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CBSE Class 7 Chemistry Notes- Chapter 4 Soil

A soil profile is a vertical section through which different sections of the soil can be seen. The different layers are also known as Horizons.
A- Horizon

  • The uppermost layer of the soil. Also called top soil
  • Generally dark in colour
  • Rich In humus (rotting dead matter in the soil) and minerals
  • Soft, porous and retains more water
  • Fertile and provides nutrients to growing plants

B- Horizon

  • The layer below A- Horizon
  • Less amount of humus but more minerals
  • Harder and compact
  • Also called the middle layer

C- Horizon

  • The layer below B- Horizon
  • Has small lumps of rocks
  • Has cracks and crevices


  • Below the C-Horizon
  • Hardest layer
  • Comprised of rocks

Soil contains sand and clay. The proportion of particles determine the kind of soil.
Sandy soil

  • Contains more of the big particles
  • Sandy soil is well aerated
  • Water can drain through it quickly

Clayey soil

  • Contains more of the fine particles
  • There is not much air
  • It is heavy as it can hold more water than sandy soil

Loamy soil

  • Same amount of both large and small particles
  • Best for growth of plants

1. Percolation rate of water
     Percolation rate is the gradual movement of water through the soil.
            Percolation rate= Amount of water(mL) / Percolation time(min)
2. Moisture in soil
     It is the amount of water in the soil.
3. Absorption of water
The capacity to absorb water by the soil is called absorption capacity. Different soils have    absorption capacity.

  • Wheat is grown in clayey or loamy soil
  • Paddy is grown in clayey soil
  • Pulses are grown in loamy soil
  • Cotton is grown in sandy loam or loamy soil

Removal of top soil by wind, water or ice is called soil erosion. This degrades the soil quality.

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