Soil Order

New Zealand Society of Soil Science

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 soils 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.

Occurrence
Predominantly in North Island volcanic ash, and in the weathering products of other volcanic rocks. They also occur in the weathering products of greywacke and schist in the South Island high country (5% area of NZ).

PHYSICAL PROPERTIES - Porosity is high and the soils are rapidly permeable. Because the bulk density is very low and there is little resistance to root growth. In many soils the potential root depth is very deep Topsoils are stable and they resist the impact of machinery or grazing animals in wet weather Topsoil and subsoil horizons are friable. Erosion rates are generally low except on steep slopes or exposed sites. A pronounced loss of strength occurs on disturbance

CHEMICAL PROPERTIES - The ability to retain phosphorus is very high Natural fertility is limited

BIOLOGICAL PROPERTIES - High populations of soil organisms, particularly in A horizons

CLIMATE - Soils are usually moist with more than 1000 mm/year rainfall.

Soil groups of the allophanic soil order:
Perch-gley Allophanic Soils- periodic wetness caused by a perched water table
Gley Allophanic Soils - periodic wetness caused by a groundwater table
Impeded Allophanic Soils - have a hard layer that impedes roots and water
Orthic Allophanic Soils - ordinary Allophanic Soils.

New Zealand Society of Soil Science

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.

Occurrence
Brown Soils occur in places where summer doughtiness is uncommon (except in some stony and sandy sites) and that are not waterlogged in winter. They are the most extensive New Zealand soils (43% area of NZ).

PHYSICAL PROPERTIES - Relatively stable topsoils. Well, moderately well or imperfectly drained. Usually well-developed polyhedral or spheroidal topsoil structure.

CHEMICAL PROPERTIES - Low to moderate base saturation. Parent materials are mostly weakly weathered. Dominantly mica/illite and vermiculite clay minerals. Allophanic clay minerals in Allophanic Brown Soils.

BIOLOGICAL PROPERTIES - Large and active populations of soil organisms, particularly earthworms.

CLIMATE - Annual precipitation more than 1000 mm, soils rarely dry except for some stony and sandy soils.

Soil groups of the Brown Soils order:
Allophanic Brown Soils - thin horizon with soil properties dominated by Allophanic material
Sandy Brown Soils - dominated by sand or loamy sand to depth
Oxidic Brown Soils - similar to Oxidic Soils but with significant weatherable minerals
Mafic Brown Soils - in materials from dark-coloured igneous rocks or sediments
Acid Brown Soils - strongly or extremely acid
Firm Brown Soils - strong, apedal subsurface horizon
Orthic Brown Soils - ordinary Brown Soils.

New Zealand Society of Soil Science

Gley Soils are soils that have been strongly affected by waterlogging and have been chemically reduced to depth. They have light grey subsoils usually with reddish brown or brown mottles. The grey colours usually extend to more than 90 cm 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 groundwater tables, or in places where there are seepages.

Occurrence
Gley Soils occur throughout New Zealand, usually in low parts of the landscape where there are high groundwater tables, in places where there are seepages. Large areas of Gley Soils have been artificially drained to form productive agricultural land (3% area of NZ).

PHYSICAL PROPERTIES - High groundwater-tables. Shallow potential rooting depth. Relatively high bulk densities. Limited trafficability when wet. Drainage necessary for most agricultural development. Minimal erosion. Commonly formed in alluvial or colluvial parent materials.

CHEMICAL PROPERTIES - Segregated iron and manganese oxide mottles, concretions or nodules. Organic matter contents are generally high. With increasing wetness the soils grade into Organic Soils. Chemistry varies widely depending on the mineral origin of the soil and position in the landscape, but in low-lying sites the soils receive ions leached from soils in higher parts of the landscape.

BIOLOGICAL PROPERTIES - Many soil organisms are restricted because of anaerobic conditions due to wetness.

Soil groups of the Gley Soils order:
Sulphuric Gley Soils - sulphuric acid or the mineral jarosite in marine estuarine soils.
Sandy Gley Soils - dominated by sand or loamy sand to depth
Acid Gley Soils - strongly or extremely acid
Oxidic Gley Soils - similar to Oxidic Soils but with less iron oxide
Recent Gley Soils - on young land surfaces, mainly alluvial or estuarine
Orthic Gley Soils - ordinary Gley Soils

New Zealand Society of Soil Science

Granular Soils are clayey soils formed from material derived by strong weathering of ancient volcanic rocks or ash. Dry or moist soils samples may be easily parted into small hard fragments. When wetted and rubbed between the fingers the clay becomes sticky and may be easily mounded with little cracking.

