Glossary of Terms/Information
- New Zealand Land Resource Inventory (NZLRI)
- Land Use Capability (LUC)
- LUC Subclasses (LUC Class and Dominant Limitation of the Map Unit)
- New Zealand Land Cover Database (LCDB) Classes
- General Soils Overview
- Landform and Site Characteristics
- Hydrological Characterisitcs
- Climatic Attributes
The Land Use Capability (LUC) system of mapping and land classification can be used to map and classify land at any scale. It has therefore been used to map and classify all land in New Zealand at 1:50 000 as part of the NZLRI, and many farm plans and catchment plans in most NZ regions at scales greater than 1:25 000. The classification and assessment is based on key physical resource information and knowledge of landform, rock type, soils, slope, erosion characteristics, vegetation, climate (e.g., rainfall, wind exposure), elevation or altitude, and land-use history. The LUC assessment for each parcel of land mapped (at a given scale) provides information on the land’s capacity for sustained productive use, physical limitations, and management requirements for soil conservation. LUC is used with the New Zealand Land Resource Inventory (NZLRI) database to provide the basis for national and regional sustainable land management planning in New Zealand. It provides a standardised assessment of land capability (what the land is capable of sustaining or producing) and determines the resource base or capacity that can be used to achieve the land’s potential.
The New Zealand Land Resource Inventory (NWASCO 1975–1979; NZLRI geographic information systems database (accessed June 2008 – February 2010) is a national spatial land resource database at a uniform scale of 1:50 000 (Harmsworth 1996; Lynn et al. 2009) with over 100 000 land management map units (GIS polygons) for New Zealand delineated primarily on the basis of landform and a physical inventory. The NZLRI has become an integral part of regional and district sustainable land planning and policy in New Zealand. It comprises three core sets of information:
- A land management unit (map unit) based on landform (minimum size of 15 ha);
- An inventory of classified data (inside each LUC map unit) describing five physical factors (rock type, soil unit, slope angle, erosion type and degree, and vegetative cover);
- A Land Use Capability (LUC) assessment (classification) for each LUC map unit.
The NZLRI comprises 11 main regions, each with a separate LUC legend. 2nd editions of NZLRI worksheets were produced for Northland, East Coast, Wellington, part Marlborough and part Waikato - Bay of Plenty.
In the NZLRI, rock type, landforms, and soils characteristics do not change in a human time scale. However, secondary factors such as present erosion and land cover/vegetation change frequently so without regular updates these parts of the NZLRI have become out of date.
NZLRI Reliability and use
The New Zealand Land Resource Inventory (NZLRI) was collected and interpreted for the whole of New Zealand from approximately 1970 to 1982 with limited regional updates in the late 1980s and 1990s.
NZLRI maps are of a regional and national scale not farm or paddock scale. They are good for catchment-level decision-making and providing an overview of the range of LUC units and LRI characteristics occurring in and around particular land blocks. NZLRI information should never be used in isolation for on-farm decision making without more detailed mapping by a suitably qualified expert, following the Manaaki Whenua standards and protocols for farm scale mapping (Grealish, 2018).
Land resource data was originally published as a series of first-edition Land Resource Inventory hard copy worksheets at a scale of 1:63 360 (1 inch to 1 mile) projected onto maps using the NZ Yard Grid, together with supporting extended legends and reports. At 1:63 360 scale, an inventory map unit can be delineated to about 16 ha (40 acres) in size. All this national land resource data was entered into a Geographic Information System (GIS) from 1980. In the late 1980s and early 1990s 2nd edition mapping was undertaken in Northland, Gisborne-East Coast, Wellington and Marlborough Regions. In the 1990's, all NZLRI maps were re-projected from NZ Yard Grid into NZ Map Grid, without updating any of the underlying NZLRI data. This effectively led to the 1:63 360 maps being reproduced at 1:50 000 scale. At 1:50 000 scale, an inventory map can be delineated to 10ha.
Visit the LRIS portal to access this data.
The LUC system of land classification assesses land in terms of its capacity for long-term, sustained productive use and indicates its degree of versatility. A physical inventory must be carried out before the land is classified for LUC. It is a national standardised classification for New Zealand that classifies land into one of eight main classes, Class 1 to Class 8. The LUC classifies land management units based on a detailed inventory: rock type, soil, slope, erosion, vegetation, climate, and land use practices (e.g. information from past and present land use). It also incorporates erosion history, and present and potential erosion severity for the assessment. The LUC classification therefore takes into account physical limitations, climate, land management requirements, past land-use history (e.g. flood history and risk), and soil conservation needs. It assesses land under the assumption of best practice.
