What is the surface accumulation of sand, clay and decayed plant material called?

The surface accumulation of sand, clay, and decayed plant material is referred to as soil. Soil is a complex and dynamic natural resource essential for plant growth and sustaining ecosystems. It originates from the weathering of rocks and the accumulation of organic matter, including decayed plant materials, which enrich the soil and contribute to its fertility.

Soil is made up of various components, including minerals (like sand and clay), organic matter (which includes humus), water, and air. The mixture and proportions of these components can vary widely and influence the soil's characteristics, such as its texture, structure, and nutrient content, thus playing a critical role in agricultural productivity and natural habitats.

While humus is a component of soil made up of decomposed organic matter, it does not encompass the entirety of soil, which also includes mineral particles and other elements. Regolith refers to the layer of loose, heterogeneous material covering solid rock and can include soil, but it is not as specific as the term "soil." Bedrock is the solid rock layer beneath the regolith and soil, and it does not consist of the accumulated organic materials or weathered sediments found in soil layers.