Re: Mixing rule for epipedons

The 18-25 cm mixing rule primarily pertains to Mollic and Umbric epipedons. Let's delve into the details:

1. Mollic Epipedon:
- Thickness: 18-25 cm
- Color: Moist chroma < 3.5
- Organic Carbon: Approximately 0.6%
- Base Saturation: 50% (strongly developed)
- Structure: Well-developed
- Characteristics: Rich in organic matter, often found in grassland soils.

2. Umbric Epipedon:
- Meets all criteria of the Mollic epipedon except for base saturation (< 50%).
- Chemically different from Mollic epipedon.
- Typically thinner and lighter in color.
- Commonly found in various soil types.

Remember that these rules are specific to the surface horizons (epipedons) of soils. Other epipedons, such as Ochric, Histic, and Melanic, have their own distinct characteristics and criteria¹. If you encounter soils with different epipedons, their properties may not necessarily align with the 18 cm mixing rule.