Foreword

Many technical terms are used throughout this report in the keys and definitions. These technical terms, printed with an underline, are defined in this book in the section Diagnostic horizons and other differentiae.

Further details and other technical terms are defined or can be found in the resources noted below:

• Horizon notations are consistent with Clayden and Hewitt (1989), Clayden and Hewitt (2015), recently updated in O’Brien et al. (2025).
• Soil morphology terms are defined by O’Brien et al. (2025).
• Classes of 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, denoted as a 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, are described by are defined by Churchman (1986) and Whitton and Churchman (1987) with updated overviews of soil mineralogy 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 Soil Survey Staff (2022). Note that the soil mineralogy class names given here are based on the following 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 are 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 are described by Gradwell and Birrell (1979), McQueen (1993), and Gray and Allbrook (2002), with Allbrook (1983) and Allbrook (1985) specifically targeting the physical properties of allophanic soil materials.
• A summary of the New Zealand Soil Classification is available in Hewitt (1998). 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), informs about the intentions of various aspects of the classification.
• A comprehensive overview of the diversity of soils and their properties, origins and associated landscapes in Aotearoa 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 [Internet]. 1(1):65–69. https://doi.org/10.1016/0169-1317(85)90562-9

Bigham JM, Ciolkosz EJ, editors 1993. Soil color. [Internet]. 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. [Internet]. Lower Hutt, New Zealand: New Zealand Department of Scientific; 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 14th International Congress of Soil Science, Kyoto, Japan, August 1990, Volume VII [Internet]. 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. [Internet]. Lower Hutt, New Zealand: Department of Scientific and Industrial Research. https://doi.org/10.7931/DL1-LAB-CM06

Churchman GJ, Velde B 2019. Soil clays: Linking geology, biology, agriculture, and the environment. [Internet]. 1st ed. Boca Raton, USA: CRC Press. https://doi.org/10.1201/9780429154768

Churchman JG, 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 [Internet]. Vol. 1. 2nd ed. Boca Raton, USA: CRC Press; p. 20.1–20.72. https://doi.org/10.1201/b16386

Clayden B, Hewitt AE 1989. Horizon notation for New Zealand soils. [Internet]. Lower Hutt, New Zealand: New Zealand Department of Scientific; Industrial Research. https://landcareresearch.on.worldcat.org/oclc/154214630

Clayden B, Hewitt AE 2015. Horizon notation for New Zealand soils. [Internet]. 4th ed. Lincoln, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1001

Gradwell MW, Birrell KS 1979. Methods for physical analysis of soils. [Internet]. Lower Hutt, New Zealand: Department 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 [Internet]. 108(3):287–299. https://doi.org/10.1016/S0016-7061(02)00136-2

Hewitt AE 1993. Methods and rationale of the New Zealand soil classification. [Internet]. Wellington, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-2

Hewitt AE 1998. 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, Balks MR, Lowe DJ 2021. The soils of Aotearoa New Zealand. [Internet]. 1st ed. Switzerland: Springer Nature Switzerland. https://doi.org/10.1007/978-3-030-64763-6

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

McQueen DJ 1993. Glossary of soil physical terms. [Internet]. Lincoln, Canterbury, 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 2025. New Zealand Soil Description Handbook. 3rd ed. Palmerston North, New Zealand: Manaaki Whenua Landcare Research.

Palmer AS, Lowe DJ, Almond PC 2025. Pedostratigraphy. In: Elias S, editor. Encyclopedia of quaternary science [Internet]. 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. [Internet]. https://www.pantone.com/products/munsell/munsell-soil-color-book

Soil Survey Staff 1999. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. [Internet]. 2nd ed. Washington D.C., 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. [Internet]. 13th ed. USA: National Resources Conservation Service, United States Department of Agriculture. https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/taxonomy/?cid=nrcs142p2_053580

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. [Internet]. 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. [Internet]. Lower Hutt, New Zealand: New Zealand Department 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. Lower Hutt, New Zealand: Department of Scientific and Industrial Research.