Occurrence
Granular Soils are only known to occur in the northern North Island, particularly in the lowlands of the Waikato and South Auckland regions. Parent materials are principally strongly weathered tephras, mostly older than 50 000 years. (1% area of NZ).

PHYSICAL PROPERTIES- Polyhedral structure is usually well developed. Slowly permeable and limited root depth. Topsoils have limited workability when wet.

CHEMICAL PROPERTIES - Strongly weathered with low nutrient reserves. Usually dominated by kaolin-group clay mineralogy and usually accompanied by vermiculite. Low phosphorus status and sulphate in B horizons.

Soil groups of the Granular Soils order:
Perch-gley Granular Soils - periodic wetness caused by a perched water table
Melanic Granular Soils - less acid and higher natural fertility than other soil groups.
Oxidic Granular Soils - transitional to Oxidic Soils
Orthic Granular Soils - ordinary Granular Soils.

New Zealand Society of Soil Science

Melanic Soils have black or very dark grey topsoils that are well structured. The subsoil either contains lime, or has well developed structure and is neutral or only slightly acid.

Occurrence
Melanic Soils occupy small areas scattered throughout New Zealand in association with lime rich rocks or dark coloured (basic) volcanic rocks (1% area of NZ).

PHYSICAL PROPERTIES- Topsoil structures are usually stable with good recovery after impact. The soils shrink on drying and reswell on wetting.

CHEMICAL PROPERTIES - Natural fertility is high. Base saturation are high with particularly high exchangeable calcium or magnesium. The clay fraction is usually dominated by swelling (smectite) clays.

BIOLOGICAL PROPERTIES -Biologically active.
Soil groups of the Melanic Soils order:
Vertic Melanic Soils - clayey with high capacity for shrink-swell
Perch-gley Melanic Soils - periodic wetness caused by a perched water table
Rendzic Melanic Soils - limestone or lime rich rock at shallow depth.
Mafic Melanic Soils - on dark coloured igneous rocks or sediments
Orthic Melanic Soils - ordinary Melanic Soils.

New Zealand Society of Soil Science

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.

Occurrence
Organic Soils occur in wetlands in most parts of New Zealand or under forest that produces acid litter in areas with high precipitation (1% area of NZ).

PHYSICAL PROPERTIES- Very low bulk densities and low bearing strength and high shrinkage potential when dried. Very low thermal conductivity. High total available-water capacity. Peats are very poorly drained, litters are variable.

CHEMICAL PROPERTIES -High cation exchange capacities. Nutrient deficiencies are common. Usually strongly or extremely acid.

BIOLOGICAL PROPERTIES -High carbon/nitrogen ratios indicate slow decomposition rates. Many soil organisms are restricted because of anaerobic conditions.

Soil groups of the Organic Soils order:
Litter Organic Soils - thick litter that has accumulated under forest.
Fibric Organic Soils - in peat with plant fibres that are only weakly decomposed.
Mesic Organic Soils - in peat that is moderately decomposed
Humic Organic Soils - in peat that is strongly decomposed.

New Zealand Society of Soil Science

Oxidic Soils are clayey soils that have formed as a result of weathering over extensive periods of time in volcanic ash or dark coloured volcanic rock. Despite high clay contents the soils are friable with low plasticity and fine structure. They contain appreciable contents of iron and aluminium oxides

Occurrence
Oxidic Soils are only known to occur in the Auckland and Northland regions. Parent materials are derived from strongly weathered andesite, dolerite or basalt, rock or ash. ( <1% area of NZ).

PHYSICAL PROPERTIES- Limited root depth. Slow permeability and moderate or rapid infiltration rates. High clay contents ranging from 50 to 90%. Well developed and relatively stable structure.. Soil water deficits are common in summer.

CHEMICAL PROPERTIES - Strongly weathered with very low reserves of potassium, magnesium, calcium and phosphorus. Clays have very low cation exchange capacity at the natural pH of the soil. High phosphate retention.

Soil groups of the Oxidic Soils order
Perch-gley Oxidic Soils - periodic wetness caused by a perched water table
Nodular Oxidic Soils - prominent accumulations of iron oxide
Orthic Oxidic Soil - ordinary Oxidic Soils.

New Zealand Society of Soil Science

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 in subsurface horizons. Root extension is limited and the drainage of water through the soil is slow. Pallic Soils become dry in summer and wet in winter or spring.

Essential soil characteristics
Pallic Soils have moderate to high base status and low contents of secondary iron oxides. They have pale colours, high slaking potential, and high density in subsurface horizons.

Occurrence
Pallic Soils occur predominantly in the seasonally dry eastern part of North and South Islands and in the Manawatu. Parent materials are commonly in loess derived from schist or greywacke. (12% area of NZ).