The LUC system is hierarchical and has three main levels: class, subclass and unit. The classification has three key hierarchical components:
- LUC class (the most general level)
- LUC subclass (subdivides the LUC class on dominant physical limitation), and
- LUC unit (detailed descriptions of similar map units within each LUC subclass – ordered according to severity of limitation within each region).
The LUC class is the broadest category in the Land Use Capability (LUC) system of land classification. It is an assessment of the versatility of land for sustained agricultural production, taking into account its physical limitations. The NZ LUC system has eight land-use capability classes with limitations to land use increasing from Classes 1 to 8. LUC Classes 1–4 are suitable for arable (cropping) use and are most versatile (suitable for multiple land uses); LUC classes 5–8 are unsuitable for arable use and are more suited to pastoral or forestry use. While Class 6 land is relatively stable productive hill country, some areas may be unsustainable for pastoral farming. Class 7 land has severe limitations for pastoral use and is usually very steep and/or erosion prone. The limitations reach a maximum with LUC Class 8 land, which is unsuitable for agriculture or production forestry and should be managed accordingly for catchment protection or for conservation. Typical Class 8 land includes very steep mountainous terrain, cliffs, wetlands, and gravel floodplains.
|Land Use Capability class
|Description of land versatility
|Arable. Most versatile multiple-use land, few limitations for arable use
|Arable. Good versatile land with slight limitations for arable use
|Arable. Moderate limitations for arable use restricting crops able to be grown (less versatile)
|Arable. Severe limitations for arable use or cultivation. Requires careful management; more suited to specific crops or permanent pasture and forestry
|Non-arable. Unsuitable for cropping. Negligible limitations to pasture, viticulture, tree crop, or forestry
|Non-arable. Productive pastoral hill country, slight to moderate limitations or hazards to pasture, tree crops, and/or forestry
|Non-arable. Severe to very severe limitations or hazards for grazing with intensive soil conservation measures, more suited to forestry
|Non-arable. Very severe to extreme limitations, requiring permanent vegetative cover and protection, unsuitable for agriculture.
Each LUC Class from 1-8 can be further subdivided into land types with generally similar levels of capability, but with different primary constraints to use, based on erodibility, wetness, soil constraints and climatic constraints. "Versatility" refers to how readily different land uses can be carried out on the whenua. LUC class 1 land is the most versatile meaning that it is suitable for sustaining most land uses. As LUC class goes from 1 to 8, land tends to be less versatile. So while lower class land may be highly suitable for specific land uses (e.g. viticulture), choices of land use will be much more limited (low versatility), and active management may be required in order to achieve sustainable production even for the most suitable agricultural use of that land.
Where land is susceptible to erosion (e), this is considered of higher significance to the capability of the whenua, because if the soil is permanently lost through erosion the whenua will take many years to develop new soil (Rosser and Ross, 2011). Amongst other issues, loss of soil, particularly carbon-rich topsoil, means loss of an ability to store moisture in dry periods, or capacity to retain supply nutrients for use by plants. There are different forms of erosion which can be broadly grouped into erosion from the soil surface, for example wind erosion, erosion by water (fluvial erosion such as rill erosion and gully head erosion), and erosion by mass movement (e.g. soil slips, earthflows).
Wetness (w) is the second most important constraint to capability of the whenua. There are broadly three forms of wetness that can present an issue: waterlogging due to a rising water table during wet periods, perching of water above a layer that doesn’t let water move through it (slowly permeable layer or pan), and flooding. Capability depends on how close the waterlogging gets to the surface, how frequently it occurs each year and for how long it occurs.
Soil (s) is the third most important constraint to capability. This limitation can be due to shallow soil, stones, rock outcrops, subsurface pans in the soil leading to a low soil water holding capacity, or a low fertility/trace element deficiency or a chemical toxicity e.g. Aluminium toxicity.
Climate is the lowest in the hierarchy of limitations to land capability. Climatic factors limiting choice of land use include the average number of growing degree days per year, the timing of the first and last frosts, annual average rainfall, evapotranspiration rates and rainfall distribution, exposure to damaging winds and exposure to salt-laden winds. Table 1 summarises the impact of each of these limitations on whenua with different LUC classes. Table 2 provides a more specific breakdown of the range of land uses that whenua in each LUC class and subclass is likely to be suitable for.
Stoniness, depth, workability
Elevation & rainfall North Island
Elevation & rainfall South Island
Minimal limitations for arable use
Suitable for a wide range of crops.
Deep, >90cm, easily worked & resilient.
Silt loam or sandy loam,
Minimal erosion risk
650 - 1500mm
650 - 1500mm
Slight limitations for arable use
Suitable for many crops.
