Histic horizon (WRB)

An histic horizon consists of organic material that:

• is saturated with water for 30 consecutive days or more in most years (unless drained)

and :

• has a thickness of 10 cm or more. If the layer with organic material is less than 20 cm thick, the upper 20 cm of the soil after mixing, or if continuous rock is present within 20 cm depth, the entire soil above after mixing, must contain 20 percent or more organic carbon

Relationships with some other diagnostic horizons

• the folic horizon has similar characteristics to the histic horizon; however, the folic horizon is saturated with water for less than one month in most years. Moreover, the composition of the histic horizon is generally different from that of the folic horizon as the vegetative cover is often different
• the lower limit of organic carbon content, varying from 12 percent (20 percent organic matter) to 18 percent organic carbon (30 percent organic matter), sets the histic horizon apart from mollic or umbric horizons, which have these contents as upper limits.
• histic horizons with less than 25 percent organic carbon may have andic or vitric properties.

Classification hints

When a soil displays an histic horizon, it may be related to one of the following Reference soil groups :

• Andosol
• Fluvisol
• Gleysol
• Histosol
• Podzol
• Solonchak