Preface

The history of the New Zealand Soil Classification

The fourth edition of the Zealand Soil Classification is the culmination of a long period of development from its initiation in 1983. Preliminary draft versions 1.0 and 2.0 (Hewitt 1987; Hewitt 1989) were widely circulated for comment and testing, before the revised version 3.0 was formally published as the first edition in 1992 (Hewitt 1992a). Two further editions followed, in 1998 (Hewitt 1998a) and 2010 (Hewitt 2010). The latest (fourth) edition represents the best attempt, given the current state of knowledge, to classify New Zealand soils. As the knowledge and understanding of New Zealand soils grows, further revisions will be necessary.

The New Zealand Soil Classification is a national, hierarchical soil classification, which replaced the New Zealand Genetic Soil Classification (Soil Bureau Staff 1948; Taylor and Cox 1957; Taylor and Pohlen 1962; Taylor and Pohlen 1968; Taylor and Pohlen 1979)¹. This earlier work grew out of the need for reconnaissance mapping of the nation’s soil resources. It was successful as a unifying factor in New Zealand soil science, and it played an essential role in the development of pastoral agriculture. However, modern soil surveys and land evaluations require precise definition of classes and keys for their recognition, and a new synthesis was needed of the large body of information collected since the 1950s (Hewitt 1992b).

The first edition of the New Zealand Soil Classification was developed from the New Zealand Genetic Soil Classification and preserved various parts of it. Since then, it has further evolved through experience gained using the earlier editions and the accumulation of new knowledge. It has also been influenced by experience testing the first edition of the Soil Taxonomy (Leamy et al. 1983; Leamy et al. 1990; Hewitt 1992b), and the development of subsequent versions of the Soil Taxonomy, including the most recent edition and keys (Soil Survey Staff 1999; Soil Survey Staff 2022).

With the fourth edition we also introduce an extended appendix, which now includes an additional soil order (the Cryic Soils) and associated diagnostic criteria. This is to accommodate the soils of the Ross Sea Region of Antarctica, a focal point of Antarctic soil research, incorporating leading contributions from New Zealand soil scientists. It addresses the anomaly of New Zealand workers having to use international classifications when working in Antarctica. If, in the future, more empirical evidence emerges that taxa of the Cryic Soil Order might also be applicable to New Zealand soil environments (e.g., alpine environments of the Southern Alps), it can be moved to the top of the main soil order key.

Terminology and further reading

Many technical terms are used throughout this handbook in the keys and definitions. The most relevant technical terms are printed with an underline and defined in section 2, Diagnostic horizons and other differentiae. Further details and other technical terms are defined or can be found in the resources noted below.

• The horizon notations are consistent with Clayden and Hewitt (2015), recently updated in O’Brien et al. (2026).
• Soil morphology terms are defined by O’Brien et al. (2026).
• Classes of the Soil Taxonomy are defined by Soil Survey Staff (1999) and Soil Survey Staff (2022).
• Soil colours are defined by Pantone (2017); see also Bigham and Ciolkosz (1993) for application of colour in soil science.
• Control sections are designated parts of the soil profile/pedon (depth, depth range, or thickness) in which specified diagnostic features occur to enable a soil to be categorised at each level in the classification. For example, a certain feature must occur “within 30 cm of the mineral surface” or a specific soil will have “a layer or layers of allophanic soil material that total 35 cm or more thick … within 60 cm of the mineral soil surface.”
• A lithological discontinuity is a stratigraphic break in a soil profile/pedon that is the result of a geological (not pedological) process or event. The deposition of new geological material, such as a tephra layer or an alluvial or colluvial deposit, forms a new parent material/lithology at the land surface, burying the antecedent soil. The stratigraphic break is normally marked by textural, mineralogical, and other compositional differences between the earlier and later lithologies (Palmer et al. 2025).
• Soil mineralogy terms are explained, and the methods of clay mineral analysis described, by Churchman (1986) and Whitton and Churchman (1987). Updated overviews of soil mineralogy are provided by Churchman and Lowe (2012) and Churchman and Velde (2019).
• Soil mineralogy classes originally proposed by Whitton and Childs (1989) and Childs and Whitton (1990) are now also defined in the Soil Taxonomy Soil Survey Staff (2022). Note that the soil mineralogy class names given here are based on the control section 25 cm to 100 cm, or to a lithic or paralithic contact if shallower.
• Soil chemical terms are explained, and the analytical methods described, by Blakemore et al. (1987). Note that soil pH measurements are made in water, with a ratio of 1 part of soil to 2.5 parts of water, by weight.
• Soil physical terms are explained, and the analytical methods described, by Gradwell and Birrell (1979), McQueen (1993), and Gray and Allbrook (2002). Allbrook (1983) and Allbrook (1985) focuses on the physical properties of allophanic soil materials.
• A summary of the New Zealand Soil Classification is available in Hewitt (1998b). The fourth and fifth levels of the classification are documented by Webb and Lilburne (2011).
• A companion document, the Methods and Rationale of the New Zealand Soil Classification (Hewitt 1993), discusses the intentions behind key decisions made in the classification.
• A comprehensive overview of the diversity of soils and their properties, origins, and associated landscapes in New Zealand, on an order-by-order basis, is given by Hewitt et al. (2021).
• Many other soil science concepts and technical terms are explained, in a New Zealand context, by McLaren and Cameron (1990).

