Answer: O and A horizon
A soil horizon refers to the different layers of soil, which develop parallel to the land surface. These distinct layers are formed due to physical, chemical and biological processes occurring in them. Each horizon can be distinguished from other on the basis, of texture, composition and depth of soil where they are formed.
The soil layers that comprise the topsoil are O and A horizon.
O or Organic Horizon: This soil layer or horizon receives the maximum of the plant and animal litter, which remains in the form of partially decomposed organic matter.
A or Surface Horizon: This layer of soil consists of fine particles of minerals obtained by the weathering process of parent rock and organic matter from organic horizon also get mixed with it. This layer of soil is highly fertile for plant growth.
