Role of soil aeration for crop growth and its development.ppt

Soil Aeration reduces compaction, oxidizes the soil, and allows the roots to take the appropriate nutrients and grow as vigorously as possible.
With the help of better mechanization the soil is perforated with small holes to allow air, water and other nutrients to reach deeper.
There is no easy simple way to determine whether the soil aeration potential is good or poor.
Personal knowledge of the soil and the response of plants grown in it are the best sources of information for the grower.
Poor soil aeration improves the environment for plant diseases so that their attacks are much more severe than good soil aeration conditions, so providing better aeration is a good condition for plant development.

2. ACHARYA N G RANGA AGRICULTURAL
UNIVERSITY
S.V.AGRICULTURAL COLLEGE,TIRUPATI
COURSE NO : SOILS 501
COURSE TITLE : SOIL PHYSICS
TOPIC : Role of SOIL Aeration for crop growth
and its development
SUBMITTED TO:
Dr. G.P. Leelavathy
Assistant Professor
Department of Soil science and Agricultural
chemistry.
SUBMITTED BY:
N.RANGASWAMY
TAM/2020-24

3. Flow of presentation
Soil air definition & it's importance
Composition of soil and atm air
Factors affecting the composition of soil air
Process of gaseous exchange
Factors affecting mass flow
Diffusion
Characteristics of soil aeration
Factors affecting soil aeration
Influence of soil aeration on plant growth
Air permeability
ODR( oxygen diffusion rate)
Management of soil aeration
Plant Adaptations-
Root Respiration
Conclusion

4. What is Soil Air?
Thethreemajorcomponentsofsoilsaresolid,liquid(water),andgas
(air).
Soilsolidsaresoarrangedthatabout50%ofsoilvolumebecomesvoid
orporespace.
Thisvoidspaceisoccupiedbysoilwaterandsoilairbuttheirproportion
varies
So,soilairisthatpartofthesoilthatisnotoccupiedbysoilsolids
andsoilwater.
composition of soil air should have the following characteristics
Generallyoxygencontentdecreasesandthecarbondioxidecontent
increaseswiththedepthofthesoil.
Thehighercontentofcarbondioxideinsubsoilthanintopsoilissince
aerationofsurfacesoiltakesplacebetweentopsoilandatmosphere
whilethatofsubsoiltakesplacebetweensubsurfacesoilandsurface
soil

6. The carbon dioxide content of the soil shows a marked seasonal
variation, being higherin summer than in winter because of
greater root and microbial activity in summer.
The oxygen and carbon dioxide contents of soil air depend upon
the application oforganic matter, lime, and fertilizer in the soil
and vegetation on the soil.
Oxygencontent is lower and carbon dioxide content is higher in
manured, limed, fertilizedand vegetated soils than in
unmanured, unlimited, unfertilized and bare soils becauseof
greater root and microbial activity in manured and vegetated
soils.

7. The oxygen and carbon dioxide contents of the soil air depend
upon the porosity of the soil.
Oxygen content is lower and carbon dioxide content is higher
in fine-textured, poorly aggregated and/or compact soils than
in coarse-textured, well aggregated and/or loose soils because
of the difference in diffusion rate.
•Rainfall has a remarkable influence on the oxygen and carbon
dioxide contents of soil air.
•Oxygen content is lower and carbon dioxide content is higher
in wet soils than in dry soils because of restricted diffusion.
•Thus during the period of rain the soil becomes wet causing
reduction in oxygen content and an increase in carbon dioxide
content of soil air

8. Average composition of atmospheric and well-aerated soil air
[NOTE: The content of CO2, in soil air, vary from 10-10,000 times]

9. Factors Affecting the Composition of Soil Air
Soil texture
The amount of carbon dioxide increases and that of oxygen
decreases with an increase in the fineness of soil texture due to
variations of total porosity, macro pores, and water content of the
soil. For example, clayey soils usually contain more carbon dioxide
and less oxygen than loamy soils, and loamy soils contain more
carbon dioxide and less oxygen than sandy soils.
Soil structure
Soil structure also affects the composition of soil air, due to
variation of total porosity, macro pores and moisture content of the
soil.

