Soils

A good soil map is a valuable basis for LUC mapping, especially on flat land and lower slopes where erosion often only plays a minor role.

Soil is an essential part of the physical nature of the landscape and therefore a key inventory factor, and the basis for productive capability of a landscape. It is one of the four limitations within LUC Subclass and it could be limiting sustainable production of the land.

However, the soil factor is one of the more difficult inventory factors to assess and source information. Much of New Zealand’s published soil information is patchy and varies in age, scale and quality.

Detailed surveys are generally restricted to the productive lowlands, while more general soils information is often all that is available for much of the hill and high country. The ability to leverage existing soils information to identify, describe and map soils in the field is an important skill in LRI assessment.

Prior to the late 1990s, most New Zealand soil information is classified in terms of the old NZ Genetic Classification (NZGC) (Taylor & Pohlen 1962, 1968), but subsequently the NZ Soil Classification (NZSC) (Hewitt 1992, 1998, 2010) has been introduced.

These two systems follow different philosophies, and there is no simple 1:1 correlation of NZGC soil groups to NZSC soil orders, or other taxa at lower levels. The table below gives some indication as to how NZSC maps onto NZGC groups.

Table 1: Correlation between the NZ Genetic Classification and the NZ Soils Classification (adapted from Molloy 1998)

NZ Soil Classification	NZ Genetic Classification	Defining characteristic
Allophanic Soils	Yellow-brown loams	Dominated by allophane clay
Anthropic Soils	Anthropic soils	Man-made soils
Brown Soils	Mainly yellow-brown earths (except northern YBEs) and some YB sands, BG, loams and clay	Distinctive brown colourations due to good aeration characteristics
Gley Soils	Gley soils or gley recent soils	Water-logged anaerobic soils
Granular Soils	Mostly brown-granular (EG) loams and clays	Distinctive granular peds and formed from well-weathered volcanics
Melanic Soils	Rendzinas, rendzic intergrades, and some brown-granular loams and clays	Distinctive rich dark topsoils with strong structural developments often associated with limestone
Organic Soils	Organic soils	Formed from organic matter (e.g., peat)
Oxidic Soils	Strongly weathered red loams, brown loams, some BG loams and clays	Clay soils cominated by oxides (rust)
Pallic Soils	Yellow-grey earths	Pale and often dense subsoils
Podzol Soils	Podzols	Heavily leached acid soils with a distinctive pale-to-white horizon
Pumice Soils	Yellow-brown pumice soils	Dominated by pumice
Raw Soils	Some recent soils, and some unclassed soils	Newly formed soils without distinct topsoils
Recent Soils	Recent soils	Young soils with distinct topsoils
Semi-arid Soils	Brown-grey earths	Formed in a semi-arid climate
Ultic Soils	Northern yellow-brown earths, some podzols and some YB sands	Strongly weathered soils with clay-rich subsoils

It is important to note that all of the original regional LUC legends and units were conceived and defined around the NZ Genetic Classification. And while NZSC attributes have been added to the NZLRI dataset, the relationship between soil sets, series and phases in the NZ Genetic Classification to the NZSC soil classification hierarchy is a many-to-many relationship rather than a simple attribute mapping exercise.

Where the NZ Genetic Classification is used, the 'Series' describes a local soil (e.g., Manawatu soils), the 'Soil Type' differentiates the soil by textural class (e.g. Manawatu fine sandy loam), and the 'Phase' indicates a distinctive characteristic like landscape position, wetness, depth, or stoniness (e.g., Manawatu fine sandy loam, mottled phase).

Series and soil type names tend to find common usage amongst farmers and farm advisors, possibly because they represent local and easy to recognise references. However, the approach is not uniform throughout NZ, and should therefore be used with caution. Officially the ‘regional soil series’ approach is now limited to two components – Series and Phases – whereby the phase includes the textural class.

In the NZSC system, the series / soil types / phases have been replaced by 'families' and 'siblings'. They represent the 4th and 5th level of the NZSC and are defined in Webb & Lilburne (2011).

S-map Online, the digital soil map for Aotearoa New Zealand, provides soils information for approx. 40% of New Zealand soils with more than two thirds (68.5%) of multiple use land (horticulture, cropping and intensive pasture systems) covered at this moment in time.

See section 2.2 of the LUC Handbook for details on soils and LUC.

