Will give  brainliest , the dark portion of the soil created by the decay of organic matters? is called?

The answer is; Humus  

Humus is found in the topmost layer of the soil where there is decomposing organic matter. This layer of soil has a characteristic color of dark brown to black. This layer of soil also teems with microbial activity and organisms such as earthworms, fungi, and arthropods which  are  significant in the decomposition of the dead organic matter.

the answer would be a