PHYSICAL PROPERTIES - Slow permeability with limited root depth. High potential for slaking and dispersion. Susceptible to erosion. Medium to high bulk density in topsoils and generally high or very high in subsoils. Water tables where present are perched.

CHEMICAL PROPERTIES - Medium to high natural nutrient content. Low concentrations of secondary oxides with high base saturation. Dominantly mica/illite clay minerals but in some areas vermiculite and kaolin/halloisite are significant. Organic matter contents are generally low. Low sulphur status.

BIOLOGICAL PROPERTIES - Strongly worm-mixed particularly at the boundary of the A and B horizons.

CLIMATE - Droughty in summer, moist or wet in winter. Precipitation usually between 50 and 1000 mm/annum. Soil groups of the Pallic Soils order

Perch-gley Pallic Soils - periodic wetness caused by a perched water table
Duric Pallic Soils - silica-cemented pan in the subsoil
Fragic Pallic Soils - a strong, brittle, but uncemented pan in the subsoil
Laminar Pallic Soils - clay accumulation as thin bands in the subsoil
Argillic Pallic Soils - clay accumulation as thin coatings on peds or in pores
Immature Pallic Soils - Pallic Soil features are weakly expressed.

New Zealand Society of Soil Science

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. For many soil properties there are strong contrasts between topsoils and subsoils.

Occurrence

Podzol Soils occur in areas of high rainfall and are usually associated with forest trees 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. The soils occur mainly in materials from silica-rich rocks such as granite, greywacke, schist, rhyolite or rhyolitic ash. (13% area of NZ).

PHYSICAL PROPERTIES- Low bulk densities in surface horizons but frequently high in lower horizons. Cemented or compacted B horizons are common with associated slow permeability and limited root depth. E and B horizons are weakly pedal or lack pedality.

CHEMICAL PROPERTIES - Low natural fertility and low base saturation. Strongly or extremely acid. Secondary oxides and other clay minerals are strongly differentiated with depth. Usually high organic matter contents in the topsoil - frequently with an organic layer at the soil surface (L,F,H or O horizon). Phosphate retention is very low in A and E horizons but high or very high in B horizons.

BIOLOGICAL PROPERTIES- Low biological activity. The vegetation comprises plants that deposit a mor-forming acid litter.

CLIMATE - Wet climate. The soils are moist throughout the year.

Soil groups of the Podzol Soils order:
Densipan Podzol Soils - high density, pale coloured, but uncemented pan just beneath the topsoil
Perch-gley Podzol Soils - periodic wetness caused by a perched water table
Groundwater-gley Podzol Soils - periodic wetness caused by a groundwater table
Pan Podzol Soils - with a subsoil pan
Orthic Podzol Soils - ordinary Podzols.

New Zealand Society of Soil Science

Pumice Soils are sandy or gravelly 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. They occur in sandy or coarse pumiceous volcanic ashes ranging from 700 to 3500 years in age.

Occurrence
Pumice Soils occur predominantly in the central North Island, particularly in the Volcanic Plateau (7% area of NZ).

PHYSICAL PROPERTIES- Clay contents are low, generally less than 10%. Low soil strengths with very high macroporosity and deep rooting. Sensitive with low strength when disturbed. Generally resistant to livestock treading damage.

CHEMICAL PROPERTIES - The pumice is fresh or only moderately weathered with low reserves of major nutrient elements. Trace elements are likely to be deficient. Allophanic clay minerals. Phosphate-retention is moderate or high.

BIOLOGICAL PROPERTIES- Soil animal populations are low with most species concentrated in the topsoil. Earthworm populations are limited by droughtyness and coarse textures.

Soil groups of the Pumice Soils order Perch-gley Pumice Soils - periodic wetness caused by a perched water table
Impeded Pumice Soils - a subsoil layer that restrict water movement and roots
Orthic Pumice Soil - ordinary Pumice Soils.

New Zealand Society of Soil Science

Raw Soils are very young soils. They lack distinct topsoil development or are fluid at a shallow depth. They occur in environments where the development of topsoils is prevented by rockiness, by active erosion, or deposition.

Occurrence
Raw Soils occur scattered throughout New Zealand, particularly in association with high mountains (alpine rock areas and active screes), braided rivers, beaches and tidal estuaries(3% area of NZ).

PHYSICAL PROPERTIES- No B horizon and a topsoil is either absent or less than 5 cm thick. In soils with a fluid subsurface layer, a continuously high water-table is present. Non-fluid soils occur in environments with active erosion or deposition

CHEMICAL PROPERTIES - Fresh materials or weakly weathered. Fertility is limited by lack of organic matter and nitrogen deficiency.

