16 Secondary features

Modified

February 10, 2026

Secondary soil features are bodies formed within the soil through pedogenic (natural soil-forming) processes. They contain a higher amount of a particular substance (or association of substances) and thus contrast with the surrounding material. Many of these features create barriers to water movement or alter chemistry in a way that affects soil organisms and plant root growth.

16.1 Concentrations

Concentrations are secondary features that are not associated with specific surfaces within the soil - i.e. they do not form coatings on peds or void spaces but rather permeate the soil mass (compare with Section 16.2). Some concentrations contrast sharply with the surrounding soil material due to differences in colour, hardness, or composition, while others may be more subtle.

For rapid assessment, record concentration form and abundance percentage using Table 16.1.

For detailed assessment, note form, type, abundance in percentage, and size range in millimetres. Colour is not required as it is usually determined by type and may have already been recorded as a colour pattern (Section 14.3). Abundance and size can be classified using Table E.5 and Table E.8 respectively.

Example: NO F 10% 6-8 mm for scattered small ironstone nodules.

Table 16.1: Concentration forms

Code	Name	Description
CC	Concretion	Hard concentrations with a layered internal structure, usually rounded
NO	Nodule	Hard concentrations with no internal structure, usually irregular
CT	Crystal	A mineral arranged as interlocking or twinned macroscopic crystals or as a single macroscopic crystal, e.g., gypsum.
SS	Soft mass	A non-cemented concentration that can seldom be removed from the soil as a discrete unit
LM	Lamellae	A thin band of uncemented material with sharp upper and lower boundaries

Table 16.2: Concentration types (adapted from National Committee on Soil and Terrain (2024))

Code	Name	Description
A	Sandy	Sandy texture within a loamy, silty, or clayey matrix
E	Earthy	Loamy or silty texture within a sandy or clayey matrix
L	Argillaceous	Clayey texture within a silty, earthy, or sandy matrix
F	Ferrugineous	Iron-dominated minerals
M	Manganiferous	Manganese-dominated minerals
N	Ferromanganiferous	Dominated by a mix of iron and manganese
K	Calcareous	Dominated by calcium carbonate (CaCO₃)
Y	Gypseous	Dominated by calcium sulfate (gypsum, CaSO₄)
Z	Salty	Dominated by salts more soluble than Calcium carbonate or calcium sulfate
S	Sulfurous	Dominated by sulfur-bearing minerals, e.g. jarosite in acid sulfate soils
O	Organic	Organic texture in a low-organic or mineral matrix
UK	Unknown	Composition cannot be reliably determined

Note 16.1: Lamellae and Lamina

Lamellae are thin bands of concentrated but uncemented soil materials, formed by pedological processes. Lamellae are usually of a finer texture than their surrounds and may also have relatively high levels of other weathering products like iron precipitates or organic matter. While their formation mechanisms are still not fully understood, presence of lamellae in a profile can signify absence of some processes (e.g. bioturbation) and presence of others (e.g. seasonal freeze/thaw activity). Lamellae usually occur horizontally or parallel to the land surface at a scale of several meters, but can exhibit a wavy character at the sub-meter scale.

Lamellae may technically qualify as distinct soil horizons. If a single lamella is evident between two contrasting horizons, then it must be described as a separate horizon rather than as a concentration. Where lamellae occur within a larger band of soil material that has consistent composition, they may be described as concentrations (e.g. LM L 10% 3-5 mm for a series of thin clay bands observed in a larger sandy layer). For more detailed discussion of lamellae, see Dijkerman et al. (1967), Rawling (2000), and Bockheim and Hartemink (2013).

By contrast, lamina are thin bands of unconsolidated material with contrasting texture that have been emplaced by water, wind, or pyroclastic activity and have yet to be significantly disturbed by profile development. These geogenic layers are primary rather than secondary profile features and are described using terminology from Section 13.5.2. No minimum or maximum thickness requirements are specified for lamina due to lack of data, but anecdotally they tend to be less than 5 cm thick.

16.2 Coatings

Coatings are layers of material that form on the surfaces of other soil features, e.g. grains, peds, or the walls of voids. Some coatings are formed by chemical precipitation, similar to concentrations, while others form as a result of selective removal processes, where the material left behind accumulates. Some coatings may be biological in origin (e.g. some ant species line their burrow tunnel walls with fine material).

To record coatings, note their type using the options in Table 16.3 and their abundance as percentage of soil surfaces covered. For rapid assessment, only record the most abundant or well-developed coating.

e.g. OG 80% for well-developed organic coats covering most ped surfaces.

