A soil profile typically consists of three to five different layers, each with a distinct set of characteristics. A letter system is used to label these layers, known as horizons. The A horizon is the uppermost layer, followed by the B horizon, and the C horizon is the final layer. The O and R horizons may also be present in certain soils.
There are two types of soil horizons:
- Organic horizons:The capital letter O marks organic horizons that form from plant and animal matter and lie over mineral horizons. The upper Oi horizon contains decomposing organic matter that you can easily recognize by eyes, such as leaves or twigs. The lower Oa horizon contains humus, which has broken down beyond recognition.
- Mineral horizons: There are four main mineral horizons: A, E, B, C
Soil Profile Diagram
Types of Soil Profile
A soil horizon is a distinct layer parallel to the soil surface that differs in various physical, chemical, and biological characteristics of the soil. The soil profile expands from the soil surface to the parent rock material.
Four major components of soil include:
- Inorganic minerals
- Organic matter
- Water and air
- Living matter (microorganisms)
Layers of Soil
O-Horizon
- The O-Horizon soil contains organic components that can degrade, such as dried leaves, tiny boulders, downed trees, and other organic stuff.
- It contains about 20 and 30 per cent organic materials.
- Due to the presence of organic debris, the soil is often black or dark brown in colour.
- It is most noticeable in forested areas where there is an accumulation of tree debris.
A-Horizon
- The A-Horizon Layer, also known as the Humus Layer, is made up of organic material.
- A surface horizon called the A horizon is primarily composed of minerals (sand, silt, and clay) with trace quantities of organic materials.
- Dark decomposed materials known as humus make up the topmost layer of soil.
- Humus enriches the soil with nutrients, making it more fruitful. It also keeps the soil alive.
- This horizon is mostly the surface layer of many grasslands and agricultural soils.
- This layer is soft and may retain more water than any other layer because it boosts the soil’s water retention capacity.
- This layer contains many living creatures, such as beetles and worms.
E horizon
- “E” stands for eluviated layer.
- Significant leaching of clay, iron, and aluminum oxides results in the horizon with a concentration of resistant minerals, such as quartz, in the sand and silt sizes.
- These are present only in older, well-developed soils, and generally occur between the A and B horizons.
B Horizon or Subsoil
- It is subsurface layer reflecting chemical or physical alteration of parent material.
- This layer accumulates all the leached minerals from A and E horizon.
- Thus iron, clay, aluminum and organic compounds accumulate in this horizon [illuviation (opposite of eluviation)].
C Horizon or Parent rock
- Weathered parent material accumulates in this layer, i.e. the parent material in sedimentary deposits.
- It is a layer of large unbroken rocks.
- This layer may accumulate the more soluble compounds (inorganic material).
R Horizon or Bedrock
- This layer denotes the layer of partially weathered bedrock at the base of the soil profile.
- Unlike the above layers, R horizons largely comprise continuous masses of hard rock.
- Soils formed in situ will exhibit strong similarities to this bedrock layer.
- These areas of bedrock are under 50 feet of the other profiles.
Significance
- The study of the soil profile is significant in agriculture sciences because the land use pattern can be determined.
- Land capability classification is based on the study of soil profile & horizon.
Frequently Asked Questions related to soil profiles:
Ques 1. What is a soil profile?
Ans. A soil profile is a vertical section of the soil that shows the different layers or horizons of soil. It provides a visual representation of the soil’s composition, structure, and characteristics from the surface down to the underlying bedrock or parent material.
Ques 2. How is a soil profile formed?
Ans. The process of weathering and soil development forms a soil profile over time. Factors such as climate, vegetation, topography, and parent material influence the formation of different soil horizons, resulting in a distinct layering pattern.
Ques 3. What information can be obtained from studying a soil profile?
Ans. Studying a soil profile can provide valuable information about the soil’s fertility, nutrient content, drainage capabilities, and physical properties. It helps determine soil suitability for agricultural purposes, land management decisions, and understanding soil health and ecosystem dynamics.
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