Field Capacity of Water.ppt

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1. Field Capacity of Water

2. FIELD CAPACITY OF WATER
•Fieldcapacity(FC)istheamount
ofsoilmoistureorwatercontent
heldinsoilafterexcesswaterhas
drainedawayandtherateof
downward movement has
decreased,whichtakesplace
within2-3daysafterarainor
irrigationinprevioussoil.
•Thephysicaldefinitionof(FC)is
thebulkwatercontentpresentin
soilat−33J/kgofthesuction
pressure
•FC=(θFC/100)×RD
Levels of moisture in soil

3. TYPES OF WATER IN SOIL
•TheSoilwaterisdynamic;removalofwateroccursdue
todrainage,evaporation,andtranspirationandadditionof
wateroccurswithdewdrops,rainfall,andirrigation.
•Therearethreetypesofwaterinsoil.
1.GRAVITATIONAL WATER
2.CAPILLARYWATER
3.HYGROSCOPIC WATER

4. 1-GRAVITATIONAL WATER
•Amountofwaterthatis
drainedoffduetopullof
gravitytojoingroundwater
table.Largersoilparticles
thatdon’tretainwaterinit
andperculatesdowndueto
gravity.
•Thiswaterisnotavailable
totheplantsforgrowth

5. 2-CAPILLARY WATER
•Amountofwaterthatisretainedagainstthepullofgravitydueto
surfacetension.
•Capillarywateristhatwaterthatisheldinmicrosporesofthe
soil,andcomposesthesoilsolutionbecausesurfacetension
properties(cohesionadhesionforces)ofsoilismuchgreaterthan
thatofforceofgravity.
•Asthesoildriesout,poresizeincreasesandthecapillarywater
perculatesdowntogravitationalwater,inthiswaycapillary
waterchangestogravitationalwater.
•Capillarywateristhemainwaterthatisavailabletotheplantsas
itistrappedinsoilsolutionrightnexttotherootsoftheplants.

6. 3-HYGROSCOPIC WATER
•Amountofwaterthatisadsorbedonthesurfaceofthesoil
particlesasaverythinfilmandstronglysticktothesoil
grain.Itisgenerallynotavailabletotheplantsbecausewater
issotightlyboundtothesoilparticlesbyadhesionproperties
andverylittleamountofwateristakenupbytheplants.
•Hygroscopicwaterisfoundonthesoilparticlesnotwithin
thepores.
•Example:Clay
•Hygroscopicwaterishelpfulforthegrowthoftheplants.

7. HOW WATER IS RETAINED IN SOIL
•Water retention capacity of soil is due to
their colloidal properties and aggregation
qualities.
•The water is held on the surface of the
colloids and other particles and in the
pores. The forces responsible for retention
of water in the soil after the drainage has
stopped are due to surface tension and
surface attraction and are called surface
moisture tension.
•This refers to the energy concept in
moisture retention relationships.
•The force with which water is held is also
termed as suction.
•That’s why we say that smaller soil
particles retain more water as compared to
that of larger soil particles.
Water retention capacity of soil.

8. SOIL MOISTURE RELATIONSHIP ( SATURATION CAPACITY )
•Amountofwaterpresentinsoil
whenallthesoilparticlesare
filledwithwater.
•Largersoilparticlesdon'tretain
waterandwaterperculatesdown
duetopullofgravityandjoin
gravitationalwater.Waterretain
afterthisisfieldcapacity
•SaturationCapacity=Ww/Ws
•Where
a)Wwistheweightofwater
b)Wsistheweightofsoil Soil water relation.

9. FIELD CAPACITY
•Weightofwaterretendinthesoilafter
gravitationalwaterhasdrainedoffthatis
thewaterexactlyrequiredbytheplants
fortheirgrowth.

10. PERMANENT WILTING POINT
•Criticalvaluebelowwhichrootcannotextractenoughmoisturedue
toincreaseinsoilmoisturesurfacetension.Atthispointwatercan’t
perculatesoutofsoilbecauseitisstrictlyadheretothesoil
particles.
•Itisthepointwhenthereisnowateravailabletotheplants.
Permanentwiltingpointdependsontheplantvariety,butitis
usuallyaround1500kPa(15bars).Atthisstage,thesoil
stillcontainssomewater,butitisdifficultfortherootstoextract
fromthesoilparticles.
•Ifwaterislessthanpermanentwiltingpointplantswiltandgrowth
isstoppedandplantsdie.

11. AVAILABLE WATER
•Theamountofwateractuallyavailable
totheplantsfortheirgrowth.
•Itisdeterminedasfieldcapacityminus
thewaterthatwillremaininthesoilat
permanentwiltingpoint.
•Theavailablewatercontentdepends
greatlyonthesoiltextureandstructure.
•θAWC=θFC-θPWP
•Where
a)θAWCismaximumavailablemoisture
content(%v/v)
b)θFCisthemoisturecontentatfield
capacitypoint(%v/v)
c)θPWP isthemoisturecontentat
permanentwiltingpoint(%v/v)
Different Level of water in Soil

12. READILY AVAILABLE WATER
•Amountofwaterthatiseasilyavailabletotheplants.
•Readilyavailable=75%oftheavailablewater
•(Total water) Vv = Vwy/V + Vwr/V
•Where:
a)Vwyisthevolumeofthewateryieldthatislostinformofgravitationalwater
b)Vwristhevolumeofthewaterretendinthesoilparticlesandavailabletotheplants
c)Visthetotalvolumeofthesoil
d)Vv=Sy+Sr
e)WhereSyisspecificyield,Srisspecificretention
SPECIFIC YIELD (Sy)
•Ratioofthevolumeofthewateryieldtothetotalvolumeofthesoil.
SPECIFIC RETENTION (Sr)
•Ratioofthevolumeofwaterretainedagainstgravitytothetotalvolumethesoil.