Moderately deep 45-90cm, slightly difficult to work.
well to imperfectly drained.
Slight erosion risk under cultivation:
Wind, sheet, rill.
Moderate limitations for arable use. Soil conservation measures required.
Restricted range of crops, intensity of cultivation is limited.
Shallow 20-45cm &/or stony (5-35%) in upper 20cm), often difficult to work.
All loamy textures, loamy sand and clay,
well to imperfectly drained.
Slight to moderate erosion risk under cultivation:
Wind, sheet, rill.
Severe limitations for arable use. Intensive soil conservation measures required.
Occasional cropping but reduced range of crops and intensity of cultivation.
Very shallow <20cm &/or stony or very stony (35-70%) in upper 20cm, often difficult to work.
All loamy textures, loamy sand and clay,
well to poorly drained.
Severe erosion risk under cultivation:
Wind, sheet, rill, gully.
Negligible to slight under perennial vegetation cover.
Non-arable, high producing.
Variable, deep to very shallow (<20cm) &/or stony or very stony.
well to poorly drained.
Neg. to slight erosion risk:
Sheet, soil slip, rill, tunnel gully.
Moderate, soil conservation measures desirable.
Non-arable, suited to grazing, tree crops & forestry.
Variable, deep to very shallow (<20cm) &/or stony or very stony.
well to poorly drained.
Moderate erosion risk:
Sheet, soil slip, scree, tunnel gully.
Severe, requires active soil conservation measures.
Non-arable, with soil conservation measures suited to grazing and forestry in some cases.
Variable, deep to very shallow (<20cm) &/or stony or very stony.
well to poorly drained.
Severe erosion risk:
Sheet, soil slip, scree, gully head.
Very severe to extreme – conservation or protection uses.
Unsuitable for arable, pastoral or commercial forestry use.
Variable, deep to very shallow (<20cm) &/or stony or very stony.
well to poorly drained.
Very severe to extreme:
Sheet, soil slip, scree, gully head.
Built Up Area
Commercial, industrial or residential buildings, including associated infrastructure and amenities, not resolvable as other classes. Low density ‘lifestyle’ residential areas are included where hard surfaces, landscaping and gardens dominate other land covers.
Urban Parkland/Open Space
Open, mainly grassed or sparsely-treed, amenity, utility and recreation areas. The class includes parks and playing fields, public gardens, cemeteries, golf courses, berms and other vegetated areas usually within or associated with built-up areas.
Artificial surfaces associated with transport such as arterial roads, rail-yards and airport runways. Skid sites and landings associated with forest logging are sometimes also included.
Mines and Dumps
Bare surfaces arising from open-cast and other surface mining activities, quarries, gravel-pits and areas of solid waste disposal such as refuse dumps, clean-fill dumps and active reclamation sites.
Sand and Gravel
Bare surfaces dominated by unconsolidated materials generally finer than coarse gravel (60mm). Typically mapped along sandy seashores and the margins of lagoons and estuaries, lakes and rivers and some areas subject to surficial erosion, soil toxicity and extreme exposure.
Bare surfaces arising from mass-movement erosion generally in mountain- lands and steep hill-country.
Gravel and Rock
Bare surfaces dominated by unconsolidated or consolidated materials generally coarser than coarse gravel (60mm). Typically mapped along rocky seashores and rivers, sub-alpine and alpine areas, scree slopes and erosion pavements.
Permanent Snow and Ice
Areas where ice and snow persist through late summer. Typically occurring above 1800m but also at lower elevations as glaciers.
Typically, sparse communities above the actual or theoretical treeline dominated by herbaceous cushion, mat, turf, and rosette plants and lichens. Grasses are a minor or infrequent component, whereas stones, boulders and bare rock are usually conspicuous.
Lake or Pond
Essentially-permanent, open, fresh-water without emerging vegetation including artificial features such as oxidation ponds, amenity, farm and fire ponds and reservoirs as well as natural lakes, ponds and tarns.
Flowing open fresh-water generally more than 30m wide and without emerging vegetation. It includes artificial features such as canals and channels as well as natural rivers and streams.
Estuarine Open Water
Standing or flowing saline water without emerging vegetation including estuaries, lagoons, and occasionally lakes occurring in saline situations such as inter-dune hollows and coastal depressions.
Land regularly cultivated for the production of cereal, root, and seed crops, hops, vegetables, strawberries and field nurseries, often including intervening grassland, fallow land, and other covers not delineated separately.
Land managed for the production of grapes, pip, citrus and stone fruit, nuts, olives, berries, kiwifruit, and other perennial crops. Cultivation for crop renewal is infrequent and irregular but is sometimes practiced for weed control.
