mollic

Mollic is a term used in soil science to describe a mineral soil horizon that is dark in color and rich in organic matter, with high base saturation. It is a diagnostic horizon that plays a key role in identifying Mollisols, the soil order named after this feature. The name derives from Latin mollis, meaning soft, reflecting the horizon’s pliable, well-structured character and its ease of cultivation when excavated or tilled.

Characteristics of a mollic horizon include its dark hue, substantial organic matter content, and strong agricultural fertility. It is typically near the soil surface and forms in settings with limited leaching, good drainage, and persistent vegetation that contributes litter and humus, often grasses. Mollic horizons often exhibit a relatively low degree of weathering and a chunky or granular soil structure that supports root proliferation and easy tillage.

Formation and distribution: mollic horizons develop under grass-dominated ecosystems, such as prairies or steppes, where continuous organic input from vegetation accumulates over long periods. They are common in temperate regions and are widespread in parts of North America, Europe, and Asia, with extensive occurrences in the great grassland regions of the world. These horizons contribute to the high natural fertility that makes Mollisols a prominent agricultural soil type.

Relation to soil taxonomy: the mollic horizon is one of the principal diagnostic horizons in soil classification. Its presence distinguishes Mollisols from other soil orders, such as Alfisols or Ultisols, by signaling a dark, organic-rich, base-rich surface horizon with limited illuvial clay accumulation.