Table 16.3: Types of surface coating

Code	Name	Description
CC	Clay coats	Appear to have more clay than the soil matrix. They are often different in colour from the adjacent matrix and are usually recognisable in sandy or loamy soils, but can be difficult to recognise in clayey soils.
ZC	Silt coats	Silt grains concentrated at surfaces; they may be residual concentrations resulting from clay removal, or may have moved in from horizons above
SC	Sand coats	Sand grains concentrated at surfaces; they may be residual concentrations resulting from silt and/or clay removal, or may have moved in from horizons above
OG	Organic coats	Surface features that have a moist colour value of 4 or less and are rich in organic matter compared to the interior of the solid.
SQ	Sesquioxide coats	Films of sesquioxides on interfaces or impregnating interfaces. They vary in colour depending on the composition and degree of oxidation and hydration. They are difficult to identify chemically, and the different kinds cannot normally be distinguished in the field. Ferri-manganiferous coats, however, are normally very dark brown or black and effervesce vigorously with hydrogen peroxide (H₂O₂)
MN	Manganese coats	Dark to black coatings of precipitated manganese oxides, reactive to H₂O₂.
CB	Carbonate coats	Precipitated calcium carbonate (CaCO₃). Usually pale-coloured, and reactive to HCl.
SI	Silica coats	Precipitated silica (SiO₂). Usually pale-coloured, and non-reactive to HCl.

16.3 Pans

Pans form when particular chemical compounds precipitate out of the soil solution and cement a layer of mineral particles (perhaps as a further accumulation and joining together of coatings and/or concentrations), or when particular particle size distributions and/or shape range become very tightly packed. Many pans are diagnostic in the New Zealand Soil Classification, because they can form a barrier to plant root growth or water movement.

For rapid assessment, record pan type using Table 16.4 e.g., X for a fragipan. Only record pans that are strongly developed enough to be classification-relevant. A classification-relevant pan is one that is developed enough to meet all of the relevant diagnostic requirements listed in the New Zealand Soil Classification.

Many (but not all) pans have dedicated conventional horizon names. The full definitions of those horizons are available in Chapter 19.

For routine assessment, add continuity (Table 16.5) and structure (Table 16.6), e.g., FDB for a vesicular iron-pan that has been broken up by deep ripping.

Pans can optionally be described in detail in terms of type, thickness, continuity, structure, strength and cementation. Pans comprise distinct horizons, so their thickness is defined using horizon boundaries. Their strength and cementation are assessed using Table 17.2 and Table 17.10. Codes for type, continuity and structure are given below. Note that continuity can only be observed in large pits or exposures.

Table 16.4: Types of pan

Code	Name	Description	Horizon
C	Cultivation pan	Pan comprising compressed soil, induced by cultivation (e.g. use of heavy farm machinery)
D	Densipan	Silty layers with a very high bulk density and extremely slow permeability	Ed
H	Humus-pan	Cemented by aluminium and organic matter. Common in some Podzol Soils; sometimes known as ‘coffee rock’	Bhm
F	Iron pan	Interlocking nodules of Fe(/Mn) precipitates (‘bog iron’), often at a texture contrast boundary
K	Calcareous pan	Created by the precipitation of calcium carbonate (CaCO₃)	*km (B or BC horizons)
O	Ortstein pan	Pan cemented by iron and organic matter. Common in some Podzol Soils	Bsm
P	Placic	A very thin (< 10 mm), dark, iron-dominated pan with sharp boundaries	Bfm
Q	Silica pan	Created by the precipitation of silica (SiO₂), also known as a duripan	*qm (not A horizons)
X	Fragipan	An uncemented but high-density, erosion-resistant layer common in many Pallic Soils	*x (B or BC horizons)
UK	Unknown	Pan origin cannot be clearly determined
Full identification criteria for pans with horizon notations are available in Chapter 19.

Table 16.5: Pan continuity (National Committee on Soil and Terrain 2024)

Code	Name	Description
C	Continuous	Extends as a layer with little or no break across 1 m or more.
D	Discontinuous	Broken by cracks but original orientation of fragments is preserved.
B	Broken	Broken by cracks and fragments are disoriented

Table 16.6: Pan structure (adapted from National Committee on Soil and Terrain (2024))

Code	Name	Description
L	Solid	Either no recognisable structure, or close-packed peds > 100 mm
S	Vesicular	Sponge-like structure having large pores, which may or may not be filled with softer material
C	Concretionary	Spheroidal concretions cemented together
N	Nodular	Irregular nodules cemented together
P	Platy	Plate-like units cemented together

16.4 Stress features

Stress features develop along fissures or on ped faces in soils that shrink and swell as water content changes. Stress features are usually shiny but do not differ in colour from the soil matrix. Magnification may be required to observe them clearly. Stress features will not develop in sandy soil textures (see Table 15.2).

Stress features can be optionally noted during a detailed soil description. Describe type using Table 16.7 and abundance as integer percentage of ped faces covered.

Example: SL 30% in a well-developed Vertic Melanic soil.

Table 16.7: Types of pressure face

Code	Name	Description
SL	Slickensides	Smooth faces with linear grooves, from peds sliding past each other.
PF	Pressure faces	Smooth planar faces from peds pressing against each other without sliding.

16.5 Cryofeatures

Cryoturbation refers to the physical disturbance and mixing of soil caused by repeated freezing and thawing. This process commonly occurs in soils exposed to seasonal or historic freeze and thaw cycles. Affected soils may show discontinuous horizon boundaries and physical mixing as a result of intense shrink-swell activity caused by ice formation. Freezing and thawing can also accelerate downslope movement (solifluction), often incorporating angular, poorly sorted rock fragments into the soil. These features can be recognised by examining horizon boundary characteristics (Section 12.3, Section 12.4), colour patterns from mixing (Section 14.3.1), and rock fragment characteristics (Section 13.2.1).