10. The carbon dioxide content is higher and oxygen content is less
in poorly aggregated soil than in well-aggregated soil or a platy
type of structure than the spheroidal (granular and crumby) type
of structure.
For example granular soils Contain less than one-half as much
carbon dioxide as powdery soils.
Soil Compaction
As the compactness of a soil increases, the amount of total pore
space especially macro pores decreases causing a decrease in air
capacity and air permeability of the soil.
As a result the carbon dioxide concentration of soil air increases
and oxygen concentration of soil air decreases with an increase in
compactness of the soil.

11. Soil water content
Withtheincreaseinsoilwatercontent,aircapacitydecreasesdue
tothereductionofporevolumeforsoilair.
Airpermeabilityalsodecreaseswithanincreaseinsoilwater
contentduetotheblockageofporesthroughwhichrenewalof
soilairtakesplacesoil.
Carbondioxideproductionincreasesduetoanincreasein
biologicalactivityanddecompositionoforganicmatter.
Becauseofthese,thecarbondioxidecontentofsoilairincreases
andtheoxygencontentofsoilairdecreaseswithanincreasein
soilwatercontent.
Forexample,carbondioxidecontentofsoilairat30°Cincreases
about10timesassoilwatercontentchangesfrom6.8to26.8
percent

12. Organic matter content
Theamountofcarbondioxideinthesoilairisprimarily
dependentuponthedecompositionstageofsoilorganic
substancesandmodificationofthephysicalpropertiessuchas
soilstructure,porosityandsoilwatercontent.
Ifsoilorganicmattercontainsundecomposedorganicsubstances,
initiallythecarbondioxidecontentofsoilairincreasesduetothe
microbiologicaldecompositionoforganicmatterbutwhenthe
decompositionoforganicsubstancesisalmostcomplete,carbon
dioxidecontentdecreasesduetotheformationofgranularand
crumbystructureswhicharemoreporous,throughwhichmore
gaseousexchangetakesplace.

13. Soildepth
Subsoilsareusuallymoredeficientinoxygenthansurfacesoils
becauseoftotalporespaceaswellasmacroporespace.
Againaerationofsurfacesoiltakesplacebetweensurfacesoil
andatmospherewhilethatofsubsurfacesoiltakesplacebetween
surfacesoilandsubsurfacesoil.
Asaresulttheopportunityforgaseousexchangedecreaseswith
increasesinsoildepth.
so,carbondioxidecontentincreasesandoxygencontent
decreaseswithanincreaseinsoildepth.
Environmentalcondition
(RainfallandTemperature)Temperatureinfluencesthecontent
ofoxygenandcarbondioxideinthesoilair,becauseofhigh
temperature,carbondioxideproductionishigherinsummerthan
inwinter.

14. Forthesamereason,soilaircontainsahigherproportionof
carbondioxideundertropicalconditionsthanundertemperate
conditions.
Thisisbecausehighertemperatureencouragesbiologicalactivity
andincreasestherateoforganicmatterdecomposition.
Theconcentrationofcarbondioxidealsogenerallyincreases
afterrainprobablybecauseofincreasedbiologicalactivityand
decompositionoforganicmatter;reductionofporevolumefor
soilairanddecreaseofairpermeabilityduetoblockageofair
passage
Becauseofthese,forashortperiodcarbondioxidecontentis
higherandoxygencontentislessinmanuredfieldsoilthanan
unmanuredfieldsoil.Hencejustaftertheapplicationof
farmyardoranyotherorganicmanures,theoxygencontentof
soilairdecreasesandthecarbondioxidecontentofsoilair
increases

15. Seasonalvariation
Thecarbondioxideandoxygencontentofthesoilairvaries
considerablyfromoneseasontoanother.
Thesevariationsareprimarilyduetochangesintemperatureand
soilwatercontent.
Thecarbondioxidecontentofthesurfacesoillayersislowerin
coldermonthsandhigherinwarmermonthsbecauseofgreaterroot
andmicrobialactivitiesandahigherrateoforganicmatter
decompositioninthecarbondioxidecontentofsoilairishigherand
oxygencontentinwarmermonths,Becauseofitlowerinsummer
seasonthaninwinterseason.

