The main source of organic matter in soil is

A. water.

B. bacteria.

C. fungi.

D. plants.

Plants are the main source of organic matter in soil. Animals and microorganisms also contribute. Microorganisms, including fungi, bacteria, and single celled protozoans, play an active role in decomposing dead plants and animals. Because organic material releases nutrients when it decays, it contributes to soil fertility. Some bacteria also aid soil fertility in the nitrogen cycle. The bulk of organic matter originates from plants.

The correct answer is bacteria. Bacteria abundant in soil is the main source of its organic matter. This is because bacteria release energy in their systems which causes the soil to be more fertile and more capable of sustaining plant material. Without bacteria general processes of soil formation will not be possible.