Maharashtra Board Class 7 Geography Chapter 7 Soils PDF Download

Soils

Let's recall.

What are the different constituents of soil?

From where do the abiotic factors become available for soil formation?

On which factors does the variety in the soil depend?

While answering the questions above, you must have gathered some information about soil and realized some of its characteristics. Let us consider the soil in more detail.

The parent rock, the climate of the region, the biotic material, the slope of the land and time are factors that influence soil formation.

Factors Necessary For Soil Formation

Parent Rock

Remember that the parent rock in a region is an important factor in soil formation. Depending on the hardness of the rock and the climate of the region, the rock gets weathered. The rock turns into powdery material which further turns into earthy material. For example, the basalt rock of the Deccan Plateau in Maharashtra turns into black soil after weathering. This soil is also referred to as 'regur' soil. Rocks like granite or gneiss in South India give rise to red soil.

Teacher's Note

Soil takes thousands of years to form. In India, the Deccan Plateau's black soil (regur) is made from basalt rock weathering over long time.

Exam Trick

Remember: Parent rock + weathering + time = soil. Just like how a stone in a river becomes smooth over many years, parent rock becomes soil over thousands of years.

Points To Remember

Parent rock is the source material for soil formation.
Weathering breaks down rocks into powdery material.
Different rocks make different types of soils.
Basalt rock makes black soil (regur).
Granite and gneiss rocks make red soil.

Regional Climate

This is also an important factor influencing soil formation. Weathering of the rock is the first step in the process of soil formation. The process of weathering depends on the climate of the region. The climate decides the intensity of weathering. That is why one and the same type of rock gives rise to different types of soils when the rock is exposed to different climates. In the dry climate of Deccan Plateau, weathering of basalt leads to the formation of black soil whereas in the humid climate of the Western Sahyadris the leaching of the same basalt rock leads to the formation of lateritic soil.

Teacher's Note

Climate changes how rocks break down. In wet areas, the same rock becomes laterite soil. In dry areas, it becomes black soil.

Exam Trick

Remember: Same rock + dry climate = black soil. Same rock + wet climate = laterite soil. Climate is the key difference!

Points To Remember

Climate affects how fast rocks weather.
Dry climate makes black soil from basalt.
Wet climate makes laterite soil from basalt.
The same rock makes different soils in different climates.
Weathering speed depends on climate.

Biotic Material

The weathering of rocks turns them into powdery material but this powdery material is not soil. To turn such powdery material into soil, it is necessary that biotic material gets mixed into it. The biotic material comes from the decomposition of the remains of the plants and animals in that region. The vegetal litters, roots of plants, remains of animals, etc. get decomposed due to water. Microorganisms, and certain other organisms help decompose the dead remains of organic materials. The biotic material thus produced gets mixed into the soils and is called 'humus'. If the proportion of humus in the soil is greater, the soils become fertile.

The process of decomposition by living organisms takes place continuously. Now-a-days production of vermicompost is undertaken on a large scale. Try to understand the process of producing vermicompost or compost. Production of compost needs sufficient period of time and elements like organic waste, water, heat etc.

Teacher's Note

Humus is made from dead plants and animals. Worms in your garden make vermicompost, which is like homemade soil nutrient.

Exam Trick

Remember: Dead plants and animals = humus. Humus = fertile soil. Like how kitchen waste becomes compost, soil needs organic matter to be healthy.

Points To Remember

Biotic material comes from dead plants and animals.
Decomposition makes humus.
Humus makes soil fertile.
Microorganisms help break down dead matter.
More humus means better soil for growing crops.

Time

Soil formation is a natural and slow process. It needs a very long period of time. To form a 2.5 cm thick layer of top soil, it takes thousands of years. From this you may understand that soils are invaluable. In the region of high rainfall and higher temperatures, the process of soil formation is faster. Comparatively, in regions of low temperatures and low rainfall soil formation takes more time.

Teacher's Note

It takes 1000 years to make just 2.5 cm of soil. This shows soil is a precious resource that we must protect and not waste.

Exam Trick

Remember: 2.5 cm soil = 1000 years. Tropical areas make soil faster because of heat and rain. Cold deserts make soil very slowly.