High Producing Exotic Grassland
Exotic sward grassland of good pastoral quality and vigour reflecting relatively high soil fertility and intensive grazing management. Clover species, ryegrass and cocksfoot dominate with lucerne and plantain locally important, but also including lower-producing grasses exhibiting vigour in areas of good soil moisture and fertility.
Low Producing Exotic Grassland
Exotic sward grassland and indigenous short tussock grassland of poor pastoral quality reflecting lower soil fertility and extensive grazing management or non-agricultural use. Browntop, sweet vernal, danthonia, fescue and Yorkshire fog dominate, with indigenous short tussocks (hard tussock, blue tussock and silver tussock) common in the eastern South Island and locally elsewhere.
Tall Tussock Grassland
Indigenous snow tussocks in mainly alpine mountain-lands and red tussock in the central North Island and locally in poorly-drained valley floors, terraces and basins of both islands.
Areas, of mainly former short tussock grassland in the drier eastern South Island high country, degraded by over-grazing, fire, rabbits and weed invasion among which Hieracium species are conspicuous. Short tussocks usually occur, as do exotic grasses, but bare ground is more prominent.
Herbaceous Freshwater Vegetation
Herbaceous wetland communities occurring in freshwater habitats where the water table is above or just below the substrate surface for most of the year. The class includes rush, sedge, restiad, and sphagnum communities and other wetland species, but not flax nor willows which are mapped as Flaxland and Deciduous Hardwoods respectively.
Herbaceous Saline Vegetation
Herbaceous wetland communities occurring in saline habitats subject to tidal inundation or saltwater intrusion. Commonly includes club rush, wire rush and glasswort, but not mangrove which is mapped separately.
Areas dominated by New Zealand flax usually swamp flax (harakeke) in damp sites but occasionally mountain flax (wharariki) on cliffs and mountain slopes.
Bracken fern, umbrella fern, or ring fern, commonly on sites with low fertility and a history of burning. Manuka, gorse, and/or other shrubs are often a component of these communities and will succeed Fernland if left undisturbed.
Gorse and/or Broom
Scrub communities dominated by gorse or Scotch broom generally occurring on sites of low fertility, often with a history of fire, and insufficient grazing pressure to control spread. Left undisturbed, this class can be transitional to Broadleaved Indigenous Hardwoods.
Manuka and/or Kanuka
Scrub dominated by mānuka and/or kānuka, typically as a successional community in a reversion toward forest. Mānuka has a wider ecological tolerance and distribution than kānuka with the latter somewhat concentrated in the north with particular prominence on the volcanic soils of the central volcanic plateau.
Broadleaved Indigenous Hardwoods
Lowland scrub communities dominated by indigenous mixed broadleaved shrubs such as wineberry, mahoe, five-finger, Pittosporum spp, fuchsia, tutu, titoki and tree ferns. This class is usually indicative of advanced succession toward indigenous forest.
Tall forest dominated by indigenous conifer, broadleaved or beech species.
Sub Alpine Shrubland
Highland scrub dominated by indigenous low-growing shrubs including species of Hebe, Dracophyllum, Olearia, and Cassinia. Predominantly occurring above the actual or theoretical treeline, this class is also recorded where temperature inversions have created cooler micro-climates at lower elevations e.g. the ‘frost flats’ of the central North Island.
Mixed Exotic Shrubland
Communities of introduced shrubs and climbers such as boxthorn, hawthorn, elderberry, blackberry, sweet brier, buddleja, and old man’s beard.
Matagouri or Grey Scrub
Scrub and shrubland comprising small-leaved, often divaricating shrubs such as matagouri, Coprosma spp, Muehlenbeckia spp., Casinnia spp., and Parsonsia spp. These, from a distance, often have a grey appearance.
Shrubs or small trees of the New Zealand mangrove (Avicennia marina subspecies australascia) growing in harbours, estuaries, tidal creeks and rivers north of Kawhia on the west coast and Ohiwa on the east coast.
Production Exotic Forest
Forest - Harvested
Predominantly bare ground arising from the harvesting of exotic forest or, less commonly, the clearing of indigenous forest. Replanting of exotic forest (or conversion to a new land use) is not evident and nor is the future use of land cleared of indigenous forest.
Planted or naturalised forest predominantly of radiata pine but including other pine species, Douglas fir, cypress, macrocarpa, larch, acacia and eucalypts. Includes evergreen or deciduous shelterbelts.
Production forestry is the main land use in this class with minor areas devoted to mass- movement erosion-control and other areas of naturalised (wildling) establishment.
