Understanding Soils

New Zealand soils in a nutshell

A quick summary of the nature and properties of soils appearing in the New Zealand landscape of today.

'Be it deep or shallow, red or black, sand or clay, the soil is the link between the rock core of the earth and the living things on its surface. It is the foothold for the plants we grow. Therein lies the main reason for our interest in soils.'

Roy W. Simonson, as cited in the United States Department of Agriculture’s Yearbook of Agriculture, 1957.

 

Soil diversity, and how to tackle it

One of the key characteristics of soils in the landscape is their diversity. The nature and properties of New Zealand soils change in space and over time. Sometimes it can be surprising to see the differences in soils that are only a few metres apart! In our section on 'How do soils form?' you can read about the various soil forming factors that are behind these differences. What can we do to get on top of this amazing variety of soil types?

First of all it is important to realise that – unlike plants and animals – soils form a continuum, meaning that soil changes in the landscape are gradual. And whereas you can easily identify a southern brown kiwi or a red beech tree, soils are not nearly as clearly distinguishable. Instead we use observable and measurable soil properties to distinguish the various soils and group them into different classes.

The New Zealand Soil Classification (NZSC) is our current system to name and classify soils across the country. It helps us to conceptualise what we find, and to communicate about a particular soil and its properties. At its highest levels the NZSC has 15 so-called ‘soil orders’. These are groups of soils, each with a similar appearance, formation, or behaviour.

This map shows the distribution of soil orders in New Zealand:

Soil Map of New Zealand 1997

Soil Map of New Zealand, showing the distribution of the 15 soil orders for the North and South Island. Click to enlarge. Source: MWLR

Soils develop over time. Most soils – especially those in the South Island – are rather ‘young’ in geological terms and have formed since the end of the last Ice Age, approximately 14,000 years ago. Where soil formation can continue for a longer time (as in in warmer climates on stable land surfaces), deeper and more strongly weathered soil orders – such as Ultic or Granular Soils – will form.

This table illustrates an arrangement of NZSC soil orders according to soil age and other soil-forming factors:

Soil orders grouped by age

Soil orders grouped by age. Source: MWLR

In more scientific terms, the 15 soils orders can be characterised as follows:

Soil orders table

Orders of the New Zealand Soil Classification (NZSC) and their main characteristics. Source: Hewitt (1992).

A more elaborate key than the above is used to actually classify specific soils to soil orders. An alternative is to arrange NZSC soil orders along a timeline. Below you can see how, over time, soils belonging to a particular order develop into another, more advanced order.

Major pathways in the evolution of New Zealand soils

Major pathways in the evolution of New Zealand soils. Source: Hewitt (1998)

 

Want more information?

Explore the distribution of soils in New Zealand in our Soils Map Viewer.

Because the NZSC integrates a lot of knowledge about soils it is mainly being used by soils specialists, but you are welcome to dive deeper into this matter on our dedicated NZSC webpages.