Factors of Soil Formation
Powdered rock is not yet soil. Decayed organic matter must mix in and that takes a very long time.
Soil formation depends on parent rock, regional climate, biotic material (humus), slope of land and time.
Key idea 1 : Parent rock and climate — Depending on rock hardness and climate the rock weathers to powder and then earthy matter. Basalt of Maharashtra’s plateau gives black (regur) soil; granite and gneiss of South India give red soil. Climate decides weathering intensity. So the same basalt gives black soil in the dry Deccan and, leached in the humid Western Sahyadris, lateritic soil.
Key idea 2 : Biotic material (humus) — Powdered rock is not soil. Biotic material must mix in. Remains of plants and animals, litter and roots decay due to water and microorganisms. The material formed mixes into soil and is called humus. More humus makes soil fertile. Vermicompost and compost are produced the same way.
Key idea 3 : Time — Soil formation is a natural slow process. A 2.5 cm top layer takes thousands of years so soil is invaluable. In regions of high rainfall and temperature it is faster; in low temperature and rainfall it takes longer. Earth and soil are not the same; soil has powdered rock, decayed matter and countless microorganisms and is a whole ecosystem.
- Easy : Basalt gives which soil? — Black (regur).
- Medium : Humus is? — Decayed organic matter.
- Exam-type : Time for 2.5 cm layer? — Thousands of years.
In the figure: From rock to soil.
Rock + climate + humus + time = soil.
Rock powder is not soil until humus mixes in.
Memory clue: Rock-climate-life-slope-time: five factors.
Spot the difference
| Rock | Climate | Soil |
|---|---|---|
| Basalt | Dry (Deccan) | Black |
| Basalt | Humid (W. Sahyadri) | Lateritic |
| Granite, gneiss | South India | Red |
Practice questions
- 1What are the factors of soil formation?
- 2How does parent rock affect soil?
- 3Why does the same rock give different soils?
- 4What is humus?
- 5Why is rock powder not soil?
- 6How long does soil take to form?
- 7In which climate is soil formation faster?
- 8State the difference between earth and soil.
Show answers (try them yourself first)
- 1Parent rock, climate, biotic matter, slope, time.
- 2Rock type sets soil colour and properties.
- 3Because weathering differs with climate.
- 4Decayed organic matter.
- 5It lacks mixed biotic matter.
- 6Thousands of years (for 2.5 cm).
- 7High rainfall and temperature.
- 8Soil is an ecosystem; earth is a raw material.
Soil, Plants and Human Life
Seeds kept only in water do not grow as they do in soil, so soil provides something needed for growth.
Soil gives plants support and nutrients. So fertile regions have abundant vegetation and human settlements and farming concentrate there.
Key idea 1 : Soil and plants — Soil is essential for plant growth and gives support. Equatorial regions have fertile soil and abundant vegetation. Deserts have infertile soil and sparse vegetation; polar areas lack soil and show no vegetation. Favourable climate, water and sunlight are not enough; fertile soil is also needed.
Key idea 2 : Soil and humans — When humans learnt that sown seed gives crops they used soil as a resource. Learning that fertile river-bed soil yields more, they settled in valleys in groups, and ancient river-valley civilisations like the Indus arose. For a growing population, the search for fertile land, use of fertilisers and record production followed.
Key idea 3 : Crops, diet and development — Crops depend on soil. Jowar and bajra grow on regur soils of Maharashtra’s plateau, rice in Konkan, Kerala, Tamil Nadu and Karnataka, potato in well-drained soils of Madhya Pradesh. Local produce sets the staple diet. Regions with poor soil must import food; Saudi Arabia, Qatar and Oman import from China, India and the USA. Settlements gather in fertile areas and agro-based industries follow, e.g. sugar factories in cane regions.
- Easy : Sparse vegetation in deserts? — Infertile soil.
- Medium : Indus civilisation arose in? — A river valley.
- Exam-type : Crops of regur soil? — Jowar, bajra.
In the figure: Fertile soil: base of development.
As per the textbook fertile river soil and enough water led humans to settle in river valleys and ancient river-valley civilisations like the Indus arose. (as per the textbook)
Fertile soil → crop → settlement → industry.
Good climate alone is not enough without fertile soil.
Memory clue: Soil = food = settlement.
Spot the difference
| Region | Soil | Vegetation |
|---|---|---|
| Equatorial | Fertile | Abundant |
| Desert | Infertile | Sparse |
| Polar | Lacking | None |
Practice questions
- 1Why is soil necessary for plants?
- 2Why is soil fertile in equatorial regions?
- 3Why is vegetation sparse in deserts?
- 4How did ancient river-valley civilisations arise?
- 5Which crops depend on soil? Give examples.
- 6Why do some countries import food?
- 7Why do agro-based industries grow in fertile areas?
- 8Why did fertiliser use begin?
Show answers (try them yourself first)
- 1It gives support and nutrients.
- 2High heat and rain speed up soil formation and decay of organic matter.
- 3Soil is infertile.
- 4Fertile soil and water drew settlers.
- 5Jowar-bajra regur; rice Konkan; potato M.P.
- 6Their soil cannot grow food.
- 7Raw material is available nearby.
- 8To raise production.
Soil Types of Maharashtra
Soil in our village looks different from Konkan’s soil. Maharashtra has five main soil types.
On colour, texture, formation and layer thickness Maharashtra’s soil has five types: coarse, regur (black), laterite, coastal alluvial and yellow-brown.
