Describing soils

Overview: History of soil description in a nutshell

People through the ages have been describing and classifying soils in order to communicate and manage their diversity.

Describing New Zealand's soils

Māori: Pre-European Soil Classification

Soil classification in New Zealand was begun by Māori horticulturalists who recognised and named classes that were relevant to the establishment and management of their gardens, in particular, kumara gardens. They recognised classes such as oneharuru (a light but good sandy loam) and onetea (white soil from sandy volcanic material). The need for soil classification has been part of human activity in New Zealand since the arrival of the first Polynesian canoe.
See a full list of Māori soil names on the related Te Ara webpage.

New Zealand Genetic Soil Classification (NZG): The First National Soil Nomenclature

Soil classification on a comprehensive national scale was not developed in New Zealand until 1948. The pioneer New Zealand soil scientist, Norman Taylor, developed the New Zealand Genetic Classification, which recognised 'soil groups' and related them to the environmental factors that most influenced their character. Knowledge of these relationships helped the prediction of soil classes from observations of geology, landscape, climate and vegetation. Such predictions enabled rapid progress in the broad-scale exploratory mapping of New Zealand soils.

By the late 1970s, Taylor's New Zealand Genetic Soil Classification was becoming outdated. Soil classes were vaguely defined so that only experts could easily identify the correct class for many soils. The relationships between soils and environment that were useful at a broad scale were less useful for making soil maps at more detailed scales. Much new soil information was becoming available that could not be explained within the framework of the old system. A new synthesis was needed and the result was the New Zealand Soil Classification.

Regional Soil Names – Soil Series

Regional Soil Series names, sometimes known as common names, are used to distinguish similar soils at a finer level of classification than is possible with either the Genetic or NZSC classifications. One of the problems with soil series names is the use of different names for the identical soils in different regions or even for adjacent soil survey areas. Because of their wide everyday usage among farmers and farm advisors, Series names that were evolved before the existence of NZSC are still used even though in some instances they correspond to more than one NZSC category – care is therefore needed when applying these names.

Regional Soil Names – Soil Sets

Once upon a time there were also things called soil sets. Soil sets were based on soil-landscape units and contained high soil variability. They only survive in remote parts of the country that have only been mapped using the 4-mile maps – but we try not to talk about them any longer.

Present Day National Soil Classification (NZSC)

The New Zealand Soil Classification was developed in the 1980s. The top three levels of the classification (orders, groups, and subgroups) were described by Hewitt (1992, 2010 3rd edn), the fourth and fifth levels (family and sibling) by Webb and Lilburne (2011). The fourth level (soilforms) by Clayden and Webb (1994) were replaced by the family and sibling. The new classification grew out of the New Zealand Genetic Soil Classification and, where possible, preserved its useful features. The new classification was also influenced by local experience in testing the United States soil classification system 'Soil Taxonomy'. The resulting classification represents the best attempt to classify New Zealand soils, at our current state of knowledge. As knowledge and understanding of soils grows, further revisions will be necessary.

A correlation table of the Genetic Soil Classification with the New Zealand Soil Classification (NZSC) can be found here (Hewitt 2010).

Soil families in S-map

Soil families are objectively defined soil entities that consist of soils having the same Subgroup classification (New Zealand Soil Classification, Hewitt 2010) and the same set of soil physical characteristics, comprising a) soil parent material class in the top 100 cm, b) the dominant texture class in the top 60 cm, and c) the slowest permeability class in the top 100 cm.

Soil families are given a geographic name but are also identified with a 4- or 5-character abbreviated name. A geographic name, as used to name soil series, has been retained because the users of soils are familiar with this usage and geographic names help in recalling soil characteristics. The family name is suffixed with an italicised f (f) to distinguish the family from the soil series.

International Soil Classification

New Zealand soil classification systems are related to those used internationally, and for the purpose of global studies it is necessary to relate NZ nomenclature to commonly used international practice.

US Soil Taxonomy

In 1975, Soil Taxonomy was published by the United States Department of Agriculture's Soil Survey Staff. This system for classifying soils has undergone numerous changes since that time, and the 2nd edition was published in 1999. The 12th edition of the 'Keys to Soil Taxonomy' was published in 2014.

A correlation table of US Soil Taxonomy with the New Zealand Soil Classification as well as Genetic Soil Classification can be found here (Hewitt 2010).

World Reference Base for Soil Resources

The World Reference Base for Soil Resources (WRB) is the international standard taxonomic soil classification system endorsed by the International Union of Soil Sciences (IUSS). It was developed by an international collaboration coordinated by the International Soil Reference and Information Centre (ISRIC) and sponsored by the IUSS and the FAO via its Land & Water Development division. It replaces the previous FAO Soil Classification.