Allophanic Soils are dominated by allophane, (and also imogolite or ferrihydrite) minerals. These stiff-jelly-like minerals coat the sand and silt grains and maintain a very porous, low density structure with weak strength. The soils are identified by a distinctly greasy feel when moistened and rubbed firmly between the fingers. The soil is easy to dig and samples crumble very easily when crushed in the hand. When moist the topsoil is usually very dark brown or black and the subsoil is usually yellow-brown.
Allophanic soils occur dominantly in North Island volcanic ash, and in the weathering products of other volcanic rocks. They also occur in the weathering products of greywacke in the South Island high country (Total area = 1,367,388 ha, 5 % of land in New Zealand).
ALLOPHANIC SOIL GROUPS: (number of subgroups)
* Perch-gley Allophanic Soils - slowly permeable with near surface waterlogging (2)
* Gley Allophanic Soils - ground water table (2)
* Impeded Allophanic Soils - hard or slowly permeable layer (3)
* Orthic Allophanic Soils - deep soils (5)
Anthropic Soils are soils constructed by, or drastically disturbed by people.
They include soil materials exposed by stripping of the natural soil, deposition of refuse or spoil, or by severe soil mixing. The original character of the soil is lost and the soil properties used to identify other soils are lost.
Anthropic Soils are most extensive in urban areas and areas that have been mined (Total area = 6236 ha, < 1 % of land in New Zealand).
ANTHROPIC SOILS GROUPS: (numbers of subgroups)
* Truncated Anthropic Soils - removal of the natural soil (2)
* Refuse Anthropic Soils - burial of the natural soil by manufactured materials (2)
* Mixed Anthropic Soils - natural soil drastically mixed (-)
* Fill Anthropic Soils - burial of the natural soil by natural materials (5)
Brown Soils have a brown or yellow-brown subsoil below a dark grey-brown topsoil. The brown colour is due to thin coatings of iron oxides which have weathered from the parent material.
The majority of Brown Soils occur in places in which summer dryness is uncommon and which are not waterlogged in winter. The precipitation is usually more that 1000 mm per year although it may be less in some stony soils.
They occur in loess, alluvium or slope debris parent materials which are little altered by weathering. The soils are however usually strongly leached and are acid with low levels of calcium and other basic cations. They are the most extensive New Zealand soils, particularly in the South Island mountains (Total area = 10,894,877 ha, 43 % of land in New Zealand).
BROWN SOILS GROUPS: (number of subgroups)
* Allophanic Brown Soils - allophane minerals, insufficient for Allophanic Soils (7)
* Sandy Brown Soils - sand or loamy sand, main coastal sands (4)
* Oxidic Brown Soils - crystalline Fe and Al oxides, insufficient for Oxidic Soils (1)
* Mafic Brown Soils - occur in basaltic or andesitic derived materials (5)
* Acid Brown Soils - extremely acid soils (6)
* Firm Brown Soils - strong, poorly structured sub soil, in stable sites (9)
* Orthic Brown Soils - weak or structured sub soil, commonly on slopes or young land surfaces (8)
Gley Soils are soils that have been strongly affected by waterlogging and have been reduced to depth.
They have light grey subsoils usually with reddish brown or brown mottles. The grey colours extend to more that 90cm depth. Waterlogging occurs in winter and spring and some soils remain wet throughout the year.
They often occur in low parts of the landscape where there are high ground water tables, or in places where there are seepage?s.
Large areas of Gley Soils have been artificially drained to form productive agricultural land. They occur throughout New Zealand (Total area = 711,832 ha, 3 % of land in New Zealand).
GLEY SOIL GROUPS: (number of subgroups)
* Sulphuric Gley Soils - oxidised ferrous sulphate in esturine environments (4)
* Sandy Gley Soils - sand or loamy sand (3)
* Oxidic Gley Soils - morphology of Oxidic Soils (2)
* Recent Gley Soils - young land surfaces, usually fluvial or esturine (3)
* Acid Gley Soils - extremely acid (8)
* Orthic Gley Soils - ordinary Gley Soils, usually on older land surfaces (8)
Granular Soils are clayey soils formed from material derived by strong weathering of ancient volcanic rocks or ash.
Dry or moist soil samples may be easily parted into small hard fragments. When wetted and rubbed between the fingers the clay becomes sticky and may be easily moulded with little cracking.
Reserves of major nutrients are limited, root extension into the subsoil in impeded and drainage of water through the soil is slow.
Granular soils are only know to occur in the northern North Island (Total area = 292,787 ha, 1 % of land in New Zealand).
GRANULAR SOIL GROUPS: (number of subgroups)
* Perch-gley Granular Soils - slowly permeable with near surface waterlogging (3)
* Melanic Granular Soils - more fertile soils - moderate base saturation (3)
* Oxidic Granular Soils - less fertile soils - low CEC (5)
* Orthic Granular Soils - ordinary Granular Soils (5)
Melanic Soils have black or very dark grey topsoils. The subsoil either contains lime, or has well developed structure and is neutral or only slightly acid.