The digital soil map of New Zealand

S-map Online

S-Map data includes fundamental soil property data - such as depth, stoniness, clay and sand content - created from field observations and expert knowledge, as well as derived soil data based on models (e.g., available water, macroporosity, P retention, pH, soil carbon).
The tool also allows you to create custom soil maps and download soil factsheets for specific locations.

Visit S-map Online

S-map Online factsheet browser (login required)

S-map Online also provides a Factsheet Browser which allows you to check what former soil series of the the NZ Genetic Classification have become in terms of NZSC families and siblings.

Reference documents for NZ soils

Soil Description Handbook (Milne et al. 1995)

New Zealand Soil Classification (3rd Edition, Hewitt 2010)

Criteria for defining soil family and soil sibling (Webb & Lilburne 2011)

Methods and Rationale of the NZSC (Hewitt 1993)

New Zealand Soil Mapping Protocols and Guidelines (2017 Envirolink Report)

NZ Soil Classification (NZSC)

The SoilsPortal provides more detail on the NZ Soil Classification (NZSC), a hierarchical structure with five levels:

Order: The 15 soil orders are the highest, most generalised level of the classification and provide the national overview of New Zealand soils.
Groups: The orders are divided into 74 soil groups based on variation in factors such as drainage status, parent material, chemical and physical properties.
Subgroups: The soil groups are divided into 299 subgroups that provide more detail about the range of soils included in each soil group.
Family: The soil subgroups are subdivided into family criteria that provide more detail about the soil parent materials, rock class, texture, and permeability.
Sibling: The soil family are subdivided into sibling criteria that provide more detail about soil depth, stone content, upper and lower textures, and drainage.

Soils develop over time

Most soils – especially those in the South Island – are rather ‘young’ in geological terms and have formed since the end of the last Ice Age, approximately 14,000 years ago. Where soil formation can continue for a longer time (as in in warmer climates on stable land surfaces), deeper and more strongly weathered soil orders will form.

Table 2: This table illustrates an arrangement of NZSC soil orders according to soil age and other soil-forming factors.

Young soils		Raw Soils
		Recent Soils
		Anthropic Soils
Mature soils Soils that have well developed topsoil and subsoil horizons	Climate Soils formed in quartz rich material that show the effects of climate	Semiarid Soils
		Pallic Soils
		Brown Soils
		Podzols
	Wetness Soils with prolonged high water tables	Gley Soils
		Organic Soils
	Rock soil parent materials fromed from rocks that sominate the soil character, e.g. limestone, basalt, pumice and volcanic ash	Melanic Soils
		Pumice Soils
		Allophanic Soils
Old soils On land surfaces with parent materials that have attributes of advance weathering		Ultic Soils
		Granular Soils
		Oxidic Soils

Soil orders are divided into Soil Groups based on variation in factors such as drainage status, parent material, chemical and physical properties. For example:

Raw Soils:

[WG] Gley Raw Soils — periodically wet
[WH] Hydrothermal Raw Soils — soils naturally warmed by geothermal activity
[WX] Rocky Raw Soils — rock at shallow depths
[WS] Sandy Raw Soils — dominated by sand or loamy sand to depth
[WF] Fluvial Raw Soils — in sediments deposited by flowing water
[WT] Tephric Raw Soils — in sediments originating as volcanic ejecta
[WO] Orthic Raw Soils — other Raw Soils

Recent Soils:

[RH] Hydrothermal Recent Soils — soils naturally warmed by geothermal activity
[RX] Rocky Recent Soils — rock at shallow depths
[RS] Sandy Recent Soils — dominated by sand or loamy sand to depth
[RF] Fluvial Recent Soils — in sediments deposited by flowing water
[RT] Tephric Recent Soils — in sediments originating as volcanic ejecta
[RO] Orthic Recent Soils — other Recent Soils, most commonly on slopes

Siblings

Siblings are described by a sequence of up to six functional horizons. Functional horizons are soil horizons (layers of soil material), occurring in soil profiles, characterised by clearly defined soil morphological parameters. They are functional horizons because they are used to predict soil characteristics such as profile available water and hydraulic conductivity.

The comprehensive source of NZ soils information

Soils Portal

The Soils Portal, Pātaka Oneone, is Manaaki Whenua’s website for comprehensive information about New Zealand’s soil resources. It has been running for more than 15 years, and currently attracts some 40,000 visitors per year.
It caters for a wide range of users, e.g. land managers, resource managers, teachers and students, in fact, anyone from a soil scientist to a soil ‘beginner’.

Visit the Soils Portal