23  The New Zealand Soil Classification

Classifying a profile according to the NZSC (Hewitt and MWLR Pedology Staff, 2024) requires the following steps:

• Identify diagnostic features
• Follow the Key to Soil Orders
• Follow the Keys to Group and Subgroup

23.1 Identifying Diagnostic features

The descriptive parameters that help define the NZSC Diagnostic features are outlined in Table 23.1; see (Hewitt and MWLR Pedology Staff, 2024) for the full definitions. Any or all of the listed parameters may be required for a confident diagnosis.

Table 23.1: Description requirements for NZSC Diagnostic Features (Hewitt and MWLR Pedology Staff, 2024)

Diagnostic feature	Identification requirements
Horizons, pans and layers
Argillic horizon	Horizon thickness Horizon boundary distinctness Texture (relative to overlying horizon) Coatings or lamellae
Brittle-B horizon	Structure Roots Consistence: Mode of failure
Calcareous horizon	Calcium carbonate concentrations and/or coatings Field test: Calcium carbonate
Cutanic horizon	Coatings
Cutanoxidic horizon	Structure Texture Consistence: Mode of failure, stickiness, plasticity
Densipan	Consistence: Unconfined strength, penetration resistance Field test: Slaking
Distinct topsoil	Horizon thickness Matrix colour (relative to deeper horizon)
Duripan	Pans Field test: Reaction to HCl, slaking
Eluvial horizon	Structure Matrix colour Texture
Fragipan	Structure Roots Consistence: Mode of failure, unconfined strength, penetration resistance Field test: Slaking
Humus-pan	Structure Matrix colour Pans Consistence: Mode of failure, unconfined strength, penetration resistance
Ironstone-pan	Horizon thickness Horizon boundary distinctness (upper) Pans Consistence: Induration
Nodular horizon	Concentrations
Ortstein-pan	Horizon thickness Horizon boundary distinctness (upper) Pans Consistence: Unconfined strength, penetration resistance
Oxidic Horizon	Structure Texture Consistence: Unconfined strength, ped strength, mode of failure stickiness, plasticity Field test: NaF, slaking
Peaty topsoil	Horizon thickness Texture
Placic horizon	Horizon thickness Horizon boundary distinctness (upper and lower) Matrix colour Consistence: Induration
Podzolic-B horizon	Horizon thickness Structure Matrix colour Coatings and concentrations Consistence: Unconfined strength Field test: NaF
Redox-mottled horizon	Matrix colour Colour patterns
Reductimorphic horizon	Matrix colour Colour patterns Texture
Slowly permeable layer	Structure Texture Consistence: Penetration resistance
Weathered-B horizon	Matrix colour (relative to deeper layers) Structure (relative to deeper layers) Evidence of carbonate loss (relative to deeper layers)
Soil materials and contacts
Allophanic soil material	Field test: NaF Consistence: Unconfined strength, sensitivity, stickiness
Anthropic soil material	Artefacts and/or plastics Recent site disturbances Landform (Human-induced) Colour patterns
Lithic contact	Substrate rock presence Horizon degree of weathering
Organic soil material	Matrix colour Texture Consistence: Mode of failure
Paralithic contact	Substrate rock presence Horizon degree of weathering Roots Colour patterns
Saline soil material	Field test: Electrical conductivity Concentrations and/or coatings
Tephric soil material	Lithology Mineralogy
Vitric soil material	Rock fragments Texture Lithology Parent material origin Mineralogy
Profile forms
Gley profile form	Horizon depths Matrix colour Colour patterns
Mottled profile form	Horizon depths Matrix colour Colour patterns
Features
Fluvial features	Horizon thickness Horizon boundary distinctness Rock fragments Texture Consistence: Fluidity
Perch-gley features	Matrix colour Colour patterns Concentrations and/or coatings
Sodic features	Structure Matrix colour Field test: Dispersion
Other differentiae
Crumb structure	Structure
Reactive-aluminium test	Field test: NaF
Redox segregations	Concentrations

23.2 Following the Key to Orders

In addition to the diagnostics above, successful navigation of the Key may require documentation of the following:

Table 23.2: Additional description requirements for NZSC Key to Orders (Hewitt and MWLR Pedology Staff, 2024)

Order	Requirement
Anthropic Soils	Evidence of profile truncation (compare site with surrounding landform(s))
Organic Soils
Gley Soils	Buried horizons Consistence: Fluidity Field test: Reducing conditions
Ultic Soils	Structure Matrix colour Texture Clay content (relative to silt) Field test: pH
Podzols	Field test: pH
Allophanic Soils
Pumice Soils
Melanic Soils	Lithology Surface cracking Structure Rock fragments Matrix colour Texture Degree of weathering Consistence: Stickiness Field test: Calcium carbonate, pH
Semiarid Soils	Field test: Calcium carbonate, pH
Oxidic Soils
Granular Soils	Structure Rock fragments Texture Degree of weathering
Pallic Soils	Matrix colour Field test: Dispersion
Brown Soils	Matrix colour Texture
Recent Soils	Structure Consistence: Fluidity
Raw Soils

Hewitt AE, MWLR Pedology Staff, 2024. New zealand soil classification (draft 4th edition). 4th ed. Wellington, New Zealand: Manaaki Whenua Landcare Research. https://doi.org/10.7931/DL1-LRSS-1-2010