12. Constituents of soil :
a. Soil has constituents of both plane and animal origin. There constituents are called organic costituents.
b. Constituents of plant origin include bacteria, algae, fungi, decomposed leaves of plants, etc.
c. Constituents of animal origin constituttue protozoa,worms, insects, shells and decomposed remains of dead animals.
13. Soil erosion :
a. The removal of top fertile layer of the soil from the soil surface is called soil erosion.
b. Soil is eroded by rainwater falling on it and by east currents of water flowing on it .
c. Soil is also eroded by rust of winds.
d. Soil must be kept covered to prevent soil erosion. Growing grass and the cross on the land, cover the soil.
e. Trees planted on the land also provide the cover.
f. Soil erosion can be reducee by arranging the soil horizontally across the lines of slopes as erosion of soil depends upon the slope.
g. Construction of bunds to stop the flowing water also prevents the soil erosion.
14. Soil Conservation :
a. Arresting soil erosion to conserve the soil is called soil conservation.
b. The government has set up soil conservation department at every district place. One can get information about how to reduce soil erosion at this place.
15. Social forestry :
a. Planting of the trees on the borders of fields on the sides of roads and railway tracks and on the banks of rivers and streams is called social forestry.
b. The government of India, in the year 1976, started social forestry projects for the benefit of the people.
c. The project motivated the people to start planting of trees in all possible places.
d. Tip project encourages small farmers and adivasis to plant trees. It provides financial assistance to them for this purpose.
16. Soil pollution :
a. A disturbance in the natural balance of various constituents of soil is called soil pollution.
b. Chemical fertilizers, pesticides, industria effluents, etc. Pollute the soil.
c. Crops do not grow well on polluted soil.
d. Soil pollution can be prevented by using organic fertilizers instead of chemical fertilizers.
e. Overuse of fertilizers and pesticides should also be avoided for the prevention of the soil pollution.
17. Soil testing :
a. Soil testing is done to find out the quality of the soil.
b. Soil testing helps up to find out the colour, texture and the constituents of organic matter in the soil.
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