crop water requirement and different methods.ppt

crop water requirement

1. CROP WATER REQUIREMENT-FACTORS AFFECTING CROP WATER
REQUIREMENT
Cropwaterrequirementisthewaterrequiredbytheplantsforits
survival,growth,developmentandtoproduceeconomicparts.
Thisrequirementisappliedeithernaturallybyprecipitationor
artificiallybyirrigation.
Hence the crop water requirement includes all losses like:
a)Transpirationlossthroughleaves(T)
b)Evaporationlossthroughsoilsurfaceincroppedarea(E)
c)Amountofweatherusedbyplants(WP)foritsmetabolsmThese
threecomponentscannotbeseparatedsoeasily.
HencetheETlossistakenascropwateruseorcropwater
consumptiveuse.

2. d)Otherapplicationlossesareconveyanceloss,percolationloss,
runoffloss,etc.,(WL).
e) The water required for special purposes (WSP) like puddling
operation, ploughing operation, land preparation, leaching,
requirement, for the purpose of weeding, for dissolving fertilizer and
chemical, etc.
Hencethewaterrequirementissymbolicallyrepresentedas:
WR = T + E + WP + WL + WSP
or
WR = IR + ER + S
or
WR = CU + WL + WSP
CU = E + T + WP
IR-Irrigationrequirement;ER-Effectiverainfall
S-Contributionfromgroundwatertable.

3. Thecropwaterrequirementvariesfromplacetoplace,fromcropto
cropanddependsonagro-ecologicalvariationandcropcharacters.
Thefollowingfeatureswhichmainlyinfluencethecropwater
requirementare:
1) Crop factors
a) Variety
b) Growth stages
c) Duration
d) Plant population
e) Crop growing season
2) Soil factors
a) Structure
b) Texture
c) Depth
d) Topography
e) Soil chemical composition

4. 3)Climaticfactors
a)Temperature
b)Sunshinehours
c)Relativehumidity
d)Windvelocity
e)Rainfall
4)Agronomicmanagementfactors
a)Irrigationmethodsused
b)Frequencyofirrigationanditsefficiency
c)Tillageandotherculturaloperationslikeweeding,mulchingetc

5. Irrigationrequirement
Thefieldirrigationrequirementofcropsreferstowaterrequirement
ofcropsexclusiveofeffectiverainfallandcontributionfromsoilprofile
Itmaybegivenasfollows
IR -WR –(ER + S)
IR-Irrigationrequirement;WR-Waterrequirement;ER-Effective
rainfall;S-Soilmoisturecontribution
Irrigationrequirementdependsuponthe
a)Irrigationneedofindividualcropbasedonareaofcrop
b)Lossesinthefarmwaterdistributionsystemetc.
Allthequantitiesareusuallyexpressedintermsofwaterdepthper
unitoflandarea(ha/cm)orunitofdepth(cm).

6. Netirrigationrequirement
Itistheactualquantityofwaterrequiredintermsofdepthtobring
thesoiltofieldcapacityleveltomeettheETdemandofthecrop.
d=Netirrigationwatertobeapplied(cm)
Mfci=FCinithlayer(%)
Mbi=Moisturecontentbeforeirrigationinithlayer(%)
Ai=Bulkdensity(g/cc)
Di=depth(cm)
n=numberofsoillayer

7. Grossirrigationrequirement
Thetotalquantityofwaterusedforirrigationistermedgross
irrigation
requirement.
Itincludesnetirrigationrequirementandlossesinwaterapplication
andotherlosses.
Thegrossirrigationrequirementcanbedeterminedforafield,fora
farm,foranoutletcommandarea,andforanirrigationproject,
dependingontheneedbyconsideringtheapproximatelossesat
variousstagesofcrop.
Net irrigation requirement
Gross irrigation = --------------------------------x 100
Field efficiency of system

8. Irrigationfrequency
Irrigationfrequencyistheintervalbetweentwoconsecutive
irrigationsduringcropperiods.
Itdependsupontherateofuptakeofwaterbyplantsandsoil
moisturesupplycapacitytoplantandsoilmoistureavailableinthe
rootzone.
Henceitisafunctionofcrop,soilandclimate.
Normally,irrigationshouldbegivenatabout50percentandnot
over60percentdepletion.
FC–moisturecontentoftherootzonepriortostartingirrigation
= ------------------------------------------------------------------------------
Peak period consumptive use rate of crop

9. Irrigationperiod
Irrigationperiodisthenumberofdaysthatcanbeallowedfor
applyingoneirrigationtoagivendesignareaduringpeakconsumptive
useperiodofthecrop
Netamountofmoistureinsoilatstartofirrigation(FC-PWP)
=----------------------------------------------------------------------------------
Peakperiodconsumptiveuseofthecrop
Criticalstagesforirrigation:
Thestageatwhichthewaterstresscausessevereyieldreduction
Itisalsoknownasmoisturesensitiveperiod.
Moisturestressduringthesensitiveperiodreducetheyield.
Formostofthecropstheleastsensitivestagesareripeningexcept
forvegetableslikeLettuce,Cabbageetc