Soil is one of the most important natural resources because
(a) It supports the growth of plants by holding the roots firmly and supplying water and nutrients.
(b) It is the home for many organisms.
(c) Soil is essential for agriculture. Agriculture provides food, clothing and shelter for all.
(d) Soil is thus an inseparable part of our life

(a) Humus
(b) Soil Profile
(c) Horizon
(d) Loam
(e) Weathering
(f) Percolation

For making earthen pots, following steps are followed:
(i) Soil is collected from barren lands and place in a tank. It is cleared of all pebbles etc., and soaked for about 8 hours.
(ii) The soil is then kneaded after mixing horse dung in it.
(iii) The kneaded soil is given appropriate shape by placing on the wheel. Then the final shape is given by hand.
(iv) The items are coloured after three days of drying. Then all the items are baked in high temperature.

A gardener often gently digs up the soil around the roots of garden plants or herbs for following reasons
(i) It enables easy root growth.
(ii) For easier percolation of water.
(iii) For aerating the soil enabling air to get into deeper layers of soil.
(iv) For removing the weeds.

Percolation property of any material is linked to its porosity. Different soils have different porosity. Therefore, water percolates differently through different soil.
Percolation rate of water in the soil = \(\frac { volume\quad of\quad water\quad percolated }{ time\quad taken\quad for\quad percolation } \)
Whereas water retaining capacity of a soil is described in terms of the amount of water absorbed by a particular type of soil. High water retaining capacity means higer water absorption.

(a) It is because these substances pollute the soil. They also kill the organisms living in the soil.
(b) Substances which pollute the soil are a number of waste products, chemicals, pesticides, polythene bags and plastics.
(c) Alertness, responsibility and ecofriendly nature

(a) Gravel is the heaviest rock material.
(b) Humus is the lightest soil component which floats on the water surface.
(c) The soil component forms various layer one above the other according to the size of soil particle

The man digging a pit could dig with ease initially because of th~\presence of topsoil and subsoil (mainly comprising of humus and nutrients). But as he digs deeper, he finds it difficult to dig beyond a depth of 5 feet as lower layers are made up of small partially weathered rocks with cracks, crevices and with bedrock which make it hard to dig.

There are three different types of soil
(i) Sandy soil containing sand particles in them.
(ii) Clayey soil contains clay particles with small amount of humus in it. It is a fertile soil.
(iii) Loamy soil is a mixture of sand, clay silt and humus. It is a fertile soil

Clayey soil is useful for the crops because
(i) it has good water retaining capacity.
(ii) it is rich in humus.
(iii) it is fertile in nature.
Crops like wheat and rice can be easily grown in clayey soil.

Given, amount of water = 960 mL
Time taken to percolate = 120 min
The rate of percolation will be
= \(\frac { amount\quad of\quad water(in\quad ml) }{ Percolationtime(inmin) } =\frac { 960ml }{ 120min } =8mL/min\)
Percolation rate = 8 mL/min

Preventions of soil pollution can be done by
(i) using manures instead of synthetic fertilisers.
(ii) using natural pesticides.
(iii) avoiding dumping of polythene and plastics in soil.
(iv) treating industrial waste before releasing it in the soil.
Preventions of soil erosion can be done by
(i) afforestation that is large scale planting in placee cut down forests.
(ii) avoiding overgrazing of grasslands.
(iii) terrace farming and other better farming methods in hilly areas.

Differences between clayey soil and sandy soil are

Clayey soil has an important characteristic. It can retain water and moisture and are rich in humus. Therefore, it is suitable for growing cereals like wheat, gram and paddy.

Soil formation is a slow process which occurs in following two steps
(i) Weathering of rocks is the breakdown of rocks into small particles by the action of air, wind and water.
(ii) These small particles mix with humus (organic matter) and form soil.