Roots, although underground, possess living cells that require oxygen for respiration and production of energy. They absorb oxygen that is present in the spaces between soil particles. But in waterlogged soils, water occupies the spaces between soil particles and pushes the oxygen out into the atmosphere. Thus, roots are deprived of oxygen and this affects root and plant growth.

Take a funnel. Take a filter paper, fold and place it as shown in the figure. Weigh 50 gm of dry, powdered soil and pour it into the funnel. Measure a certain amount of water in a measuring cylinder and pour it drop by drop on the soil. Do not allow the water to fall at one spot. Pour water all over the soil.

Keep pouring water till it starts dipping. Subtract the amount of water left in the measuring cylinder from the amount you started with. This is the amount of water retained by soil.
Record it in this manner:
Weight of soil = 50 mg
Initial volume of water = U mL
Final volume of water = V mL
Volume absorbed by the soil = (U- V) mL
Weight of water absorbed by the soil = (U - V) gm
because weight of 1 mL of water = 1 gm
Percentage of water absorbed = \(\frac { U-V }{ 50 } \times 100\)
Repeat this activity with different samples of soil. You observe that different soils have different absorbing capacity of water.

The upper crust of the earth, which is capable of supporting vegetation is called soil. We usually see the surface of the soil. The sides of trench sides of a hill or steep river banks are clearly visible different zones or layers. The side-view of soil zones or layer is known as soil profile.
The upper most layer of the soil is called the A-horizon or top soil. It absorbs maximum water. The top soil consists of soil particles, minerals, water and humus. The decomposed organic matter (decayed plant and animal) remains forms a spongy and brownish or blackish material known as humus. The humus makes the soil very fertile. It also increases water holding capacity of the soil. Worms, insects, algae and fungi are found in the top soil. You will also find roots of plants in this layer. Plants get essential nutrients from the top through roots.
The second layer, called B-horizon, is more compact and harder than the top soil. It consists of sand, silt and clay. This layer contains very little organic matter. It is rich in soluble minerals and iron oxides.
The third zone, called C-horizon, consists of weathered rock. It is made up of small lumps of rocks with cracks and crevices. Below the C-horizon is found the bedrock.

The removal of land surface or the top soilby water, wind or ice is known as soil erosion.
Plant roots firmly bind the soil. In the absence of plants, soil become loose. So it can be easily moved by wind and flowing water.
For preventing soil erosion, deforestation and cutting of trees should be prevented and efforts should be made to increase the green area. Erosion of soil is more severe in areas of little or no surface vegetation, such as deserts or barren lands.

The moisture content of the soil can be calculated by the formula as follows
= \(\frac { mass\quad of\quad water\quad in\quad soil }{ original\quad mass\quad of\quad soil } \times 100\)
Given, Original mass of soil = 200 g
Mass of soil after drying = 170 g
Then mass of water in soil will
= 200 - 170 = 30 g
The percentage of water in soil will be
\(\frac { 30g }{ 200g } \times 100=15%\)
 

Raw soil differs from baked soil. The raw soil is white or dull blackish coloured soil. It contains water and air in it and can be moulded.
Baked soil is the heated raw soil which lost its water molecule due to heating and becomes red. Once the soil gets heated, it cannot be moulded into other form. Clay soil is used for making matkas, toys, pots, etc. The soil is kneaded along with horse dung to make best quality of raw clay soil. This kneaded soil is then placed on the wheel and appropriate shape is given. The final shape of the material is given with hands. The pots and matkas are then kept for drying for three days. These items are baked at high temperature after drying in air and then coloured.

Ans. Yes, soil erosion does not occur easily where the land is covered by vegetation (trees and other plants). It occurs easily in those areas of land which are not covered by vegetation (trees and other plants) or have very little vegetation. If there is vegetation on land,
(i) then the roots of vegetation growing in the soil bind the particles of topsoil firmly. Due to this, the blowing wind and flowing rainwater are not able to carry away topsoil and hence soil erosion does not occur.
(ii) then much of the falling rain hits the trees and plants before it hits the soil. In this way, the cover of vegetation softens the effect of heavy rains on the soil

The borewells have to be dug very deep to get water as compared to those in villages because
(i) excessive use of water depletes the groundwater.
(ii) towns and cities have asphalted roads and vast areas of soil are concreted. As a result, rainwater cannot percolate to recharge groundwater and the groundwater level further decreases. Villages have larger areas of open soil surface and fewer asphalted roads and concrete surfaces.
Thus, larger soil surface area is available for rainwater to percolate into the soil easily and recharge the groundwater. As a result, even shallow borewells yield
water.

The contamination of soil with waste materials especially used polythene bags and plastics, pesticides, fertilisers, acid rain industrial chemical wastes, etc., is called soil pollution
Pesticides are the poisonous chemical substances which are sprayed on standing crops to save them from the harmful insects and diseases. Some of these pesticides also mix up with the soil in the fields and pollute it. The grains, fruits and vegetables grown in this polluted soil contain pesticides. When we eat such contaminated grains, fruits or vegetables, the pesticides present in them damage our health also.

Strong wind and rain can cause soil erosion from the barren land. This can be shown by performing an activity.
Take a wooden block and place some soil or sand on it. Keep an ice-cube tray at one end of the wooden black. Take a small battery-operated fan or hair dryer and hold it at the other end of the black near sand so that it blows the sand into the tray.
We will observe that when the fan blows it causes sand or soil particles to move and these get land in the various compartment of the ice-cube tray. This activity shows that the wind blows the soil on a barren land and may cause soil erosion.