Tuesday , July 5 2022

NCERT 7th Class (CBSE) Science: Soil

Question: Soil is constantly formed for weathering of rocks. Why then are we so concerned about soil erosion.

Answer: Soil erosion is the gradual removal or wearing away of the earth’s soil surface by natural agents such as running water, wind, waves and snow. It takes away the fertile topsoil, making the soil infertile and unsuitable for plant growth. Soil erosion is more severe in areas where there are destructive human activities and less or loss of vegetation cover.

The soil covering the surface of the earth has taken millions of years to form. For every 100 to 400 years, soil is formed at a rate of only 1 cm and it takes 3,000 to 12,000 years to build enough soil to produce a suitable land for cultivation. This means that soil once lost would take at least a hundred years to restore. Therefore we are so concerned about soil erosion.

Question: What effect does construction of buildings and roads have on water percolation through the soil? Hence what effect would this have of water table?

Answer: Soil is used for construction of buildings and roads. It effects water percolation through cement and ultimately reduces ground water level known as water label.

Question: Which types of soil is needed for growing wheat, gram, paddy, pulses and cotton.

Answer: Type of soil needed is:

  1. Clayey and loamy soil are both suitable for growing wheat and gram.
  2. Paddy requires soil rich in clay and organic matter with a good capacity to retain water.
  3. For pulses cdals, loamy soils that drain water easily are the best.
  4. For cotton, Sandy – loam (loam that has more sand is best it can hold air but water can drain through it easily.

Question: What is weathering?

Answer: Weathering is the breaking down of huge pieces of rocks into smaller pieces due to the action natural forces such as water, glaciers, wind and roots of plants etc.

Question: Which soil will allow more water to percolate sandy or clayey soil? Why?

Answer: Sand cannot hold much water as water drains quickly through large spaces between the sand particles.

On the other hand clayey soil, which mostly contains clay, water drains through very slowly, sine the particles are very small and tightly packed.

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