Allbrook RF 1983. Some physical properties of allophane soils from the North Island, New Zealand. New Zealand Journal of Science. 26(4):481–492.

Allbrook RF 1985. The effect of allophane on soil properties. Applied Clay Science. 1(1):65–69. https://doi.org/10.1016/0169-1317(85)90562-9

Bigham JM, Ciolkosz EJ, editors 1993. Soil color. SSSA Special Publication 31. Madison, Wisconsin, USA: Soil Science Society of America. https://doi.org/10.2136/sssaspecpub31

Blakemore LC, Searle PL, Daly BK 1987. Methods for chemical analysis of soils. New Zealand Soil Bureau Scientific Report 80. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/DL1-SBSR-80

Childs CW, Whitton JS 1990. A proposed revision of the key to mineralogy classes of Soil Taxonomy (1975). In: Transactions of the 14th International Congress of Soil Science. Vol. VII. Kyoto, Japan: IUSS; p. 10–16. https://old.iuss.org/meetings-events/world-soil-congress/index.html

Churchman GJ 1986. Towards understanding soil mineralogy I. An introduction to clay minerals in soils. Soil Bureau Laboratory Report CM6. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/DL1-LAB-CM06

Churchman GJ, Lowe DJ 2012. Alteration, formation, and occurrence of minerals in soils. In: Huang PM, Li Y, Sumner ME, editors. Handbook of soil sciences: Properties and processes. Vol. 1. 2nd ed. Boca Raton, USA: CRC Press; p. 20.1–20.72. https://doi.org/10.1201/b16386

Churchman GJ, Velde B 2019. Soil clays: Linking geology, biology, agriculture, and the environment. Boca Raton, USA: CRC Press. https://doi.org/10.1201/9780429154768

Clayden B, Hewitt AE 2015. Horizon notation for New Zealand soils. Lincoln, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1001

Gradwell MW, Birrell KS 1979. Methods for physical analysis of soils. NZ Soil Bureau Scientific Report 10C. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/DL1-SBSR-10C

Gray CW, Allbrook R 2002. Relationships between shrinkage indices and soil properties in some New Zealand soils. Geoderma. 108(3):287–299. https://doi.org/10.1016/S0016-7061(02)00136-2

Hewitt AE 1987. New Zealand Soil Classification (v. 1.0). Soil Resources Report SR15. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/DL1-SRR-15

Hewitt AE 1989. New Zealand Soil Classification (v. 2.0). DSIR Division of Land and Soil Sciences Technical Record DN2. Dunedin, New Zealand: Dept. of Scientific and Industrial Research.

Hewitt AE 1992a. New Zealand soil classification. DSIR Land Resources scientific report 19. 2nd ed. Lower Hutt, N.Z.: DSIR Land Resources. https://doi.org/10.7931/DL1-LRSS-1-1993

Hewitt AE 1992b. Soil classification in New Zealand – legacy and lessons. Soil Research. 30(6):843–854. https://doi.org/10.1071/SR9920843

Hewitt AE 1993. Methods and rationale of the New Zealand Soil Classification. Landcare Research Science Series 2. Wellington, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-2

Hewitt AE 1998b. The New Zealand Soil Classification. In: Molloy L, editor. The Living Mantle: Soils in the New Zealand Landscape. 2nd ed. Wellington: New Zealand Society of Soil Science; p. 229–243.

