The diverse soil-forming conditions in New Zealand have led to a great variety of soil-forming processes, which have proved a useful aid in understanding the soil pattern and in sorting the soils into classes. Two main kinds of soil classification are used in New Zealand. The first is a genetic classification according to soil-forming processes and is used for scientific and general purposes. The second is a classification according to soil types and series and is used for mapping and land-use purposes.

For scientific purposes the genetic classification provides the various soil classes with precise technical names, such as “fulvic soils”. Over the years, however, the main soil groups have become better known to the layman by common names, such as “central yellow-brown earths”. It has been found practical, therefore, to retain the common names for popular use. They are set out with their technical and overseas equivalents in table 1.

For mapping purposes the basic unit of classification is the soil type which is relatively uniform in properties from the standpoint of land use. It is given a geographic name and a textural name, such as “Judgeford silt loam”, and these are supplemented where necessary by other descriptive terms, as in “Okaihau gravelly friable clay”. Where required, the soil type is subdivided into phases according to characteristics of lesser significance in soil classification but potentially significant to land use; or it may be classed with similar soils to form a series, the members of which have the same geographic name and are developed from the same kind of parent materials.

Alpine soils, bare rock, etc. (3 ¾ million acres) and coastal sands (¼ million acres).

*Including brown granualr loams from volcanic ash.

The soil complex is a compound mapping unit consisting of a mixture of two or more soil types which are too intimately associated in the soil pattern to be indicated separately on ordinary detailed soil maps. Hill soils and steepland soils are the particular soil complexes due to slope on hilly and steep terrain respectively; they are distinguished as special mapping units in New Zealand, where they are extensive and are widely used for farming and forestry. The soil association, like the complex, consists of a mixture of two or more soil types, but the soil pattern is sufficiently coarse to be resolved on ordinary detailed maps. The soil set, which is a convenient mapping unit used on general surveys in New Zealand, contains similar soils or similar assemblages of soils.

Soil maps showing these units are published in three main series: 4 miles to an inch (1: 253440) for general surveys, 1 and 2 miles to an inch (1:63360 and 1:126720) for district surveys, and 20 and 40 chains to an inch (1:15840 and 1:31680) for detailed surveys. General surveys show the main sets of soils and their general relation to land forms and are used to assist investigations and planning on the regional or national scale. District surveys show soil types or (in places) combinations of types, assist the study of local soil problems, provide a basis for assembling and distributing information related to soils, and are used directly for advising on pastoral land use. Detailed surveys delineate soil types and land-use phases, show the soil pattern in relation to farm boundaries and subdivisional fences, and are used directly for advising on intensive forms of land use, such as fruitgrowing and cash cropping.