Soil Order

Organic Soils [O]

Serving as giant sponges in the landscape, these soils can hold up to 20 times their weight in water.

Organic Soils are formed in the partly decomposed remains of wetland plants (peat) or forest litter. Some mineral material may be present but the soil is dominated by organic matter.

Organic Soil.
Organic Soil.


Organic Soils occur in wetlands in most parts of New Zealand, or under forests that produce acid litter in areas with high precipitation. They cover 1% of New Zealand.

View map View map of Organic soils.

Physical properties

Organic Soils have very low bulk densities, low bearing strength, high shrinkage potential when dried, very low thermal conductivity and high total available-water capacity.

Chemical properties

Organic Soils have high cation exchange capacities, are usually strongly or extremely acid, and nutrient deficiencies are common.

Biological properties

High carbon/nitrogen ratios indicate slow decomposition rates. Many soil organisms are restricted because of anaerobic conditions.

Soil groups

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

[OL] Litter Organic

Thick litter that has accumulated under forest

[OF] Fibric Organic

In peat with plant fibres that are only weakly decomposed

[OM] Mesic Organic

In peat that is moderately decomposed

[OH] Humic Organic

In peat that is strongly decomposed