Pallic Soils
Concept of the Order
Pallic Soils are soils with 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. Pallic Soils have water deficits in summer, and soil water surpluses in winter or spring.
Correlation
The order comprises most yellow-grey earths, associated steepland soils, intergrades between yellow-grey earths and yellow-brown earths, and intergrades between yellow-grey earths and brown-grey earths of the NZ Genetic Soil Classification. Most Pallic Soils are correlated with Alfisols and Inceptisols in Soil Taxonomy, particularly those under ustic or udic moisture regimes, with aquic conditions, or ochric epipedons.
Occurrence
Pallic Soils occur predominantly in the seasonally dry eastern part of North and South Islands and in the Manawatu.
Accessory Properties of the Order
- Low concentrations of secondary oxides. P retention is less than 30% in topsoils and, usually, in subsoils. Extractable iron and aluminium values are low or moderate with a significant proportion of secondary iron oxides occurring in redox segregations.
- High base status. Base saturation values in subsoils are high (more than 50%) except in perch-gleyed soils, where values may be lower in horizons overlying fragipans.
- Siliceous parent materials. Parent materials are predominantly loess or sediments derived from quartzo-feldspathic rocks (schist or greywacke).
- Mica/illite clay minerals. Pallic Soils usually belong either to the Illitic or to a Clay-mineralic mineralogy class.
- Slow permeability. Subsurface horizons have restricted permeability, particularly in soils with fragipans or duripans in which the permeability is very slow.
- Perched water-tables. Soils that are poorly or moderately well drained have water-tables perched on slowly permeable layers.
- Limited root depth. Potential rooting depth in most soils is limited by a subsurface horizon of high bulk density at shallow depths or by brittle silty cappings on rock fragments.
- Strongly worm-mixed. Topsoils generally have a significant proportion of worm casts and a distinct worm-mixed horizon occurs in the transition from A to B horizons. Topsoil worm activity is greatly reduced during summer periods of soil moisture deficit.
- High slaking and dispersion potential. Soil material, particularly in B horizons, is strongly dispersive and will readily slake. Topsoil structures may break down under prolonged impact by heavy machinery or by continuous tillage.
- Droughty summers, moist winters. Precipitation ranges from about 500 to 1000 mm per year. A spring surplus of soil water is common but the annual surplus is less than about 200 mm. The average annual deficit is approximately 90–200 mm/year.
- Phosphorus status. A high proportion of the inorganic phosphorus is non-occluded and a relatively high proportion of total phosphorus is in an organic form.
- Sulphur status. Levels of extractable sulphate are low.
Summary of Pallic Soils Hierarchy
| Code | Group | Subgroup | Example Series |
|---|---|---|---|
| PP | Perch-gley | Duric | pt. Poporangi |
| Argillic-fragic | Tokomaru | ||
| Fragic | Otokia | ||
| Weathered-argillic | Nalder | ||
| Argillic | Marton | ||
| Cemented | Caroline | ||
| Typic | pt. Salix | ||
| PU | Duric | Mottled | pt. Matapiro |
| Argillic-sodic | - | ||
| Argillic | pt. Matapiro | ||
| Typic | - | ||
| PX | Fragic | Argillic-sodic | Wither |
| Argillic-mottled | - | ||
| Argillic-calcareous | Grampians | ||
| Argillic | Seaview | ||
| Mottled-calcareous | pt. Cluden | ||
| Mottled | Timaru | ||
| Calcareous-sodic | pt. Grampians | ||
| Calcareous | pt. Takahe | ||
| Typic | Tima | ||
| PL | Laminar | Mottled | Pukeuri |
| Calcareous | - | ||
| Typic | Otama | ||
| PJ | Argillic | Mottled-weathered | Okuku |
| Mottled | Halcombe | ||
| Aged | Naseby | ||
| Mottled-ultic | - | ||
| Ultic | Rosedale | ||
| Sodic | - | ||
| Weathered | - | ||
| Calcareous | - | ||
| Typic | Abbotsford | ||
| PI | Immature | Mottled-pedal | - |
| Mottled | Wakanui | ||
| Calcareous | - | ||
| Pedal | Kiwi | ||
| Typic | Templeton |
Key to Groups of Pallic Soils
PP
Pallic Soils that have both a gley profile form and perch-gley features.
PU
Other soils that have a duripan.
PX
Other soils that have a fragipan.
PL
Other soils that have a brittle-B horizon and an argillic horizon that is predominantly in the form of lamellae.
PJ
Other soils that have an argillic horizon, or a cutanic horizon with sodic features within it or immediately beneath it.
PI
Other soils.
Key to Subgroups of Pallic Soils
PP - PERCH-GLEY PALLIC SOILS
Perch-gley Pallic soils occur in sites that are periodically saturated (if undrained) in winter and spring, but dry out in summer. The wetness and associated reducing conditions are indicated by grey colours on ped surfaces in horizons subjacent to the topsoil. Wetness is caused by perching of water on a slowly permeable subsurface layer, either a fragipan, argillic horizon, duripan, some combination of these horizons or other slowly permeable layer. The reductimorphic horizons are commonly acidic (pH less than 5.5).
PPU
Perch-gley Pallic Soils that have a duripan.
Duric Perch-gley Pallic Soils
PPJX
Other soils that have both an argillic horizon and a fragipan.
Argillic-fragic Perch-gley Pallic Soils
PPX
Other soils that have a fragipan.
Fragic Perch-gley Pallic Soils
PPWJ
Other soils in which the majority of rock fragments are weathered to the extent that they may easily be broken by hammer or spade, and have an argillic horizon.
Weathered-argillic Perch-gley Pallic Soils
PPJ
Other soils that have an argillic horizon.
