Soil orders

Brown Soils [B]

Our most extensive soils, covering 43% of New Zealand.

Brown Soils have a brown or yellow-brown subsoil below a dark grey-brown topsoil. The brown colour is caused by thin coatings of iron oxides weathered from the parent material.

Lismore Brown Soil. Credit - The Living Mantle
Lismore Brown Soil. Credit - The Living Mantle

Occurrence

Brown Soils occur in places where summer drought is uncommon and that are not waterlogged in winter. They are the most extensive soils, covering 43% of New Zealand.

View map View map of Brown soils.

Physical properties

They have relatively stable topsoils with well-developed polyhedral or spheroidal structure.

Chemical properties

Soils have low to moderate base saturation. Clay minerals are dominantly mica/illite and vermiculite, with allophane in Allophanic Brown Soils.

Biological properties

Soils contain large, active populations of soil organisms, particularly earthworms.

Soil groups

Soil orders are divided into soil groups based on variation in factors such as drainage status, parent material, chemical and physical properties

[BL] Allophanic Brown

Have an horizon with soil properties dominated by allophanic material

[BS] Sandy Brown

Dominated by sand or loamy sand to depth

[BX] Oxidic Brown

Similar to Oxidic Soils but with significant weatherable minerals

[BM] Mafic Brown

In materials from dark igneous rocks or sediments

[BA] Acid Brown

Strongly or extremely acid

[BF] Firm Brown

Strong, apedal subsurface horizon

[BO] Orthic Brown

Other Brown Soils