Other Exotic Forestry
Exotic deciduous woodlands, predominantly of willows or poplars but also of oak, elm, ash or other species. Commonly alongside inland water (or as part of wetlands), or as erosion-control, shelter and amenity plantings.
Soils are the biologically active skin of the earth that sustains life. Forty percent of all biomass (the weight of all living creatures, including trees, cows, people) (Bar-On et al., 2018) on earth occurs below ground. Soils in Aotearoa vary between 5cm deep and greater than 100cm deep. Soils are considered very shallow, shallow, moderately deep or deep if they have depth ranges of 0-20cm, 21-45cm, 46-60cm, or 61-90cm+. Soils can be young or old and have diverse whakapapa and inherent soil properties/characteristics of mauri. As a result, this diversity of characteristics of mauri make for a diversity in capability of the land to provide services to ecosystems (e.g. the ability to act like sponges to store water for dry spells and lessen the effect of droughts, or conversely the ability to drain water away and not allow plants to get waterlogged). Different soils also have different vulnerabilities and strengths. The main factors that influence soil formation and development, and soil variation and pattern, are climate, soil parent materials (coverbeds and underlying rock type), biological properties, people, landform, and age of the soil.
Soil Parent Materials
Soil parent materials include both coverbeds and rocks. Coverbeds are young, loose sedimentary layers that often fit across the landscape like a skin. Rocks are more dense and make the shape of the land. Soils can be developed from either coverbeds or rocks.
Coverbeds include sediments carried by wind (aeolian sediments), by streams (alluvial sediment), or by gravity as in by a landslide (colluvium). Different types of aeolian sediments include wind-blown silt from massive old riverbeds (loess, Lo), volcanic ash or “tephra” (Ng, Lp, Kt, Tp, Mo), or dune-sands (Wb). Sediment from streams is all called alluvium (Af). Colluvium from landslides is given the same symbol as alluvium (Af) unless the deposit is stony or rocky (Cl).
Rocks, as opposed to coverbeds, can be soft or hard, and organic or mineral. Soils developed from organic materials include peat soils (Pt) and soils developed under ngahere. These “rocks” are constantly growing unless drained (causing consolidation) or cultivated (causing death and rotting of the peat). Mineral soils can be weathered into hard (Gw, Si, or Ar) or soft rocks (Sm, Sb, Mm, Mb, Mf, Me, Cw, Ac), or into coverbeds.
Different coverbeds and rocks change into soils at different rates. For example, a soil developing on a hard sheet of lava (Vo) might take a lot longer to become deep than a soil developing on a soft sandstone (Sm). This rate of soil formation can also be affected by other factors such as climate.
Different parent materials provide different nutrients and minerals to the soil, depending on the composition of the original rocks (coverbeds are also originally made from rocks). Rocks are either volcanic, sedimentary or metamorphic. In New Zealand there are many kinds of volcanic, sedimentary and metamorphic rocks because our landmass sits on the boundary between the Indo-Australian and Pacific tectonic plates.
Sedimentary rocks are the most common rocks in Aotearoa, with hard rocks occurring in most of the main ranges throughout the motu, with gravels from those hard rocks in many of the current or historic riverbeds flowing from those maunga. There are a lot of soft, erosion-prone sedimentary rocks located in the North Island and in the East Coast of the South Island from Marlborough to Oamaru. Sedimentary rocks are made up of sediments from rivers and oceans, landslides, wind-blown dust (loess), or volcanic ash and are often all mixed up. The individual grains within these rocks can be from several different sources and have both different minerals in them, and be of different sizes (pebbles, sand, silt, or clay). The hardness of sedimentary rocks depends on how deeply these sedimentary rocks have been buried over millions of years. Hard rocks often make tall steep mountains and hillsides, that have shallow soils. Some sedimentary rocks are influenced by shell-fish and have a high amount of calcium carbonate present (limestones and dolomite (Li)).
Large areas of volcanic rocks occur in the Central North Island, Taranaki, the Waikato and Bay of Plenty, Auckland, Northland, and at Banks Penninsula and Dunedin. These include dark rocks such as basaltic scoria (Sc) or lava (Vo) from Rangtitoto or Ruapehu, and white pumice or ignimbrite (Vo) (formed from hot tsunami-like avalanches of ash) from volcanoes like Rotorua and Taupo. Light coloured volcanic rocks from Taupo compared with dark coloured volcanic rocks from Rangitoto Island or Pirongia. In general, the darker the colour of the rock, the deeper in the earth it has come from and the more iron and magnesium is available to the soil. The darker rocks make soils that are more fertile.
