What is the name of the rich black organic material in some soils?

The rich black organic material found in some soils is known as humus. Humus is the result of the decomposition of plant and animal matter, contributing significantly to soil fertility and structure. It enhances the soil’s ability to retain moisture and nutrients, making it essential for healthy plant growth. In addition to its dark color, which comes from the high organic content, humus improves soil aeration and promotes the activity of beneficial microorganisms.

While other choices represent different components of soil—such as clay, which consists of fine particles that can compact but may limit drainage; silt, which is made up of medium-sized particles offering good nutrient retention and drainage; and loam, a mixture of sand, silt, and clay that creates a balanced soil structure—humus is specifically the decomposed organic material that is crucial for enriching the soil and supporting ecosystems.