Soil

In addition to the rock particles, the soil contains minerals, organic matter, air and water. The uppermost layer of soil is generally dark and rich in humus. The humus makes the soil fertile.

In clayey soil, particles are smaller in size and tightly packed together. No air is present between particles. So, water can be held in the tiny gaps between the particles of clay. Thus, clay soil has the highest water holding capacity.

(i)- (b)

Soil is one of the most important natural resources. It supports the growth of plants and supplying water and nutrients. It is the home for many living organisms.

(ii)- (c)

The upper layer of the soil is dark in colour as it is rich in humus and minerals. The humus makes the soil fertile.

(iii)-(a),

In sandy soil, particles are quite large and cannot fit closely together. There are large spaces between them that are filled with air. Therefore, water can drain quickly through the spaces between the particles.

(iv)- (e)

The middle layer of the soil has a lesser amount of humus but more of minerals.

(v)-(d)

In clayey soil, particles are smaller in size and tightly packed together. There is no space between the particles for air. Thus, clay soil has the highest water holding capacity.

Soil is formed by the process of weathering. It is a slow process in which the rocks breakdown by the action of air, wind and water. As a result of the process, large rock pieces are converted into small particles. These small particles mix with humus (organic matter) and form soil.

Clayey soil is useful for crops because:

(i) It has very good water retaining capacity.

(ii) It is rich in humus and is fertile.

Therefore, it is suitable for growing cereals like wheat, gram and paddy.

Differences between clayey soil and sandy soil:

Fig. Soil Profile

Time = 40 min ;

Volume of water = 200mL Amount of water

So, Rate of percolation (mL/min)=

=

Therefore, percolation rate of water = 5mL/min

Soil pollution can be prevented by

•Avoid dumping of non-biodegradable wastes in the soil.

•Use of natural pesticides

•Recycling of waste should be done

•Avoid excessive use of pesticides and insecticides

Soil erosion can be done by

•Avoiding overgrazing of grassland

•Preventing cutting of trees

•Using step farming in hilly regions

•Afforestation