Criteria for defining the soilform: the fourth category of the New Zealand Soil Classification

Content Partner: Manaaki Whenua – Landcare Research. The New Zealand Soil Classification has 15 soil orders, each of which is divided successively into soil groups and subgroups (Hewitt 1992). This report formally introduces a new soil class, the soilform, which is a division of a subgroup based mainly on lithological characteristics. It should be emphasised that the soilform is an integral part of the NZ Soil Classification. Each soilform is defined by the (inherited) criteria that define its subgroup, as well as the additional criteria described in this report that are used for differentiating soilforms within subgroups. The "soilform" has been adopted as the name for the classes in the fourth category of the system because it has few or no connotations with earlier work in New Zealand. The "soil series" (Clayden 1991) and "soil family" (Clayden and Webb 1993) were used in earlier proposals for classes based on similar criteria to those set out here. The soilform, without a geographic name, has been introduced to avoid confusion with the soil series as used in New Zealand, and the soil series and family as used in the USA. It is planned to prepare a further report in which the soilform is related to the soil series and soil types used to identify map units in soil surveys.