BIOLOGICAL PROPERTIES-Vegetation cover is sparse and often consists of ephemeral herbaceous plants, mosses or lichens.

Soil groups of the Raw Soils order:
Gley Raw Soils - periodically wet
Hydrothermal Raw Soils - soils naturally warmed by geothermal activity
Rocky Raw Soils - rock at shallow depths
Sandy Raw Soils - dominated by sand or loamy sand to depth
Fluvial Raw Soils - in sediments deposited by flowing water
Tephric Raw Soils - in sediments originating as volcanic ejecta
Orthic Raw Soils - ordinary Raw Soils.

New Zealand Society of Soil Science

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.

Occurrence

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 upon the environment and soil materials but most are less than 1000 to 2000 years old (6% area of NZ).

PHYSICAL PROPERTIES - The soils are deep rooting and are well to imperfectly drained. Variable soil texture with stratification of contrasting materials common and high spatial variability. Generally high plant-available water capacity. Subsoils are either weakly pedal or lack pedality..

CHEMICAL PROPERTIES - The soil materials are fresh to moderately weathered and base saturations are usually high. Natural fertility is usually high and phosphate retention is low. The clay mineralogy is usually dominated by illite.

BIOLOGICAL PROPERTIES - A continuous cover of vascular plants is normally well established.

Soil groups of the Recent Soils order:
Hydrothermal Recent Soils - soils naturally warmed by geothermal activity
Rocky Recent Soils - rock at shallow depths
Sandy Recent Soils - dominated by sand or loamy sand to depth
Fluvial Recent Soils - in sediments deposited by flowing water
Tephric Recent Soils - in sediments originating as volcanic ejecta
Orthic Recent Soils - ordinary Recent Soils, most commonly on slopes.

New Zealand Society of Soil Science

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 of organic matter and iron oxides are low, they are susceptible to erosion and compaction.

Occurrence
Semiarid Soils occur in the inland basins of Otago and southern Canterbury, where precipitation is less than about 500 mm per year (1% area of NZ).

PHYSICAL PROPERTIES- High slaking and dispersion potential with moderate to high bulk densities. No poorly or very poorly drained soils. Soil structure is usually weakly developed. The soils are erosive.

CHEMICAL PROPERTIES -The soils are weakly buffered with low cation exchange capacity. The exchange complex may have relatively high sodium contents. Soluble salts are present in many soils, and calcium carbonate is present in most soils. Low iron and aluminium oxide contents and very low phosphate retention. High base saturation and nutral or weakly alkaline pH in some soils. Illitic clay mineralogy

BIOLOGICAL PROPERTIES- Low biological activity because of droghtyness and low organic matter contents.

CLIMATE -Precipitation ranges from about 350 to 500 mm per year.

Soil groups of the Semiarid Soils order: Aged-argillic Semiarid Soils - reddish coloured clay accumulations
Solonetzic Semiarid Soils - relatively high amount of sodium on clay surfaces
Argillic Semiarid Soils - clay accumulation as thin coatings on peds or in pores
Immature Semiarid Soils - features are weakly expressed.

New Zealand Society of Soil Science

Ultic Soils are strongly weathered soils that have a well structured clay-enriched horizon in the subsoil. An E horizon frequently occurs immediately beneath the topsoil which is relatively depleted in clay. The soils are acid and strongly leached, with generally low levels of calcium and other basic cations. They occur in clay or sandy clay material derived by strong alteration of quartz rich rocks over long periods of time. Occurrence

Ultic Soils are most common in the northern North Island, and the Wellington, Marlborough and Nelson regions (3% area of NZ).

PHYSICAL PROPERTIES - Clayey subsoils with slow permeability. Dispersible surface horizons with susceptibility to livestock treading damage. Prone to erosion where the surface cover has been removed. Moderate to high plant-available water capacity in topsoils but low in subsoils.

CHEMICAL PROPERTIES - Strong acidity with low concentrations of reserve magnesium and potassium horizons. Small content of weatherable minerals. Phosphate retention in topsoils is low or moderate. Kaolin and vermiculite are the dominant clay minerals.

BIOLOGICAL PROPERTIES - Large and active populations of soil organisms in topsoils.

Soil groups of the Ultic Soils order:
Densipan Ultic Soils - high density, pale coloured, but uncemented pan just beneath the topsoil
Albic Ultic Soils - pale coloured horizon just beneath the topsoil
Perch-gley Ultic Soils - periodic wetness caused by a perched water table
Sandy Ultic Soils- occur in weathered sands
Yellow Ultic Soils - yellow or yellow-brown colours in the subsoil.