Most Melanic Soils are highly fertile soils which have formed in materials from rocks rich in calcium or magnesium. In a few soils, in mountainous areas magnesium levels are sufficiently high to be toxic to many plants.
Melanic Soils occur scattered throughout New Zealand associated with calcareous rocks or weakly weathered basaltic rocks (Total area = 322,209 ha, 1 % of land in New Zealand).
MELANIC SOIL GROUPS: (number of subgroups)
* Vertic Melanic Soils - high capacity to shrink/swell on drying/wetting (3)
* Perch-gley Melanic Soils - slowly permeable with near surface waterlogging (3)
* Rendzic Melanic Soils - limestone or calcareous rock at shallow depths (3)
* Mafic Melanic Soils - occur in basaltic or andesitic derived materials (3)
* Orthic Melanic Soils - occur in soil materials with lime or high Ca contents (7)
Organic Soils are formed in the partly decomposed remains of wetland plants (peat) or forest litter.
Some mineral material may be present but the soil is dominated by organic matter. The density of the soils is very low which results in low bearing strength.
Organic soils occur in areas where plant materials accumulate but decompose very slowly, either because of wetness as in the case of peat?s, or acidity as in the case of thick forest litters.
The soils occur in wetland in most parts of New Zealand or under forest produced acid litter in high rainfall areas (Total area = 225,681 ha, 1 % of land in New Zealand).
ORGANIC SOIL GROUPS: (number of subgroups)
* Litter Organic Soils - thick forest litter (3)
* Fibric Organic Soils - weakly decomposed peat (3)
* Mesic Organic Soils - moderately decomposed peat (2)
* Humic Organic Soils - strongly decomposed or amorphous peat (2)
Oxidic Soils are clayey soils which are dominated by crystalline aluminium and iron oxides.
A sample may be easily crushed in the hand to yield fine fragments. When wetted and rubbed between the fingers, the fragments slowly break down into a clay which is only slightly sticky and readily cracks when remoulded.
Oxidic Soils occur in clayey materials derived by strong weathering of ancient volcanic rocks or ash. Their fertility is very low as they are extremely weather and leached. They do however have stable structure and good aeration, and they may be highly productive when fertilised.
They are only known to occur in the Auckland and Northland regions (Total area = 44,090 ha, < 1 % of land in New Zealand).
OXIDIC SOIL GROUPS: (number of subgroups)
* Perch-gley Oxidic Soils - soils affected by waterlogging (2)
* Nodular Oxidic Soils - have prominent iron oxide nodules (1)
* Orthic Oxidic Soils - ordinary Oxidic Soils (3)
Pallic Soils have pale coloured subsoils, usually light yellowish brown or olive yellow, due to low contents of iron oxides.
The soils have weak structure and high density. Root extension is limited and the drainage of water through the soils is slow.
Pallic Soils occur predominantly in the eastern parts of North and South Islands and the Manawatu; in places that are dry in summer and moist in winter. In many areas the surface horizons are waterlogged in winter due to the slow drainage. The precipitation is usually between 500 and 1000 mm per year. They occur in parent materials which are not strongly altered by weathering. The soils are only weakly leached with moderate to high levels of calcium and other cations (Total area = 3.090.990 ha, 12 % of land in New Zealand).
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PALLIC SOIL GROUPS: (number of subgroups)
* Perch-gley Pallic Soils - slowly permeable with near surface waterlogging (6)
* Duric Pallic Soils - with a hard cemented pan (4)
* Fragic Pallic Soils - with a brittle, hard, uncemented fragipan (8)
* Laminar - layers of clay in the subsoil (3)
* Argillic Pallic Soils - with a clay enriched B horizon (5)
* Immature Pallic Soils - younger soils (5)
Podzols are strongly acid soils which usually have a bleached horizon immediately beneath the topsoil.
This horizon is the source of aluminium and iron oxides which have accumulated, in association with organic matter, in an underlying black, yellow brown or reddish brown horizon.
Podzols are very strongly leached and have very low contents of calcium and other basic cations. They occur in areas of high rainfall (generally more than 1500 mm per year) and are usually associated with forest species which produce an acid litter.
They are most common in Northland, North Island high country and the West Coast and high country of the South Island (Total area = 3,287,043 ha, 13 % of land in New Zealand).
