soils lecture

7/29/2019 SOILS Lecture

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Soil Formation



Soils

– Loose material and uppermost layer of earth’s crust.

–Provides nutrients & water to plants.

Next to Water- man’s most viatal NaturalResource.

Most Significant result of Weathering

End product (formed due to) of Decay &

Disintegration of ROCKSContinuous & Time consuming Process

Soil is DYNAMIC system- detached from

environment – inert mass of Weathered rock



Soils

Factors affecting soil formation:Climate

Vegetation

Age of rock Relief andParent rock



Soil Components

Organic matter

Inorganic matter

Livingorganisms

Deadorganisms

Litter Detritus

HumusInorganicminerals

Organic Fraction

InorganicFraction



Different soil types develop

in different climates.



Soil Profile

During development – Soil- from Parent rock- Transformation proceeds certain well

defined stages- Series / Horizons

Although horizons differ in chemical and physical characteristics – Genetically

related



Soil Profile = layers in soil observedwith depth; Individual layers are

horizons

Bedrock

O horizon – contains litter onsurface, humus + OM beneath

A horizon – various stages of breakdown of organic matter

B horizon – mineral soil in whichorganic compounds have been

converted into inorganic

C horizon – unmodifiedparent material



Soil development

Formation of particular soil type from aCERTAIN PARENT material- Deccan Traps

Soil Erosion- Chain of transformationof soil type in to another due to changingenvironmental conditions

Grassland - forest



SOIL EROSION

– Removal of top soil by different agents.

CAUSES:

– Deforestation

– Overgrazing.

– Faulty method of Agriculture.

– Erosion by rivers.

– Removal of top soil (for bricks, pots, tilesetc)

– Shifting cultivation.



SOIL EROSION

EFFECTS: – Loss of cultivable land.

– Reduction in soil fertility.

– Causes silting & may change river course.

– Results in lots of run off.

– Reduces percolation of ground water.



SOIL CONSERVATION

– Protection of soil from Erosion andDeterioration.

Measures For Soil Conservation: – Contour farming.

– Mulching ( spreading of grass, leaves onground).

– Afforestation and Reforestation.

– Controlled grazing.

– Construction of dams and barrages – Crop rotation.

– Sub soiling.

– Terrace farming.



Genetic Classification

Residual soils – suffered no transport,infertile

Transported soils-places for off-heterogenous

Colluvial- moved under gravity- slopes

Alluvial- streams, flood, fine, stratified

Eolian- wind deposits



SOILS OF INDIA

Eight major types according to Indian Councilof Agricultural Research (ICAR). – Alluvial soils

– Black soils – Red soils

– Laterite soils

– Desert soils

– Mountain soils

– Saline and Alkaline soils

– Peaty and Marshy soils



ALLUVIAL SOIL

– Formed by deposition of alluvium by rivers.

– Occupies 15 Lakh sqkm area in India.

–Contribute greatly in agriculturaldevelopment.

Two types: KHADAR & BHANGAR

KHADAR : Newer alluvium. – Sandy, pale brown composition.

– Found in lower areas.

– Flooded every year.



ALLUVIAL SOIL

BANGAR : Older alluvium.

– Clayey & dark in colour.

– Coarse in nature. – Contains Kankar (lime nodules), Pebbles

and Gravels.

– Represents riverine alluvium of Himalayanrivers.



ALLUVIAL SOIL

Characteristics: Transported soils.

– Coarser in upper section and finest in delta.

– Light to dark in colour.

– Rich in Potash & Humus.

– Poor in Phosphorous and Nitrogen.

– Highly fertile, good for all crops (kharif & rabi).

– Crops: Rice, Wheat, Sugarcane, Cotton, Jute . – Areas: Punjab, Haryana, U.P, Bihar, W.B, Assam,

Parts of Orissa, delta regions of S.India



BLACK SOIL

– Also known as Regur or Black Cotton soil.

– Dark grey to Black in colour.

–High clay content.

– Highly moist retentive.

– Develops cracks in summer.

– Covers 5.4 lakh sqkm.

– Highly suitable for cotton. – Rich in iron, lime, calcium, Magnesium,

carbonates, and alumina.



BLACK SOIL

– Poor in Phosphorous, Nitrogen and Organicmatter.