16. Plantrootactivity
Rootsofgrowingplantsconsumeoxygenandreleasecarbon
dioxideduringrespirationandtendtoreducetheoxygencontent
andincreasecarbondioxidecontentorsoilair.
Becauseofthissoilairofcroppedlandgenerallycontainsmuch
more(maybeabout1.5to10timesmore)carbondioxidethansoil
airoffallowlandandthiseffectismostnoticeablewhencrops
growingactively
Manuringandmicrobialactivity
Productionofcarbondioxideisassociatedwithmicrobialactivity
whichinturndependsontheamountanddecompositionstageof
addedmanures.
Manuringincreasesmicrobialactivitycausingreductionofoxygen
andincreaseofcarbondioxidecontentofsoilairduetomicrobial
respirationandmicrobiologicaldecompositionoforganicmatter.

18. Tillage-The exchange of gases is faster in tilled soils. A
shallow tillage encourages CO
2, in the topsoil in comparison to
a deep tillage.
Puddling required for growing rice decreases the macro pores
and results in poor aeration for succeeding crops like wheat.
Deep tillage Shallow tillage

19. Khonke(1968)itreferstothe"aircapacityofthesoil.
Thevolumeofporespacefilledwithairwhenthesoilisundera
tensionof50millibar.
Thisvalueisalsocalled"non-capillaryporosity’’.
Itcorrespondstoaporesizeof0.06mmorlargerindiameter
Oxygenisrequiredfortherespirationofplantroots,microbes,and
thesoilfauna.
TheCO
2,helpsinincreasingtheavailabilityofnutrientstoplants.
TheN,servesasasubstratefortheproductionofplant-utilizable
(available)nitrogenbysymbioticandnon’symbioticbacteria.
Watervaporpreventsthedesiccationofsoilandhelpsinthe
movementofwaterwithinthesoil.
Importance of Soil Air

20. A constant supply of O
2, essential, and is concentration should be
at least 10 percent for normal growth of the plants. Lack of O
2, is
more injurious to plants than an excess of CO
2, within the
reasonable limits (20%).
An excess of O
2, is also undesirable because it oxidises the
organic matter rapidly and dries the soil quickly.

21. Sufficient Oxygen
Brown mushy roots Bunchy white roots
Oxygen deficiency

22. Process of Gaseous Exchange
The exchange of gases between soil and the atmosphere
(renewal of soil air) is a natural process
It involves two mechanisms namely,
Mass flow
Diffusion.
Themassflowofairoccursduetothetotalpressuregradientof
gaseswhichcausesthemovementofanentiremassofairfroma
regionofhigherpressuretoaregionoflowerpressure.
Massflowofairmayoccurfromatmospheretosoilandfrom
onelocationtoanotherinthesoil.
Thedifferenceintotalpressuremayariseduetometeorological
factorssuchastemperature,pressure,windandairreplacement
duetoirrigation.
Massflow

23. Massflow:Ionsmoveinthesoil
solutiontotheplantrootsasa
functionoftranspirationof
lossthewaterfromtheleaves
Ex:-Ca,Mgandanions
Diffusion:Nutrientionsmovefrom
hightolowconcentrations
(Concentrationgradient)
Ex:-K&P