13. FACTORS THAT INFLUENCE THE FIELD
CAPACITY OF WATER
•The various factors that influence the water holding capacity
1)PREVIOUSSOILWATERHISTORY
2)SOILSTRUCTURE
3)SOILTEXTURE
4)TYPEOFCLAY
5)ORGANICMATTER
6)TEMPERATURE
7)DEPTHOFWETTING
8)EVAPOTRANSPIRATION
9)SOILMOISTURECONTENT

14. PREVIOUS SOIL WATER HISTORY, SOIL
STRUCTURE , And SOIL TEXTURE
•Awettingsoilandadryingsoilholddifferentamountsof
water.Asoilthatissaturatedandthendrieshasahigherfield
capacitythanasoilthatisbeingwetted.
•Soilstructurehasdirectrelationtotheamountofwaterit
contain.
•Thesmallerthesoilparticles,greaterwillbewaterretention
capacityofsoil.Clayhasmorewaterholdingcapacitythan
sand.Smallersoilparticles(clay)havemoreporesorcapillary
spacessotheyhavehighwaterholdingcapacity.Largersoil
particles(sand)havefewcapillaryspacessotheyhaveless
waterholdingcapacity

15. TYPE OF CLAY and ORGANIC MATTER
•Thehigherthecontentofmontmorillonite,greateristhe
amountofwaterretainedinit.Montmorilloniteisatype
ofclay,averysoftgroupofmineralsthatformwhen
theyprecipitatefromwatersolutionasmicroscopic
crystals.
•Soilorganicmatterhelpsinretainingwater.Organic
matteraidsincementingparticlesofclay,silt,sandthat
aggregatesintosubstancewhichincreasesthewater
holdingcapacity.Decompositionoforganicmatteradd
essentialnutrientsinthesoilwhicharehelpfulforthe
growthofpants.

16. TEMPERATURE and EVAPOTRANSPIRATION
•Temperatureinfluencestheamountofwaterheld,
particularlyifthesoilhasbeenpreviouslywetted.The
amountofwaterretainedatfieldcapacitydecreasesasthe
soiltemperatureincreases.Thisresultsinincreasedrunoff
fromawatershedassoilwarmsandwaterretention
capacityofthesoildecreases.
•Combinationofwaterthatislostfromthesoilthrough
evaporationandtranspirationthroughplantsasapartof
theirmetabolicprocess.Therateandpatternofextraction
ofwaterbyplantrootsfromsoilcanaffectthegradients
andflowdirectionsintheprofile

17. DEPTH OF WETTING
•Wettertheprofileisat
theoutsetgreateristhe
depthofwettingand
greateristheextraction
ofwaterbyplantsroots
fromthesoilcanaffect
theflowofgradients.
Andatfieldcapacity,
thesoiliswetand
containallthewaterit
canhold.

18. SOIL MOISTURE CONTENT
•Soilmoisturecontent
indicatestheamountofsoil
presentinwaterpresentin
soil.Itiscommonly
expressedasamountofsoil
presentindepthof1mofa
soil.
•Example:whenamountof
water(inmmofwaterdepth)
of150mminadepthofof1m
ofasoil,soilmoisturecontent
is150mm/m.

19. IMPORTANCE OF FIELD CAPACITY
•Soilwaterservesasasolventandwaterisuptofieldcapacityit
actascarrieroffoodnutrientsforplantgrowth.
•Theyieldofacropismoreoftendeterminedbytheamountof
wateravailableratherthanthedeficiencyofotherfoodnutrients.
•Soilwaterregulatessoiltemperature.
•Microorganismsrequirewaterfortheirmetabolicactivities.
•Fieldcapacityofwaterhelpsinchemicalandbiological
activitiesofsoil.
•Waterisessentialforphotosynthesisandplantscansynthesize
theorganicmatterifwaterissuppliedtotheplantsuptofield
capacity.

20. ESSENTIAL CONDITIONS TO DETERMINE THE
FIELD CAPACITY
•Saturatethesoilprofiletothedepthunderstudyby
addingexcessofirrigationwater.
•Minimizetheevaporationlossesfromthesurface.
•Eliminatethetranspirationlossesbyworkingonnon-
croppedfields.
•Selecttheplotscontaininguniformandfreedraining
soil.
•Observethetimerateofdecreaseinmoisturecontent.

21. METHODS OF MEASURING FIELD
CAPACITY
Therearevariousmethodsofmeasuringfield
capacityofwaterbuttwomethodsaremainly
described.
1)Pressurebasedmethod.
2)Fluxbasedmethod.

22. 1.PRESSURE-BASED METHOD
•Pressurebasedmethod
wasintroducedby
RichardandWeaverto
estimatethefieldcapacity
todeterminewithasoil
watercontentatamatrics
potentialof-33kPa.
•ForPressurebased
method,Fieldcapacityis
determinedbyretention
curvemethod.
Water retention curves for sand clay
and loam

23. 2. FLUX –BASED METHOD
•FromtheFluxbasedmethod,thefieldcapacity
canbeestimatedfromtheunsaturatedsoil
hydraulicconductivityfunctionwitha
predefinednegligiblefreedrainageflux.
•Withtheunsaturatedsoilhydraulic
conductivityunderthefieldcapacity
conditions.

24. Thank You