Which of the following is not a way that humus affects the properties of soil?

a. Humus expands with increased moisture levels

b. Humus increases the movement of water and air in soil.

c. Humus decreases the porosity of soil

d. Humus acts as a basis for soil life

The answer is C. Humus do not decrease soil porosity instead it increases its porosity. It plays a major function in the determination of soil fertility and it is what determines the life of the soil. Humus makes sure that water, air and nutrients are circulated in the soil properly to maintain balance in the soil.