Hewitt AE 1998a. New Zealand soil classification. Landcare Research Science Series 1. 2nd ed. Lincoln, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-1-1998

Hewitt AE 2010. New Zealand soil classification. Landcare Research Science Series 1. 3rd ed. Wellington, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-1-2010

Hewitt AE, Balks MR, Lowe DJ 2021. The soils of Aotearoa New Zealand. 1st ed. Switzerland: Springer Cham. https://doi.org/10.1007/978-3-030-64763-6

Leamy ML, Clayden B, Hewitt AE 1983. Soil classification in the N. Z. Soil Bureau. New Zealand Soil News. 31(6):183–185. https://doi.org/10.7931/DL30-1983_VOL31_6_ORC

Leamy ML, Kinloch DI, Parfitt RL 1990. International committee on Andisols: Final report. Technical Monograph 20. Washington D.C., USA: United States Department of Agriculture, Soil Management Support Services.

McLaren RG, Cameron KC 1990. Soil science: An introduction to the properties and management of New Zealand soils. 2nd ed. Auckland, New Zealand: Oxford University Press. https://landcareresearch.on.worldcat.org/oclc/22444423

McQueen DJ 1993. Glossary of soil physical terms. Lower Hutt, New Zealand: Manaaki Whenua - Landcare Research. https://doi.org/10.7931/DL1H01

O’Brien LE, Deuss K, Eger A, Milne JDG, Clayden B, Singleton PL, Wilson AD, Soil Description Working Group 2026. New Zealand Soil Description Handbook. 3rd ed. Palmerston North, New Zealand: New Zealand Institute for Bioeconomy Science.

Palmer AS, Lowe DJ, Almond PC 2025. Pedostratigraphy. In: Elias S, editor. Encyclopedia of quaternary science. Vol. 5. 3rd ed. Oxford, UK: Elsevier; p. 749–769. https://doi.org/10.1016/B978-0-323-99931-1.00265-8

Pantone 2017. Munsell soil color book. Grand Rapids, Michigan, USA. https://www.pantone.com

Soil Bureau Staff 1948. Soil map of New Zealand. 1:2,027,520 scale. Wellington, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/hdbc-9662

Soil Survey Staff 1999. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. Agriculture Handbook 436. 2nd ed. Washington DC, USA: United States Department of Agriculture. https://www.nrcs.usda.gov/resources/guides-and-instructions/soil-taxonomy

Soil Survey Staff 2022. Keys to Soil Taxonomy. 13th ed. Washington DC, USA: National Resources Conservation Service, United States Department of Agriculture. https://www.nrcs.usda.gov/sites/default/files/2022-09/Keys-to-Soil-Taxonomy.pdf

Taylor NH, Cox JE 1957. The soil pattern of New Zealand. Soil Bureau Publication 113. Wellington, New Zealand: Department of Scientific and Industrial Research. https://doi.org/10.7931/pubser-113

Taylor NH, Pohlen IJ 1962. Genetic classification of New Zealand soils (second draft). New Zealand Soil News. 10(1):1–49. https://doi.org/10.7931/dl1-sbb-026-1

Taylor NH, Pohlen IJ 1968. Classification of New Zealand soils. In: Soil Bureau Staff, editor. Soils of New Zealand, Part 1. Wellington, New Zealand: Dept. of Scientific and Industrial Research; p. 15–33. https://doi.org/10.7931/dl1-sbb-026-1

Taylor NH, Pohlen IJ 1979. Soil Survey Method. A New Zealand handbook for the field study of soils. Soil Bureau Bulletin 25. 3rd ed. Wellington, New Zealand: Dept. of Scientific and Industrial Research.

Webb TH, Lilburne LR 2011. Criteria for defining the soil family and soil sibling: The fourth and fifth categories of the New Zealand Soil Classification. Landcare Research Science Series 3. 2nd ed. Christchurch, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-3-2011

Whitton JS, Childs CW 1989. The New Zealand experience in applying the Soil Taxonomy (1975) key to mineralogy classes, and, a proposed revision of the key to mineralogy classes. DSIR Division of Land and Soil Sciences Technical Record LH1. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research. https://doi.org/10.7931/DL1-LAB-CM14

Whitton JS, Churchman GJ 1987. Standard methods for mineral analysis of soil survey samples for characterisation and classification in NZ Soil Bureau. New Zealand Soil Bureau Scientific Report 79. Lower Hutt, New Zealand: Dept. of Scientific and Industrial Research.

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1. Note that Soil Bureau Bulletin 3, ‘A genetic classification of New Zealand soils’, was never published, except for the ‘Soil map of New Zealand’ in 1948. To reference the New Zealand Genetic Soil Classification, we cite a range of readily accessible drafts, editions and summaries representing its evolution.