NCERT Class 7 Science Chapter 9 - Soil

Chapter 9 - Soil

Question and Answers
Question 1: In addition to the rock particles, the soil contains
minerals, organic matter, air and water.
 
Question 2: The water holding capacity is the highest in clayey soil.
 
Question 3: Explain how soil is formed.
Answer:
Soil is formed due to the weathering of rocks. Weathering is a process in which physical breakdown and chemical decomposition of minerals takes place primarily by wind, water and climatic changes. In the weathering, the rocks are converted to small pieces, which changes to soil particles to form a layer of soil.
 
Question 4: How is clayey soil useful for crops?
Answer:

*It has excellent water holding capacity
*Clayey soil is rich in organic matter
*Clayey and loamy soils are suitable for growing cereals like wheat
*Water holding-capacity of clayey soil supports the growth of crops like paddy which require more water to grow
 
Question 5: List the differences between clayey soil and sandy soil.
Answer:

Clayey Soil
* Particles are finer
* Particles are tightly packed
* Holds a good amount of water
* It is heavy in weight
* Rich in humus and organic nutrients
* Very little air is trapped between the particles

Sandy Soil
* Particles are larger
* Particles are loosely packed
* Water holding capacity is low
* It is light in weight
* Not rich in humus and organic nutrients
* More air is trapped between the particles
 
Question 6: Sketch the cross-section of soil and label the various layers.
Answer:

Question 7: Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Answer:

Amount of water = 200 mL
Percolation time = 40 minutes
Percolation rate = ?
Percolation rate = (amount of water (mL))/(percolation time (min) = (200 mL)/(40 min)
= 5 mL/min
 
Question 8: Explain how soil pollution and soil erosion could be prevented
Answer:
Soil pollution can be prevented by following these measures -
*By reducing the use of plastics, we can reduce soil pollution.
*By controlling the use of chemical fertilizers and pesticides, we can control soil pollution.
Soil erosion can be reduced by these following steps -
*Planting more and more trees will result in the reduction of soil erosion.
*By stopping deforestation and avoiding overgrazing of animals.

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