Points To Remember

Soil formation takes thousands of years.
2.5 cm of soil takes about 1000 years to form.
High rainfall and temperature speed up soil formation.
Cold and dry regions take longer to form soil.
Soils are invaluable and must be protected.

Humans use the soil gifted by nature as a resource. It is mainly used for agricultural purpose. For getting higher production, different types of chemical fertilizers, insecticides are used profusely. However, this leads to the degradation of soils.

Try This

Take three flower pots of the same size

Keep one pot empty. Fill the second pot with water after closing the hole at the bottom and third pot with soil.

Put a few seeds in all of them. (You may use aserio, peas, gram, fenugreek, wheat, green gram, coriander seeds, etc.)

Keep all the three pots in the sun and water the empty pot and the soil-filled pot for 4-5 days. Observe and answer the following.

What happened to the seeds put in the empty pot and the pot filled with water?

An important component of the living world on the earth is 'plants'. For the production and growth of plants, soil is indispensable. They provide support to plants. Vegetation is abundant in the regions that have fertile soils, e.g., the equatorial regions. However, in the areas where the soils are not fertile, vegetation is scanty, e.g., in deserts. And where there is a shortage of soil, vegetation is not seen, e.g., in the polar areas.

Though favourable climate, availability of abundant water and sunlight are necessary for the growth of a plant, these alone are not sufficient. Fertile soils favour plant growth.

Always Remember

Earth doesn't mean soil:

Soil contains the powdered form of weathered rock, partially or completely decomposed organic material and innumerable microorganisms. Interactions between biotic and abiotic components in the soil go on continuously. Plants get nutrients required for their growth from the soils. Soil is a complete ecosystem. Earth is also a substance. The potter uses it as raw material. A farmer uses soil as an ecosystem.

Teacher's Note

Soil is not just earth. Soil is alive with organisms and nutrients. Earth is just a material, but soil is a complete living system.

Exam Trick

Remember: Earth = dead material for pots. Soil = living ecosystem with plants, worms, and nutrients. Two different things!

Points To Remember

Soil has weathered rock, organic matter, and living organisms.
Soil is a complete ecosystem.
Earth and soil are not the same thing.
Potters use earth as raw material.
Farmers use soil as an ecosystem.

What happened to the seeds put in the pot filled with soil?

What do you learn from this?

Geographical Explanation

Why do equatorial regions have fertile soils?

Why is the vegetation sparse in deserts?

When man realized that sowing of seeds in the soil leads to the growth of plants and yields crops, he started using soil as a resource. Gradually, he realized that the fertile soils along the river beds give higher yields. Hence he settled in the valleys and started living there in groups. This led to the rise of ancient river valley civilizations, e.g., the Indus civilization.

For the growing population, man started producing greater amount of food crops. He realized that crop production and prosperity in agriculture mainly depends on the fertility of soil and the optimum availability of water. Hence, there emerged competition among people to discover fertile lands and settle there. Later, for getting richer harvests he made efforts to increase the fertility of soils. In the process, use of different fertilizers became a practice, which led to record agricultural productions.

Food crops, fruits and flowers are produced according to the type of soils. Food crops like jowar and bajra are produced in the regur soils of Maharashtra Plateau while soils in Konkan, Kerala, Tamilnadu and Karnataka region produce rice. In Madhya Pradesh, potato is cultivated in regions where the soils are well drained. The local agricultural produce determines the staple diet of the people.

The regions where soils are not arable need to fulfil their food requirements through import. For example, countries like Saudi Arabia, Qatar, Oman, etc. fulfil their requirements by importing food from China, India and the USA.

The regions where soils are fertile can be self-reliant as far as the food production is concerned. Hence, human settlements get concentrated in such areas. Agro-based industries flourish in these areas at a later date. For example, sugar factories develop in the sugarcane producing areas; fruit processing industries develop in the areas of fruit production, etc. These regions later show the signs of development.

Teacher's Note

Good soil brought people together to settle in ancient times. The Indus Valley Civilization grew because of fertile river valley soils.

Exam Trick

Remember: Fertile soil = civilization develops. People settle near good soil to grow food. This is why all old civilizations started near rivers with good soil.

Points To Remember

Different soils produce different crops.
Fertile soils help civilizations grow.
Black soil (regur) grows jowar and bajra.
Areas with no good soil must import food.
Good soil brings development and industries.

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