24. Diffusionisthemoleculartransferofgases.
Themoleculesofgasesareinastateofmovementinall
directions.
Throughthisprocesseachgastendstomoveinadirection
determinedbyitspartialpressure.
Diffusionallowsextensivemovementfromoneareatoanother
evenifthereisnooverallpressuregradient.
Diffusionisthepredominantprocessofsoilaeration.
Indiffusion,individualgasconstituentsmoveseparatelydueto
partialpressuregradientbutthetotalpressureofairmaybethe
same.
WhenthepartialpressureofCO
2,insoilairincreasesduetoroot
andmicrobialactivities,theCO
2,diffusesfromthesoiltothe
atmosphere.
Diffusion

26. Factors affecting the mass flow
Temperature-AsperCharles'lawairpressureisdirectly
proportionaltotheairtemperatureataconstantvolume.
So,wheneverthereisatemperaturegradientbetweentwopoints,a
pressuregradientdevelopswhichcausesgasestomove
Pressure-AsperBoyle'slaw,thevolumeofairisinversely
proportionaltothepressureataconstanttemperature.
Withtheincreaseinpressureintheatmosphere,thevolumeof
soilairdecreasesresultinginthemovementofairfromthe
atmospheretosoil.
Asthepressureintheatmospheredecreases,thevolumeofsoilair
increaseswhichcausesthemovementofsoilairtotheatmosphere

27. Rainfallorirrigation
Rainfallandirrigationdisplacethe
soilairassuchtothelowerdepths.
Whenwaterislostfromthesoilby
evaporation,plantuptake,ordeep
drainagetheairmovesfromthe
atmospheretothesoil.
Wind
Pressureandsuctioneffectsofhigh
windcausetheexchangeofgases
betweenthesoilandtheatmosphere
buttheeffectisrestrictedtosurface
soilonly

28. Similarly,whenO
2,insoilairisconsumedforrespiration,itspartial
pressureisreducedandtheO
2,diffusesintothesoil.
Diffusionincreaseswithanincreaseintemperature.
Soilaerationstatusmaybecharacterizedbydeterminingthe
concentrationofO
2,andCO
2,insoilairusingchemicalor
gaschromatographicmethods.
Theair-filledporosityandairpermeabilitycanalsobeused
todeterminetheaerationstatusofsoil.
Othermethodsincludethedeterminationofthediffusion
coefficientofgasesandtheredoxpotentialofthesoil.
However,thebestmethodforcharacterizationofaeration
statusistomeasuretheoxygendiffusionrate(ODR)inthe
soil.
Characterization of Soil Aeration Status

29. FactorsAffectingSoilAeration
Soilwatercontent:
Immediatelyafterheavyrainorirrigationbothmacroandmicro
poresarealmostfilledwithwaterandremovalofexcesswater
fromthesoilthroughdrainageand/orevaporationdetermines
theaerationstatusofthesoil.
Aircanenterthesoilporesonlywhensomeofthewateris
removed.
Diffusionofanygasthroughwater-filledporesismuchless
thanthroughair-filledpores.
Therefore,soilaerationdecreaseswithanincreaseinsoilwater
contentduetoareductioninporevolumeforsoilairand
blockageofporesthroughwhichrenewalofsoilairtakesplace.

30. Macroporosityofthesoil
Thevolumeofmacroporesofsoilisthemostimportantfactor
influencingsoilaeration.
Macroporesaffectthetotalairspaceandgaseousexchange
betweensoilairandatmosphericair.
Soiltexture,soilstructureespeciallyaggregatestability,andsoil
compactioni.e.bulkdensitydeterminethemacroporespaceand
inturnsoilaeration.
Soilaerationi.e.gaseousexchangebetweensoilairand
atmosphericairismoreincoarse-texturedsoilthanfine-textured
soil,inspheroidal(granularandcrumby)typestructurethan
platystructure,inwell-aggregatedsoilthanpoorlyaggregated
soil,inlesscompactedsoilthanhighlycompactedsoilandin
soilshavinghighhumuscontentthaninsoilshavinglowhumus
contentbecauseofincreaseinaerationporosity

31. Soilheterogeneity
Anyimpedingsoillayersuchasaheavytexturedorcompacted
soillayerorthepresenceofanypaninasoilprofilelimitsready
airexchangebetweensoilairandatmosphericairwhichinturn
decreasessoilaeration.
Tillage
Tillagegenerallyincreasesair-filledporositycausinganincrease
insoilaerationi.e.therateofgasdiffusioninthetopsoilfora
shortperiodafterploughing.Deepploughingandmouldboard
ploughingtonormaldepthgenerallyyieldthehighestratesof
gasdiffusion.
Tillagewithheavyimplementsalsomayformacompactlayer
belowtheploughingdepth.

