Table of Contents
Soil – Soil Types: Sandy – Clayey – Loamy. Soil Profile – Soil Horizon: O horizon, A Horizon, E horizon, B Horizon, C Horizon or Parent rock, R Horizon or Bedrock.
- Soil is the thin top layer on the earth’s crust comprising rock particles mixed with organic matter.
- Pedology is the study of soils in their natural environment. Pedogenesis is the natural process of soil formation that includes a variety of processes such as weathering, leaching, calcification etc..
- The Soil formation is mainly related to the parent rock material, surface relief, climate and natural vegetation.
- The soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called
Soil Types – Sandy-Clayey-Loamy
- The soil is classified on the basis of the proportion of particles of various sizes.
- If soil contains greater proportion of big particles it is called sandy soil.
- If the proportion of fine particles is relatively higher, then it is called clayey soil.
- If the amount of large and fine particles is about the same, then the soil is called
- Water can drain quickly through the spaces between the sand particles. So, sandy soils tend to be light, well aerated and dry.
- Clay particles, being much smaller, pack tightly together, leaving little space for air. Unlike sandy soil, water can be held in the tiny gaps between the particles of clay. So clay soils have little air. But they are heavy as they hold more water than the sandy soils.
- The best topsoil for growing plants is Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the right water holding capacity for the growth of plants.
- Clayey and loamy soils are both suitable for growing cereals like wheat, and gram. Such soils are good at retaining water.
- For paddy, soils rich in clay and organic matter and having a good capacity to retain water are ideal.
- For lentils (masoor) and other pulses, loamy soils, which drain water easily, are required.
- For cotton, sandy loam or loam, which drain water easily and can hold plenty of air, are more suitable.
- A vertical section through different layers of the soil is called the soil profile.
- Each layer differs in feel (texture), colour, depth and chemical composition. These layers are referred to as
- A soil horizon is a layer generally parallel to the soil surface, whose physical characteristics differ from the layers above and beneath.
- Horizons are defined in most cases by obvious physical features, chiefly colour and texture.
- The uppermost horizon is generally dark in colour as it is rich in humus and minerals. The humus makes the soil fertile and provides nutrients to growing plants.
- This layer is generally soft, porous and can retain more water. It is called the topsoil or the A-horizon.
- The next layer has a lesser amount of humus but more of minerals. This layer is generally harder and more compact and is called the B-horizon or the middle layer.
- The third layer is the C-horizon, which is made up of small lumps of rocks with cracks.
- Layers dominated by organic material.
- Some O layers consist of undecomposed or partially decomposed litter (such as leaves, needles, twigs, moss, and lichens).
- They may be on top of either mineral or organic soils.
A Horizon or Surface soil
- It is the part of top soil.
- In this layer, organic matter is mixed with mineral matter.
- It is the layer of mineral soil with the most organic matter accumulation and soil life.
- This layer is depleted of (eluviated of) iron, clay, aluminum, organic compounds, and other soluble constituents.
- When depletion is pronounced, a lighter colored “E” subsurface soil horizon is apparent at the base of the “A” horizon.
- “E” stands for eluviated layer.
- It is the horizon that has been significantly leached of clay, iron, and aluminum oxides, which leaves 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.