Argillic Perch-gley Pallic Soils
PPC
Other soils that have a horizon that is cemented to the degree that it is at least weakly indurated, within 90 cm of the mineral soil surface.
Cemented Perch-gley Pallic Soils
PPT
Other soils.
Typic Perch-gley Pallic Soils
PU - DURIC PALLIC SOILS
Duric Pallic Soils occur in areas with pronounced soil moisture deficits and often have some proportion of tephra in the soil parent material or high exchangeable sodium. The total silica contents are not high but sufficient silica has been mobilised to form a pan that impedes roots and water.
PUM
Duric Pallic Soils that have a mottled profile form.
Mottled Duric Pallic Soils
PUJN
Other soils that have an argillic horizon, or a cutanic horizon that within or immediately beneath has sodic features.
Argillic-sodic Duric Pallic Soils
PUJ
Other soils that have an argillic horizon.
Argillic Duric Pallic Soils
PUT
Other soils.
Typic Duric Pallic Soils
PX - FRAGIC PALLIC SOILS
Fragic Pallic Soils occur in soil materials that are predominantly silty. A fragipan which severely restricts the movement of water and penetration of roots occurs below the base of the B horizon.
PXJN
Fragic Pallic Soils that have both
- an argillic or cutanic horizon overlying the fragipan, and
- sodic features within or immediately above the fragipan.
Argillic-sodic Fragic Pallic Soils
PXMJ
Other soils that have both
- an argillic horizon overlying the fragipan, and
- a mottled profile form.
Argillic-mottled Fragic Pallic Soils
PXJC
Other soils that have both
- an argillic horizon, and
- a calcareous horizon.
Argillic-calcareous Fragic Pallic Soils
PXJ
Other soils with an argillic horizon overlying the fragipan.
Argillic Fragic Pallic Soils
PXMC
Other soils that have both
- a mottled profile form, and
- a calcareous horizon immediately beneath the fragipan or calcareous material within prism interiors of the fragipan.
Mottled-calcareous Fragic Pallic Soils
PXM
Other soils that have a mottled profile form.
Mottled Fragic Pallic Soils
PXCN
Other soils that have both
- a calcareous horizon immediately beneath the fragipan or calcareous material within prism interiors of the fragipan, and
- sodic features within or immediately beneath the fragipan.
Calcareous-sodic Fragic Pallic Soils
PXC
Other soils that have a calcareous horizon immediately beneath the fragipan or calcareous material within prism interiors of the fragipan.
Calcareous Fragic Pallic Soils
PXT
Other soils.
Typic Fragic Pallic Soils
PL - LAMINAR PALLIC SOILS
Laminar Pallic Soils occur predominantly in fine sandy or silty loess or alluvium. Although rooting is impeded in the subsurface horizons it is not restricted to the degree that it is in a fragipan. The soils are generally slowly permeable.
PLM
Laminar Pallic Soils that have a mottled profile form.
Mottled Laminar Pallic Soils
PLC
Other soils that have a calcareous horizon.
Calcareous Laminar Pallic Soils
PLT
Other soils.
Typic Laminar Pallic Soils
PJ - ARGILLIC PALLIC SOILS
Argillic Pallic Soils have no fragipan or duric horizon but have a clay-enriched B horizon in which clay coatings occur predominantly on polyhedral, blocky or prismatic ped surfaces, on rock fragment surfaces, or within tubular pores.
PJMW
Argillic Pallic Soils that have both
- a mottled profile form, and
- rock fragments in which the majority is weathered to the extent that they may easily be broken by hammer or spade.
Mottled-weathered Argillic Pallic Soils
PJMU
other soils that have both
- an Eluvial horizon and pH less than 5.5 in some part of the argillic horizon, and
- a mottled profile form.
Mottled-ultic Argillic Pallic Soils
PJM
Other soils that have a mottled profile form.
Mottled Argillic Pallic Soils
PJA
Other soils that have hue 7.5YR or redder or hue 10YR and chroma 6 or more in some part of the argillic horizon.
Aged Argillic Pallic Soils
PJU
Other soils that have an Eluvial horizon and pH less than 5.5 in some part of the argillic horizon.
Ultic Argillic Pallic Soils
PJN
Other soils that have sodic features within or immediately beneath the argillic horizon.
Sodic Argillic Pallic Soils
PJW
Other soils that have rock fragments in which the majority are weathered to the extent that they may easily be broken by hammer or spade.
Weathered Argillic Pallic Soils
PJC
Other soils that have a calcareous horizon with an upper surface occurring within 90 cm of the mineral soil surface, or occurring within or immediately below the argillic horizon.
Calcareous Argillic Pallic Soils
PJT
Other soils.
Typic Argillic Pallic Soils
PI - IMMATURE PALLIC SOILS
Immature Pallic Soils are insufficiently developed to have fragipans, duripans or argillic horizons. They have either a brittle-B horizon, an eluvial horizon, a cutanic horizon, or slightly firm or stronger blocky, polyhedral or prismatic peds.
PIMD
Immature Pallic Soils that have both
- a mottled profile form, and
- are moderately or strongly pedal, with peds 100 mm or less in horizontal diameter, throughout the major part of the B horizon to 60 cm from the mineral soil surface, or to the base of the B horizon if shallower.
Mottled-pedal Immature Pallic Soils
PIM
Other soils that have a mottled profile form.
Mottled Immature Pallic Soils
PIC
Other soils that have a calcareous horizon with an upper surface within 90 cm of the mineral soil surface.
Calcareous Immature Pallic Soils
PID
Other soils that are moderately or strongly pedal, with peds 100 mm or less in horizontal diameter, throughout the major part of the B horizon to 60 cm from the mineral soil surface, or to the base of the B horizon if shallower.
Pedal Immature Pallic Soils
PIT
Other soils.
Typic Immature Pallic Soils