32. Drainage
Drainageofwaterloggedlandsoruplandshavinghighwatertable
improvesoilaeration.
Improvementofdrainageconditionsinthesoilincreasesthesoil’s
oxygenstatusandreducesdenitrificationlosses.
So,airpermeabilityisgreateringeneralinploughedtopsoilfora
shortperiodthanintheunploughedtopsoilbutsimilarorless
afteralongperiodofploughingintheploughedtopsoilthanin
unploughedtopsoilandinsoillayerbelowtheploughingdepthin
theploughedfieldthanintheunploughedfield,

33. Influence of Aeration on Plant Growth
Different types of plants prefer to grow in different levels of soil
aeration.
Hydrophytes grow well with continuous flooding but
mesophytes and xerophytes normally grow better in well-aerated
conditions.
The effect of aeration on the growth of upland higher plants can be
divided into two categories:
The effect on the soil constituents which in turn influences growth
The direct effect on the physiological condition of plants.

34. The effect of aeration on the soil constituents
Oxygen content of soil air determines the nature as well as the rate
of microbial activity in the soil.
When oxygen is present in adequate amounts aerobic organisms
become active and oxidation reactions take place, If sugar is
considered as an example of an organic compound, the following
oxidation reaction occurs :
(Sugar) C
6H
12O
6+ 60
2-------6CO
2+ 6H
2O
The presence of adequate oxygen in the soil is conducive to the
production of highly oxidized soil constituents, which usually
provide a physical and chemical environment suitable for good
plant growth.
The oxidized states of nitrogen and sulfur are readily utilized by
higher plants.

35. Thecarbondioxideproducedbybiologicalactivityandwaterform
carbonicacidwhichincreasesthesolubilityofmanysoilminerals
forwhichplantnutritionandfertilitystatusofsoilisincreased.
Carbondioxidedissolvedwaterusuallyincreasesthesolubilityof
naturalphosphatemineralsinsoil.
themineralsareconvertedtovariousformsofcalciumphosphate
bytheactionofcarbondioxide.
Intheabsenceofadequateoxygeninthesoil,anaerobic
organismsbecomeactive,andorganicmatterisreducedto
alcohols,aldehydes,ormethane.
Thereducedreactionsoccuratamuchslowerrateoneexampleof
whichisstatedbelow:
C
6H
120
6------3CO
2+ 3CH
4

36. Sounderanaerobicconditions,biologicalreactionsthattake
placeinsoilreducetheoxygenofmanysoilconstituents,
therebycreatingchemicalconditionsthatarenotfavorableto
thegrowthofmosthigherplants.
AirPermeability
Airpermeabilityofsoilisaparameterthatindicatesits
readinesstotransmitgaseswhenadifferenceinpressurebuilds
up.
Thepercentage,size,andcontinuityofporeswithinthesoiland
occupiedbytheairdeterminethepermeabilityofthesoil.
SpecialinstrumentslikeanairPermeameter"andagasometer"
areusedtodeterminetheairpermeability.

37. ODR(OxygenDiffusionRate)
TherateatwhichO2,isreplenishedwhenitisusedbyplant
rootsormicroorganisms.
TheODRmeterisusedtomeasureODR(Platinum
microelectrodetechnique).
ThecriticalvalueofODRofsoilsis20x10-8g/cm
2
/minbelow
whichthegrowthofrootsofmostplantsceases.

