Which Materials Make up the A Horizon in Soil

Which Materials Make up the A Horizon in Soil

Soil Profile
Due to the physical, chemical, and biological activities that take place during soil formation, well-developed layers of soil are formed, one below the other. Typically, four distinct soil layers can be seen. These layers are referred to as horizons.
A vertical section of soil from the ground surface to the parent rock that shows the different layers of soil or the horizons is called soil profile.

1. A horizon or topsoil is the uppermost layer of soil. It consists of fine particles. It is rich in humus and therefore dark in colour. It is soft, porous, and can hold water. O horizon lies just above the topsoil and is rich in organic matter.
2. B horizon or subsoil is rich in minerals that seep’down along with water. It also contains
   compactly packed fine particles of soil.
3. C horizon contains partly weathered pieces of rock. It is usually characterized by cracks and crevices. It is very difficult to dig beyond this layer.
4. R horizon or Bedrock is the lowermost layer and mainly consists of the parent rock. The properties of this rock greatly determine the composition of the soil.

Composition of soil
The main constituents of soil are water, sand, clay, silt, pebbles, and humus. Table gives the particle size of some of these constituents. The differences in the proportion of these constituents leads to the formation of different kinds of soils.
Table: Particle size of constituents

Activity
Aim: To separate the various constituents of a soil sample into different layers Materials needed: Soil sample, beaker, glass jar, and water
Method:
1. Take two-three handfuls of soil from a nearby garden. Mix it with a glass of water in a beaker.
2. Stir the mixture well and pour it into a glass jar.
3. Allow it to stand undisturbed for one or two hours. Observe the jar.
Observation: Formation of different layers of soil can be observed.
Conclusion: Soil is made up of various constituents that occur in layers.