Agriculture Reference
In-Depth Information
6.
The nomenclature of higher categories should be based, where possible, on connotative English
words chosen for their acceptability to nonspecialists.
7.
Where possible, continuity with successful parts of the New Zealand genetic classiÝcation should
be maintained.
8.
The soil classiÝcation must be valid for the main islands of New Zealand. Classes must be correlated
with Soil Taxonomy (Soil Survey Staff, 1999) to support international extension.
The application of some of these principles is illustrated following an outline of the structure
of the classiÝcation.
CLASSIFICATION STRUCTURE AND IDENTIFICATION OF THE SOIL INDIVIDUAL
The New Zealand Soil ClassiÝcation is hierarchical, comprising four categories above the level
of soil series. Classes of the order, group, and subgroup categories are deÝned in Hewitt (1993a).
Classes of the fourth category, soilform, are deÝned in Clayden and Webb (1994).
There are 15 orders (Table 14.1), 76 groups, and currently 253 subgroups. Unlike the Australian
Soil ClassiÝcation, which was developed at a similar time, the New Zealand Soil ClassiÝcation has
a prescribed number of subgroups. This does not allow the Þexibility of the Australian system, but
aids reproducibility in assignment and greater clarity in making soil survey correlation decisions.
New subgroups can be added, and a number of them were, at the time that the second edition was
printed (Hewitt, 1998). The number of soilforms is not prescribed. Soilform classes are formed
from a combination of parent material, particle size, and permeability proÝle classes (Clayden and
Webb, 1994). They are applied to subgroups in the same manner as Families are applied in Soil
Taxonomy.
The keys to orders, groups, and subgroups use diagnostic horizons, pans, layers, soil materials,
contacts, proÝle forms, features, and other differentiae. These are deÝned primarily for efÝcient
application of the keys.
The order of classes in the keys is determined mainly by considering potency and uniqueness
of class attributes. Potent attributes such as wetness, that override other attributes in their effect on
the utility of the soils, key out Ýrst. Classes with some unique character that depart clearly from
the central concept of the group are keyed out next. The assignment of key soil series also affected
Table 14.1
List of Orders of the New Zealand Soil Classification (NZSC) and Their Correlation with
Soil Taxonomy
NZSC order
Correlation with Soil Taxonomy
Allophanic Soils
Andisols excluding vitric soils
Anthropic Soils
Drastically disturbed, mixed, or truncated soils, or soils made from human-
deposited material. Mostly correlated with the Arents
Brown Soils
Dystrudepts and Dystrustepts
Gley Soils
Aquents, Aquepts, and Aquox
Granular Soils
Aquults, Humults and Udalfs, in basic igneous parent materials
Melanic Soils
Ustolls, Aquolls, Rendolls, Vertisols
Organic Soils
Histosols
Oxidic Soils
Oxisols
Pallic Soils
Aquepts, Aqualfs, Fragiaquepts, Dystrustepts
Podzols
Aquods, Orthods
Pumice Soils
Vitraquands, Vitrands, Vitricryands
Raw Soils
Entisols or not-soil
Recent Soils
Aquents, Orthents, Psamments, Fluvents
Semiarid Soils
Aridisols (mainly Xeric subgroups)
Ultic Soils
Aquults, Humults, Udults
A more detailed correlation at soil group level is given in Hewitt, 1997.
