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.
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.
They have relatively stable topsoils with well-developed polyhedral or spheroidal structure.
Soils have low to moderate base saturation. Clay minerals are dominantly mica/illite and vermiculite, with allophane in Allophanic Brown Soils.
Soils contain large, active populations of soil organisms, particularly earthworms.
Soil orders are divided into soil groups based on variation in factors such as drainage status, parent material, chemical and physical properties