The formation of New Zealand soils
The soil classification can be used to trace the formation, or evolution, of New Zealand soils through time. The diagram illustrates major pathways in the evolution of New Zealand soils. In (I) Mineral Parent Materials, (II) Raw Soils develop into (III) Recent Soils. The nature of the parent material then strongly determines the subsequent soil formation pathway (IV). Later, parent material becomes less important, and climate and vegetation become more important controls over the character of the soil that evolves (V). Soils will only proceed the whole way down a soil formation pathway on relatively stable sites. Erosion or additions of fresh sediment may impede, halt or even reverse soil evolution. Many (II) Raw Soils may never develop into (III) Recent Soils or other soils because they occur in environments with continual cycles of erosion or additions of fresh sediment. The pathways shown represent only those likely to have occurred over extensive areas. Other pathways are omitted for clarity. For example, Allophanic Soils may also be formed in quartz, feldspar, and mica parent material, and Ultic Soils may also be formed in mafic or tephra parent materials.