Metamorphic rocks generally occur in the maunga of the lower and central South Island and include schist (Sx, Sy) and gneiss (Gs). These are rocks that have been buried, compressed and heated until they change (metamorphose). When schist weathers it produces white quartz gravels (Gr) look very different in roads, riverbeds and terraces in the South Island compared with other parts of the country that tend to have grey coloured sedimentary gravels.
Rocks dissolve and create soil at different rates. One of the most important factors influencing this is the size of the particles in the rock itself. Rocks made from sand grains take longer to weather and release their nutrients to the soil than rocks made from silt sized grains. Rocks made from clay-sized grains are much faster to weather and produce soils than either rocks made of sand or silt-sized grains.
This layer is an expression of the percentage of the area of the map units covered by rock outcrops or surface boulders. The classes originate from and are described more fully in Webb and Wilson's Manual of Land Characteristics for Evaluation of Rural Land.
Soils can develop differently in different ecological settings e.g. nutrients leach out of upper soil layers and become more acidic (lower pH) when under trees like Kauri or Rimu which can cause Podzol soils to form around their root-zones. In comparison other vegetation such as Apple trees form nutrient-rich layers in the upper layers of the soil and the soils maintain a more balanced pH.
Current and historic vegetation and ecosystems
The speed that it takes for development of a soil e.g. the time available for soil development before erosion (e.g. by a landslide), or burial (e.g. by flood sediments or volcanic ash).
Texture is a measure of the proportions of sand, silt and clay-sized particles in the soil. Soil texture is mainly provided to the soil from the soil parent material e.g. if the parent material was sandy, then the soil is likely to be sandy. If the soil has stayed for a long time in a warm, wet climate, it may change texture from being sandy or silty to being clayey, because of chemical weathering which is making the sand and clay particles disintegrate and change.
Sandy soils feel gritty and sound raspy. If your eyesight is good enough you can see the sand grains. If the sand gets into the grooves in your fingers its either made of volcanic glass or very fine sand. Sand grains take longer to weather and release their nutrients to the soil than silt or clay grains, because they have a lot less surface area compared with their volume. Sandy soils are often well drained, and rapidly permeable but don’t hold water like a sponge and get droughty. Anything poured onto these soils tends to end up in the groundwater underneath the soil.
Silty soils feel slidy or silky. Hold them up to your ear when they are moist and work it around for long enough and you will hear the popping of little air bubbles. Silty soils are often well drained and moderately permeable, but also hold water like a sponge. These soils take time for effluent or water to trickle down through the soil, allowing the soil to treat the water before it gets to the groundwater below the soil profile.
Clayey soils feel buttery and sticky. You can model with them like potters clay. Soils made from clay-sized grains are much faster to produce nutrients than either rocks made of sand or silt-sized grains. Clay soils hold a lot of water, but they don’t drain well and have moderately slow to slow permeability. It is common for water to pond on clay soils, meaning irrigation of water or effluent, or disposal or stormwater has to be well managed to avoid unwanted flooding or run-off to waterways. Clay soils hold a lot of water like a sponge, but more like a jealous sponge that doesn’t want to give the water back. This is because they have very small pores. This water is not useful for many plants to survive in dry periods, but as long as effluent is applied slowly, the slow progress of water through these pores gives much more time for the water to be well treated by the clay soil.
Most soils in Aotearoa are a mix of sand, silt and clay called a loam. Where something is called a sandy loam or a clay loam it means it is a mix of sand silt and clay but it has more sand or more clay respectively. If the soil texture is a loamy sand then the it means it’s mostly sand with some mix of clay and silt as well but in much smaller proportions.
Potential rooting depth describes the minimum and maximum depths (in metres) to a layer that may prevent root growth. This can happen not just because of the soil layer/horizon being dense, but because of reasons such as poor aeration for roots or very low available water capacity.
Current and historic land use
Humans form part of the ecosystem that surrounds soil and as such can cause soils to change, either slowly as in the case of long term repeated cultivation or addition of biochar, or quickly like when soil is added or removed using a bulldozers and trucks or when it is artificially drained or fertilised. These soils are common in urban areas but also occur around roads, railways and quarries throughout Aotearoa.
For a mature soil to form it first has to be in a stable location. Secondly, the location of the soil will impact on what water, clays and nutrients drain into or out of the different layers of the soil. In both these cases the shape and slope angle of the landscape is important. The landscape is normally dictated by rock type, jointing and dip angle of the rock, and the aspect and angle of the slope.