38. Schemeofsoiloxygendynamics.Jisgasdensityflux,cisgasconcentration(gm-
3),tistime,xisdistance,Smismicroorganismrespiration,Spisplant
respiration,andSrisredoxreactionsinthesoil.

39. The optimum ODR range for most crops lies between 30x10
-8
to
40x10-8g/cm²/min.
The ODR decreases with moisture and depth of soil.
A soil condition where the ODR is at least 30x10
-8
g/cm²/min and
O
2, the concentration of the soil air is at least 10% in the root zone
is considered as having “adequate aeration"

40. ManagementofSoilAeration
Thesoilaerationcanbeoptimizedbymanagingsoilstructure,soil
temperature,properdrainage,tillage,plantadaptationand
regulationofplantroots.
SoilStructure
Soilstructuremaybeimprovedbytheadditionoffarmyard
manure,greenmanuring,cropresidues,andthegrowingof
legumecropstoincreasethevolumeofmacropores.
Ifmoremacroporesarepresentinthesoilwhichcondition
facilitatesgoodaerationinthesoil.
Drainage
Thedrainagewilldecreasethemoisturecontentandprovidean
aerobicenvironmentinthesoil.

41. Cultivation
Ashallowcultivationofthesoilandinter-cultureoperations
controlweedsandhelpintheexchangeofgases,especiallyin
poorlydrainedheavy-texturedsoils
Afterrain,ifcrustformsitmayhinderthegaseousexchange,a
lightcultivationwillbreakitandhelpinimprovingsoil
aeration.
Temperature
Anincreaseinsoiltemperatureincreasestheoxygendiffusion
rates,enhancesmicrobialactivity,andraisesCO
2,productionin
thesoil.
Thenetresultoftheincreaseinsoiltemperatureonthepartial
pressureofO
2,may,therefore,beeitherpositiveornegative.

42. Insuchsituationsmulchingplaysanimportantroleasmulch
protectsthesoilfromtheimpactofraindropsandtherefore,
helpsinretainingthetilth.
Thusmulchingfacilitatesaerationbutitalsokeepsthesoil
moistandrestrictsthesoilaeration.
Thepositiveornegativeeffectofmulchingonoxygen
diffusionratedependsonthesoil’ssituation.
However,ithasbeenobservedthatmulchingusuallydecreases
theO2,diffusionintothesoil.
PlantAdaptations
Plantroots,ingeneral,areadaptedtoaerobicconditions.
However,someoftheplantspeciesdevelopmechanismssuch
asanincreaseintheairspaceofroots(moreporosity)or
internalaerationthroughleavesandcortexcellsandgrowwell
eveninoxygen-deficientsoil.

43. Submerged Roots

44. [NOTE: Rice thrives well in submerged conditions and soybean
crops can tolerate temporarily waterlogged conditions better
than crops like maize, pigeon pea and other deep-rooted Tops)
Regulation of Root Respiration
Soil aeration may be managed by regulating the respiration of
roots and microbes by fertilization, cultural practices, plant
population, and incorporation of organic residues into the soil.
Crops of lower O
2, requirement or shallow-root systems may
be grown in situations where only surface soil has some degree
of aeration.

46. SoilAerationreducescompaction,oxidizesthesoil,andallows
therootstotaketheappropriatenutrientsandgrowas
vigorouslyaspossible.
Withthehelpofbettermechanizationthesoilisperforatedwith
smallholestoallowair,waterandothernutrientstoreach
deeper.
Thereisnoeasysimplewaytodeterminewhetherthesoil
aerationpotentialisgoodorpoor.
Personalknowledgeofthesoilandtheresponseofplants
growninitarethebestsourcesofinformationforthegrower.
Poorsoilaerationimprovestheenvironmentforplantdiseases
sothattheirattacksaremuchmoreseverethangoodsoil
aerationconditions,soprovidingbetteraerationisagood
conditionforplantdevelopment.
CONCLUSION