PODZOL SOIL GROUPS: (number of subgroups)
* Densipan Podzols - high density pan within the E horizon (5)
* Perch-gley Podzols - slowly permeable with near surface waterlogging (10)
* Groundwater-gley Podzols - ground water table (2)
* Pan Podzols - cemented pan within the B horizon (6)
* Orthic Podzols - ordinary Podzols (2)
Pumice Soils are sandy or gravely soils that are dominated by pumice, or pumice-sand which has a high content of natural glass. Clay contents are low. Drainage of excess water is rapid but the soils are capable of storing large amounts of water for plants.
Pumice Soils occur in sandy or pumiceous volcanic ashes which are relatively young. The soils have low reserves of major place elements and are likely to be deficient in some trace elements.
They are distributed in the central North Island, particularly in the Volcanic Plateau (Total area = 1,721,087 ha, 7 % of land in New Zealand).
PUMICE SOIL GROUPS: (number of subgroups)
* Perch-gley Pumice Soils - slowly permeable with near surface waterlogging (2)
* Impeded Pumice Soils - horizon that restricts roots and water movement (4)
* Orthic Pumice Soils - Ordinary Pumice Soils (6)
Raw Soils are very young soils. They lack a distinct topsoil or fluid mud is present at shallow depths.
The soils are unaggregated and are likely to be highly erosive.
They occur in environments in which sediments are actively being deposited or eroded. These include beach sands, alpine rock areas and active screes, lagoons, tidal estuaries and braided river channels. Vegetation cover is sparse and often consists of ephemeral herbaceous plants, mosses or lichens (Total area = 709,224 ha, 3 % of land in New Zealand).
RAW SOILS: (number of subgroups)
* Gley Raw Soils - periodically or permanently waterlogged (7)
* Hydrothermal Raw Soils - in active hydrothermal areas (1)
* Rocky Raw Soils - rock near the surface (-)
* Sandy Raw Soils - sandy textures (-)
* Fluvial Raw Soils - features of water deposition (-)
* Tephric Raw Soils - from volcanic material (-)
* Orthic Raw Soils - active erosion or sedimentation but not waterlogged (-)
Recent Soils are weakly developed, showing few marks of soil-forming processes.
A distinct topsoil is present but a B horizon is either absent or only weakly expressed. The soils are generally deep rooting and fertile, unless rock or massive clay is present.
Recent soils occur throughout New Zealand in young landscapes, including alluvial floodplains, unstable steep slopes and slopes mantled by young volcanic ash. Their age varies depending up the environment and soil materials but most are less than 1000 to 2000 years old (Total area = 1,401,703 ha, 6 % of land in New Zealand).
RECENT SOIL GROUPS: (number of subgroups)
* Hydrothermal Recent Soils - occurring in inactive hydrothermal deposits (1)
* Rocky Recent Soils - very shallow rock (3)
* Sandy Recent Soils - sand or loamy sand soils (3)
* Fluvial Recent Soils - sediments deposited by water (9)
* Tephric Recent Soils - volcanic ash or other ejecta (4)
* Orthic Recent soils - ordinary Recent Soils mainly in sites that have been eroded (6)
Semiarid Soils are dry for most of the growing season. Rain water is not sufficient to leach through the soil and consequently lime and salts, accumulate in the lower subsoil.
Nutrient levels are relatively high, but the soils must be irrigated to produce a crop. The soils are very weakly weathered and because contents are organic matter and iron oxides are low, they are susceptible to erosion and reduction in topsoil porosity.
Semiarid Soils occur in the inland basins or Otago and southern Canterbury, where the rainfall is less that about 500 mm per year (Total area = 222,278 ha, 1 % of land in New Zealand).
SEMIARID SOIL GROUPS: (number of subgroups)
* Aged-Argillic Semiarid Soils - old reddish clay enriched B horizon (4)
* Solenetzic Semiarid Soils - strongly affected by sodium ions (2)
* Argillic Semiarid Soils - clay enriched B horizons (5)
* Immature Semiarid Soils - younger Semiarid Soils (4)
Ultic Soils are strongly weathered soils that have a well structured clay-enriched horizon in the subsoil.
An E horizon frequently occurs which is relatively depleted in clay. Topsoils are clayey or silty and are susceptible to structural degradation or erosion. Root extension into the subsoil is limited and the drainage of water through the soil is low.
Ultic Soils occur in clay or sandy clay material derived by strong alteration of quartz rich rocks over long periods of time.
They are most common in the northern North Island and the Wellington, Marlborough and Nelson regions. The soils are acid and strongly leached, with generally low levels of calcium and other cations (Total area = 761,716 ha, 3 % of land in New Zealand).
ULTIC SOILS GROUPS: (numbers of subgroups)
* Densipan Ultic Soils - high density pan within the E horizon (2)
* Albic Ultic Soils - prominent strongly leached E horizon (3)
* Perch-gley Ultic Soils - seasonal wetness (2)
* Sandy Ultic Soils - occur in strongly weathered aeolian sands (3)
* Yellow Ultic Soils - predominantly yellowish colour (5)