Landforms impact on how soil parent materials settle/become exposed to the weather and become soils. Examples of landforms are: mountains, hills, uplifted benchs, tilted blocks/dip slopes, valleys, terraces, floodplains. Landforms can be further separated into a range of smaller units, right down to separate part of landforms, one of which is called "landform elements". These landform elements could be 1-2m or 20-50m in length depending on the topography in the area. Landform elements include: plateaux, plains, ridge, planar slope, spur nose, spur foot, hollow, spur foot, foot, hollow spur, and valley floor.
All soils are like sponges. They are full of holes called pores. Pores come in big, medium and small sizes. In some soils there are a lot of pores and the pores are well connected, like good reticulation on a farm or pipework in a house. In other soils this is not the case. Provided the pores are connected together well and there are plenty of them, soils with bigger pores will behave quite differently to soils with medium or small sized pores. This is related to the texture and the structure of the soil. The impact of texture on water holding capacity is described above in the section titled Particle Size, or “Texture”. If a soil has good structure, it has lots of small aggregates called “peds”, all joined together with pores. For a soil to hold water for plant use, it’s pores must be able to transmit water. Just like people’s arteries soil pores get clogged over time, with clay, rust and organic matter. Deep, friable, well-structured silty loamy soils hold large amounts of plant available water. Shallow soils on rock, or hard pans in the soil that don’t let water or roots through hold less water because there is less pore space. The same goes with soils with gravel and rock outcrops. Where there are rocks there is no ability to hold water, except for Pumice gravels which do have pores. They act in a similar way to the rest of the soil, but even though Pumice Soils can hold a lot of plant available water, the water drains out faster than in other soils, so they are droughty.
To understand permeability, first read “Available Water Holding Capacity” to understand how texture, structure, stoniness and porosity are linked together in determining how water moves through soil.
Every layer or “horizon” in a soil (the dark brown topsoil, the weathered, coloured layer under the topsoil called the subsoil, and the parent material layer at the bottom of the soil profile) can have a different permeability class: rapidly, moderately or slowly permeable. The slowest permeability class out of all the horizons in a soil profile is selected as the overall permeability class for that soil. For example, if a deep loamy soil has moderate permeability in its topsoil, subsoil and parent material horizons, its overall permeability class is moderately permeable. However, if a shallow soil has moderate permeability in its friable, loamy topsoil but in its subsoil, there is a slowly permeable unstructured clay-pan, then the overall permeability class of that soil is slowly permeable. It is preferable to have a soil that is moderately permeable if you want to grow things in the whenua. Rapidly permeable soils are good at preventing ponding. Slowly permeable soils have to be managed with more care to prevent waterlogging or ponding and often require artificial drainage for agricultural use, though this comes at the risk of creating environmental degradation through addition of new pathways for nitrates to bypass the natural soil drainage system and rapidly enter manga or awa.
The soil drainage classification is a way to measure the extent to which a subsoil is waterlogged during an average year. There are two types of waterlogging that are considered in the soil drainage category. One is due to soils in low-lying areas where during wet periods the water table rises up from under the soil profile and sits perhaps for some weeks closer to the soil surface than it would in summer time. The other form of waterlogging considered in the soil drainage category is where a slowly permeable pan (no structure, or the pore network is blocked like hardened arteries) is stopping the water that infiltrates from the soil surface from draining away. Many soils on terraces and rolling (8-20°) downlands have these perched water tables in Northland, Waikato, Manawatu, Hawke’s Bay, Marlborough, Canterbury, Otago and Southland.
The higher water tends to sit in the soil profile the more poorly drained a soil is classed. It is also important whether this occurs for only 1 or 2 days, 3-4 days, 10 days, or 2-3 months at a time. The classes are:
- Very poorly drained
- Poorly drained
- Imperfectly drained
- Moderately well drained
- Well drained.
Only peat soils are classified as very poorly drained. For these to form, water has to sit for long periods of time at or above the soil surface. This would present a significant impediment for many land uses. Poorly drained soils have a grey layer within 15cm of the base of the topsoil, or within 30cm from the soil surface. The grey layer represents the level that water sits for at least 7-10 days at a time during wet periods. For many land uses this creates issues if the water table is high when trying to access paddocks for purposes such as feeding out or cultivation. They will also pug badly at these times causing significant damage to perennial crops and to the structure, and pores in the topsoil. In terms of nutrients it is important to manage when nitrogen and potassium is stored in these soils (from fertiliser, supplementary feed, cow urine patches, farm dairy effluent). Reserves of these nutrients should be used up prior to times of the year when the soils are likely to be waterlogged, or the nutrients will be lost to the environment, either through leaching or loss to the atmosphere at nitrogen gas (not an environmental issue, but an expensive waste). Poorly drained soils that get waterlogged when horticultural crops such as kiwifruit experience bud-break will lead to poor crop performance or crop mortality. Imperfectly drained soils are a lot more versatile than poorly drained soils. Moderately well drained soils get waterlogged so low in the soil profile (up to about 60cm from the soil surface) that for most shallow rooting and medium depth rooting crops these soils are treated in the same class as well drained soils. Imperfectly drained and moderately well drained soils have black or rusty mottles as well as grey mottles. Rusty and black mottles are zones where iron or manganese ions have dissolved when the soil is saturated and clustered together because of electrical forces to make brightly coloured spots in the soil. Grey layers or grey mottles are the areas where the iron and manganese having washed away after being dissolved. They only get grey if they are saturated a lot, for long periods of time. Having a balance of imperfectly drained soils and poorly drained soils on a property alongside moderately well drained or well drained soils can be an advantage during droughts because they stay productive for longer where there is no irrigation.
