Hint: The study of soil is important to determine the soil distribution patterns in current and geological periods.
The process of soil formation is termed as Pedogenesis. Various alteration and factors lead to the formation of soil and its various layers, termed as soil horizons. All the layers are different from each other in color, texture, structure etc.
Mostly there are three main horizons-
1. A horizon- this layer is humus-rich and the nutrient, organic matter and biological activity are the highest. It is darker than other layers because of organic matters. It is the topsoil.
2. B horizon- It holds more moisture and is a clay-rich subsoil. It is lighter in color and has less biological activity than the A horizon.
3. C horizon- It is the underlying weathered rock.
Soil formation is influenced by several factors like, parent material, climate, topography, organism, and time.
- Parent material is the initial state of the solid matter making up a soil. They affect the soil formation by their mineral composition, texture, and their stratification. The source of all soil mineral materials is rock, whether igneous, sedimentary or metamorphic. Parent matter, the mineral matter for soil, may contain quartz, calcite, feldspar and mica. Parent material can also get deposited continually by wind, water or volcanos and can be altered from their initial, isolated state.
- Weathering of rocks to form soil is done by a lot of processes like,
1. Physical weathering- breakdown of rocks due to temperature changes, abrasions, frost etc. cause the rocks to break down.
2. Chemical weathering- when minerals in the rock react with water, air or other chemicals, it causes breakdown of the rocks.
3. Biological weathering- cracks in rocks caused by burrowing animals and lichens helps water and air to get inside the rock and helps in breakdown. Plant roots also grow into the cracks making it split.
- The topography may either speed-up or slow down the process. The slope determines the type of vegetation and indicates the amount of rainfall received. These factors change the way soil forms.
Note: Soil properties may also vary depending on how long the soil has been weathered. With time, minerals also get weathered from the soil.