Which characteristics define a mollic horizon?

A mollic horizon is characterized by a minimum depth and a significant organic carbon content. This type of horizon typically forms in grassland ecosystems and is recognized for being dark in color and rich in organic matter, which contributes to its high fertility. The organic carbon content must exceed 0.6% and the horizon must be at least 25 cm thick. These criteria are essential for classifying a horizon as mollic, distinguishing it from other soil horizons that may have different compositions and properties.

While high clay content, presence of iron oxides, and low bulk density are important soil characteristics, they do not specifically define a mollic horizon. A mollic horizon can vary in clay content and is not necessarily defined by iron oxide presence or bulk density. Understanding these defining features helps in identifying and classifying soils accurately within the context of soil morphology and classification systems.