Key idea 1 : Coarse and regur soil — Coarse soil forms by weathering and low rain; found on the hilltops of the western plateau, e.g. Ajanta, Balaghat and Mahadeo hills; humus is negligible. Regur (black) soil is found in medium-rainfall river valleys and alluvial plains: dark black in the western Deccan and medium black in the east (Vidarbha); though black, its organic content is low.
Key idea 2 : Laterite and coastal alluvial — Laterite soil is found in Konkan west of the Sahyadris and in east Vidarbha. In very heavy rain eroded rock washes away and parent rock lies bare; its iron reacts with air’s oxygen giving a reddish-orange colour. Konkan rivers are short and fast so alluvium settles at their mouths; coastal alluvial soil is found around the Panvel-Uran coast and Dharamtar creek.
Key idea 3 : Yellow-brown soil and GI tag — Yellow-brown soil lies in areas of extreme rain such as Chandrapur, east Bhandara and parts of the Sahyadris. It is not very fertile and less useful for farming. Some soils suit certain crops and that crop becomes the area’s speciality; such crops get the Geographical Indication (GI) status. Examples: Haapus mango of Sindhudurg, custard apple from Beed, oranges of Nagpur.
- Easy : Most extensive soil? — Regur (black).
- Medium : Reddish iron-rich soil of Konkan? — Laterite.
- Exam-type : Example of GI? — Nagpur oranges.
In the figure: Five soil types.
As per the textbook Haapus mango of Sindhudurg, custard apple of Beed district and Nagpur oranges have received the GI status. (as per the textbook)
Black = medium rain; laterite = very heavy rain.
Black soil is not rich in organic matter; it has little.
Memory clue: 5 types: coarse, black, laterite, alluvial, yellow-brown.
Spot the difference
| Soil | Where | Feature |
|---|---|---|
| Coarse | Ajanta, Balaghat | Negligible humus |
| Regur | Deccan, Vidarbha | Black, low organic |
| Laterite | Konkan | Reddish-orange |
| Alluvial | Panvel-Uran | River mouths |
Practice questions
- 1Name the five soil types of Maharashtra.
- 2Where and how does coarse soil form?
- 3State features of regur soil.
- 4Why does laterite soil have a reddish colour?
- 5How does coastal alluvial soil form?
- 6Why is yellow-brown soil less useful for farming?
- 7What is GI status? Give examples.
- 8How do black and laterite soil arise from the same rock?
Show answers (try them yourself first)
- 1Coarse, regur, laterite, coastal alluvial, yellow-brown.
- 2On western plateau hills; weathering, low rain.
- 3Black; medium rain; low organic.
- 4Iron reacts with oxygen.
- 5Silt of short fast rivers settles at mouths.
- 6It is not very fertile.
- 7A recognition of a crop’s regional speciality; Haapus.
- 8Different climate: dry Deccan, humid Sahyadri.
Soil Erosion, Degradation and Conservation
In heavy rain the top soil of a field washes away and takes thousands of years to rebuild.
Loss of the top layer by wind or water is soil erosion. A fall in soil quality through excess chemicals or irrigation is soil degradation. Efforts to prevent them are soil conservation.
Key idea 1 : Erosion — Running water, climate and diversity of physiography cause erosion. When the top layer goes, humus and nutrients go too. Strong wind and water carry soil away unchecked.
Key idea 2 : Degradation — Excess chemical fertilisers, pesticides and weedicides for higher yield damage soil. Over-irrigation draws salts up, making soil saline and unproductive. Chemical residues stay for years, threaten microorganisms, reduce humus and deprive plants of micronutrients. A disturbed soil pH is a sign of degradation.
Key idea 3 : Conservation — The Soil Conservation Department builds embankments with trees on them and gully plugs on steep slopes. Trees slow the wind and roots hold the soil. Continuous contour trenches (CCT) dug along slopes slow water and let it seep in. Under Maharashtra’s watershed development the scheme “Arrest water, let it percolate” succeeded and raised groundwater levels; recently the Jalayukt Shivar scheme began.
- Easy : Erosion is? — Loss of the top layer.
- Medium : Effect of over-irrigation? — Soil turns saline.
- Exam-type : CCT means? — Continuous contour trenches.
In the figure: Ways to stop erosion.
As per the textbook the Government of Maharashtra ran “Arrest water, let it percolate” through watershed development and recently launched Jalayukt Shivar. (as per the textbook)
Erosion = goes; degradation = spoils; conservation = saves.
More fertiliser does not mean more fertility; overuse spoils soil.
Memory clue: Trees + trenches + bunds = soil saved.
Spot the difference
| Point | Erosion | Degradation |
|---|---|---|
| Meaning | Loss of top layer | Quality falls |
| Cause | Wind, water | Chemicals, over-irrigation |
Practice questions
- 1What is soil erosion?
- 2State the causes of erosion.
- 3What is soil degradation?
- 4Why does over-irrigation make soil saline?
- 5State the effects of excess chemicals.
- 6Write soil conservation measures.
- 7How does CCT save both soil and water?
- 8How do trees reduce erosion?
Show answers (try them yourself first)
- 1Loss of top layer by wind or water.
- 2Running water, climate, physiography.
- 3A fall in soil quality.
- 4Water pulls salts upward.
- 5Fewer microbes, less humus, disturbed pH.
- 6Bunds, trees, CCT, gully plugs.
- 7Slow water and let it seep in.
- 8Slow wind; roots hold soil.