Phosphorus (P) is a key nutrient for the successful growth of crops and pastures. P retention or ASC (Anion Storage Capacity) is an estimate of the soils capacity to fix phosphate. This is a test commonly used by fertiliser companies, but it can be important to test not just the topsoil but the subsoil too. If a soil has a high P retention (86-100%) the soil holds onto the phosphorus tightly. This is good where you are applying wastewater or effluent where you need to strip out the phosphorus for the sake of manga and awa, but it means you have to apply a lot more phosphate fertiliser than in other soils to get Olsen P levels up for good production to be possible (expensive). Soils with a high P retention or high ASC are very good soils for working, for friability and plant root growth, for holding moisture and other nutrients in a way that is available for plants to use, so they are highly sought after. Such soils occur in high rainfall mountain environments in the South and North Islands, and throughout Waikato, Bay of Plenty, Taranaki, Manawatu-Whanganui and Hawke’s Bay regions where there is volcanic ash parent material present and the rainfall is generally above 1,150mm/year and consistent through summer (i.e. “summer safe country”).
If the soil has a low (0-30%) P retention, the soil lets the phosphorus escape (e.g., a large proportion often ends up in manga, awa and roto). Such soils are located throughout the soft, erosion-prone sedimentary landscapes of the Waikato, Taranaki, Manawatu-Whanganui, Hawke’s Bay, Greater Wellington and Marlborough regions. Another type of soil with the same issue also has a perched water table (slowly permeable, poorly drained), and occurs through Manawatu, Hawke’s Bay, Marlborough, Canterbury, Otago and Southland on terraces and rolling (8-20°) downlands.
Current climate and the climate during past glaciations:
- Long term average rainfall;
- Cloud cover and amount of sunshine;
- Evaporation rates;
- Frost frequency;
- Regularity of intense rainstorms; and
- Salt-levels in coastal winds.
Note climate differs from weather. Weather is what happens on a day-by-day basis. Climate refers to longer-term conditions that are typical of a site.
This is the long term annual average temperature for a certain location in Aotearoa. This temperature value differs for each land use. For example, kiwifruit need an optimal temperature of between 21-30 0 C during the growing season.
This is the long term annual average for the amount of sunshine radiating to the surface of the whenua. This value differs for each land use. Often Growing Degree Days are used in preference to solar radiation for land use suitability assessments.
This is the long term annual average for the amount of rainfall in millimetres reaching a square metre of soil every year. Every land use requires water but at different rates at different times of the growing season. Most land uses requires evenly distributed rainfall except at the time of harvest when it needs to be dry to prevent fungus or germination of seeds in the seed heads prior to harvest.
Growing Degree Days
The amount of sunshine can be measured as sunshine hours or Growing Degree Days e.g. GDD>5°C or GDD>16°. GDD>5°C is the number of days of the year that the average air temperature is greater than a base temperature of 5°C. For pasture GDD5 is commonly used, for crops and horticulture GDD above 16°C is the standard value. Many crops also use a GDD>1O°C value. For example kiwifruit need 1 100 GGD with a base of 1 O °C between October and April.
Frost Free Days
This is the number of days between the average first frost and last frost in a given part of Aotearoa. Land uses such as kiwifruit, citrus and avocados require a larger number of frost free days in a growing season than peas, swedes or pasture grass.
Bar-On, Y.M., Phillips, R., Phillips, M., Ron (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences of the United States of America. 115 (25). Pp. 6506-6511. https://doi.org/10.1073/pnas.1711842115.
Rosser, B.J., Ross, C.W. (2011). Recovery of pasture production and soil properties on soil slip scars in erodible siltstone hill country, Wairarapa, New Zealand. New Zealand Journal of Agricultural Research Vol. 54, No. 1, pp 23-44.Scroll To Top