Foreword.qmd

# Foreword {#sec-foreword .unnumbered}

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](Diagnostics.qmd#sec-diagnostics).

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

-   Horizon notations are consistent with @clayden1989, @clayden2015, recently updated in @obrien2025.
-   Soil morphology terms are defined by @obrien2025.
-   Classes of Soil Taxonomy are defined by @soilsurveystaff1999 and @soilsurveystaff2022.
-   Soil colours are defined by @pantone2017; see also @soilcol1993 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 [@palmer2025].
-   Soil mineralogy terms are explained, and the methods of clay mineral analysis, are described by are defined by @churchman1986 and @whitton1987 with updated overviews of soil mineralogy by @churchman2012 and @churchman2019.
-   Soil mineralogy classes originally proposed by @whitton1989 and @childs1990a are now also defined in @soilsurveystaff2022. 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 @blakemore1987. 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 @gradwell1979, @mcqueen1993, and @gray2002, with @allbrook1983 and @allbrook1985 specifically targeting the physical properties of allophanic soil materials.
-   A summary of the *New Zealand Soil Classification* is available in @hewitt1998. The fourth and fifth levels of the classification are documented by @webb2011.
-   A companion document, the *Methods and Rationale of the New Zealand Soil Classification* [@hewitt1993], 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 @hewitt2021.
-   Many other soil science concepts and technical terms are explained, in a New Zealand context, by @mclaren1990.