– Areas: Deccan Trap which includes: Maharastra, W n

M.P, Parts of A.P, N n

Karnataka, Parts of T.N and Rajasthan.

– Crops: Cotton, Sugarcane, Groundnut,

Millets, Rice, Wheat, Oilseeds .



RED SOIL

Formed due to weathering of oldcrystalline rocks.

– More sandy and less clayey. – Rich in iron, small amount of Humus.

– Poor in phosphorus, nitrogen and lime.

–Slightly acidic and do not retain moisture.

– 3.5 lakhs sq.km area.

– Porous and Friable.



RED SOIL

Area :

– Tamil Nadu, Southern Karnataka, parts of Madhya Pradesh, Maharashtra, West Bengal, Eastern Rajasthan, North eastern States.

Crops :

– Ragi, Groundnut, millet, Tobacco, Potato,Rice, Wheat, Sugarcane.



LATERITE SOIL

Latin word meaning brick. – Formed under high temperature and

rainfall with wet and dry spell.

– Silica is leached due to high rainfall.

– Remnants of iron and aluminum oxides leftbehind is known as Laterite.

– Brown to Yellowish colour. – Becomes hard when exposed to

atmosphere.

– Used as building material.



LATERITE SOIL

– Rich in Iron.

– Poor in Lime, Potash, & Magnesium.

– Occupies 2.4 Lakh sqkm.

Areas: Parts of Assam, Karnataka, T.N, A.P, M.P, Kerala .

Crops: Tea, Coffee, Cashew, Rubber and Coconut.



DESERT SOIL

– Contains soluble salts.

– Originated by Mechanical disintegration & wind deposit.

– Porous and coarse.

– 90% sand & 5% clay.

– Rich in Nitrates & Phosphates.

– Poor in Nitrogen & Humus. – Friable, sandy & low moist content.

– 1.4 Lakh sqkm.



DESERT SOIL

Areas: Arid and Semi arid regions of Rajasthan, S

n Haryana, Punjab, N

n

Gujarat.

Crops: Drought resistant crops like millets and barley.



MOUNTAIN SOIL

– Found in hill slopes.

– Formed by deposition of organic matter

from forest. – Rich in humus.

– Poor in Potash and Lime.

Areas: Assam, Kashmir, Sikkim & Arunachal Pradesh.

Crops: Tea, Coffee, Spices & Tropical Fruits.



SALINE & ALKALINE SOIL

– Contains salts like Sodium, Magnesium,Calcium.

– Infertile, unfit for cultivation.

– Sandy to loamy in texture.

Areas:

– Parts of Gujarat, Rajasthan, Punjab,Haryana, U.P & Maharashtra.



PEATY AND MARSHY SOIL

– Occur in Humid region.

– Formed by accumulation of organic matter.

– Black in colour.

– Highly acidic and heavy.

Areas:

– Kottayam & Alleppey in Kerala, Coastal Orissa, Sundarbans of W.B



Dark Color IndicatesOrganic Matter



Soil Texture

Soil texture classified based on %composition as clay, silt, silty clay, loam(mix of all 3 sizes), clay loam, etc.

Organic matter = breakdown materialderived from living organisms = notincluded in soil texture

Clay –

type of clay is important fornutrient and water-holding capacity, abilityto form aggregates, etc.

P i i il h d k f



Prairie soils have a dark surfacelayer (horizon), are rich in minerals,and form in grasslands widespread

across Earth’s middle latitudes.

Soils-4-2

Images: NRCS

F t il h li ht



Forest soils have a light gray upperhorizon, a horizon rich in aluminumand/or iron, and form in warm to

cool humid regions where coniferousforests grow.



Tropical soils are reddish and iron-oxide rich, depleted in nutrients, and

form in humid and warm regions.



Organic soils are dark colored, rich indecomposed organic matter, and form

in poorly drained lowlands such asswamps and wetlands.



Desert soils form in arid settings andare commonly rich in calcium

carbonate.

Tundra soils form in Arctic



Tundra soils form in Arcticenvironments, have a dark organic-rich

upper layer, and a mineral rich layer

over frozen ground.

Soils-4-7Images: Travis Hudson, Alaska/Yukon Society of Professional Soil Scientists

soils lecture

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