sounds receive more rainfall and are more productive, especially on south-facing slopes. Under original forest cover, and where rainfall exceeds 2,000 millimetres, some soils have become acidic and have low fertility.

Molesworth Station

New Zealand’s largest property is Molesworth Station, in the upper Awatere valley, Marlborough. In the mid-1900s it became over-grazed by sheep and rabbits, and was subsequently taken over by the government. By controlling the rabbits, removing the sheep and replacing them with cattle, the vegetation recovered and the property’s productivity improved. Molesworth is now run by the Department of Conservation, and is open to tourists in summer.

Sulfur-fortified superphosphate with added molybdenum is usually needed to establish pasture. However, large areas of the region, including what was once farmland, are protected nature reserves or have been planted in exotic forest.

Nelson and Golden Bay

This region has cool minimum temperatures of 0–3ºC in winter, and a low-to-moderate annual water deficit. Nelson is known for pip and stone (summer) fruit, berries, hops and kiwifruit, and its sunny climate. Horticulture is concentrated and expanding on the fertile Waimea and Motueka flats and terraces.

The very old Moutere gravels to the south and west form the basis of 100,000 hectares of hill-country soils. Molybdic superphosphate plus potash, as well as lime, copper and cobalt are necessary to establish pastures, which are mainly used for sheep and beef production. Large areas of these gravels are planted in exotic forest, especially in southern Nelson, where nitrogen, phosphorus and boron fertilisers are generally required. There are also significant areas of native forest.

Nearer the coast, on easier topography, the more weathered gravels support Nelson’s apple and pear orchards. These need magnesium and boron fertilisers. Golden Bay, on the western side of Tākaka Hill, has fertile alluvial flats, 90% of which is pasture and increasingly being developed for dairying.

The West Coast

The West Coast is a mosaic of alluvial soils on flat river plains, with native forest growing on river valley slopes. The area’s plentiful rain contributes to an annual water surplus. Minimum temperatures in winter are cool (0–3°C). A large proportion of New Zealand’s indigenous forest is on the West Coast.

Soils on the flats are either recently formed from flood gravels and silts, or are very old pakihi soils (a Māori word that means open country). Pakihi soils have developed perched water tables as a result of very compacted, impermeable subsoils or an iron ‘pan’. The recent soils can be cultivated relatively easily with some drainage and fertiliser, but the pakihi podzols need special attention. One approach has been to develop hump-and-hollow land, where a flat area is contoured to improve drainage. Exotic forestry uses this method, with trees planted on the humps. Dairy farmers have also made remarkable gains by ‘flipping’ their poorly drained soils. This involves the use of diggers to break open the impervious pans and mix the peaty topsoil with the sandy subsoil. By flipping and hump-and-hollow contouring, then fertilising and re-sowing pasture, cow stocking rates can be doubled and the renovation costs paid back within two years.

Establishing pasture in the West Coast requires lime and lots of superphosphate. Copper, magnesium, molybdenum, cobalt and potassium may also be needed. Dairying has expanded and intensified rapidly on all soils in recent years. Nitrogen and phosphorus, as well as some potassium fertilisers are needed for forest grown on pakihi soils. Forests on dredge tailings usually also need boron.


Eastern and southern South Island

Canterbury

The Canterbury Plains are formed by extensive terraces and large alluvial fans near the main rivers, with a backdrop of downlands and hills approaching the Southern Alps. As you move east from the mountains the annual water deficit increases from low to high, and minimum winter temperatures increase from cold to cool (-3–3°C). The older segments of the upper plains have a thicker covering of loess than the younger alluvial plains. Large areas of the lower plains and some of the stonier soils on the upper plains were once planted in wheat, barley, oats, brassicas and pasture. These areas have been converted to dairy farms with the aid of large irrigation units. Irrigation is more extensive in Canterbury than in any other region.

The undulating, loess-derived downlands are used for semi-intensive sheep and beef farming, and cropping. Tussock grasslands, with higher rainfall, are on the slopes and flats of intermontane basins along the eastern ridge of the Southern Alps. These have shallow, stony and very friable soils. On the flat areas, the soil breaks apart and becomes ‘fluffy’ if cultivated. A large area in the Mackenzie Country has such soil, which, with the aid of irrigation, can be used for dairying.

Irrigation

In the early 20th century the downlands irrigation scheme was set up to divert water from the Rangitātā River into large canals that crossed Canterbury’s upper plains. The water was accessed by farmers, who fed it into border-dyke channels in their paddocks. These were wide parallel strips with a low border of earth on each side, on a slight slope, which channelled the water slowly across the pasture. Today, land is irrigated by large sprinklers tapping underground water.

The main nutrients needed in Canterbury are phosphorus, sulfur and molybdenum. Deep, moist soils lie on easy slopes, and there are stony or eroded soils on steep slopes, where pasture growth is limited by dryness in summer and cold in winter and early spring. Oversowing the hills with inoculated clover seed, together with the application of molybdenum- and sulfur-fortified superphosphate, has been an inexpensive way to develop large areas of tussockland into pasture in all eastern areas of the South Island.

Central and North Otago

Central Otago is the driest region in New Zealand, with an annual rainfall of some 400 millimetres. Although it has fertile soils, pasture and crop growth is limited by the high (200–300-millimetre) annual water deficit. Minimum winter temperatures are very cold (less than 2.5°C). Many apricot and cherry orchards have been converted to vineyards. To the east, rainfall is higher and more uniformly distributed.

The predominantly rolling hill country in North Otago can have good pastures once the phosphorus, sulfur, molybdenum, and in some cases potassium, requirements are met. Where irrigation is available, large dairy farms are being established on flat or easy-sloping soils.

South Otago and Southland

In these regions the annual water deficit ranges from zero to low and the minimum winter temperatures from cold (-3–0°C) in the north, to cool (0–3°C) nearer the southern coast. The Southland Plains have over the last 10 years undergone a transformation in land use from predominantly sheep and beef farming and cropping, to dairying. The moist, brown soils generally require drainage, and are high producing under additional lime, phosphate, and sulfur fertiliser inputs. Pasture production levels are as high as in the Waikato. Molybdenum is also important on the loess-covered downland hill soils in the north and east, where sheep and beef cattle farming predominates.


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How to cite this page: Allan Gillingham, 'Soils and regional land use', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/soils-and-regional-land-use/print (accessed 21 August 2019)

Story by Allan Gillingham, published 24 Nov 2008