The most appropriate irrigation methods widely in practice

The most commonly used methods were described in this presentation

1. What is the most
appropriate irrigation
method

2. Key issues
•capital v. recurrent costs
•salinisation risk
•uniformity
•minimisation of wastage and use of water
•minimising labour costs and increasing
automation if labour cost

3. Topography
Ifuniformslopesandnottoosteep,surfacemethodsOK
Iftopographyundulating-usesprinklerordripmethods
Surfacemethodscannotbeeasilyusedonfarmswithrocky
orsandysoil,steepslopes,badlybreakinghillsorgullies
Landgradingneededforgoodsurfaceirrigation
Landlevellingisexpensive-iftoomuchisrequireditmay
becheapertousesprinklersordripirrigation
Evenwithrelativelyflatlandsubsoilcanbecome
exposedandcropscanbeveryvariable

4. Soiltypes:
LowWCsrequirefrequentlightirrigations&sprinklersor
otheroverheadmethodsmightbebetter.
Highinfiltrationmayleadtohighlossesfrompercolationif
surfacemethodsusedsosprinklersordripbest.
Otherwise,shortfieldsrequired->increaseslabourcosts,
wastesland(headland/roads,mechanisationproblems(e.g
turning)
Ifsoilsveryvariable(heterogeneous),easiertoadapt
sprinklerordriptypes.

5. EffectonSoil:
•Surfaceirrigationtendstoencourageerosionandleachingof
nutrients.
•Insprinklerirrigation,thoughpoordesigncancause
compactionandsealing,properapplicationeliminates
erosion,compaction,sealing,andleaching

6. Water table:
Irrigation efficiency of surface irrigation always lower than
overhead.
If high water table (<4 m), drains will be required.
This is expensive.
In this case, better to use sprinklers or drip as there will be less
percolation.
Better control possible with overhead or drip systems usually,
underground drains will not be needed.

7. Water Losses
Surface irrigation loses water through porous ditches, deep
percolation, run-off. and evaporation Sprinklers and drip lose
water mainly through evaporation
Sprinklers requires 15 to 60% less water than surface methods
IrrigationEfficiency(waterusedbyplantas%ofapplied
water)is25-70%forsurfacemethods,60-80percentfor
sprinklersandevenhigherfordripirrigation

8. Wateravailability
Ifinshortsupply(orexpensive),usesprinklersordrip-or
makesurecanalslinedandmanagementisv.good
Landavailability
Sprinkerordripsystemshavelesslossoflandtoirrigation
structuressuchasditches,canals,etc

9. Waterquality
Sprinklers/dripcannotbeuseddirectlyifsedimentorsewage
inwater-thoughsedimentcanberemovedwithfiltration
equipment
Ifsoilissaline,leachingisoftencheaperusingsurface
irrigation.
ButifWTissaline-lesslikelytorisewithsprinklers/drip

10. Climate
Ifwind>15to20kph-donotusesprinklers(distortionof
distributionpattern)
Heavyraininirrigationseasonmayexacerbateproblemof
mechanisedcutlivation->sprinklersordrip
Crop
Tall(e.g.sugarcane)-difficulttomovepipes.
Ifsusceptibletomoisturestress-surfaceleastsuitable
(intervalsbetweenirrigationsusuallylonger)Canuse
sprinklerordripformostcropsexceptrice

11. CropGermination
Surfaceirrigationtendstobeslowerthansprinklerordrip
irrigation-light,evenapplicationsofwater.
Operatingconditions
Ifhistoryofsurfaceirrigation-maybemorelikelyto
succeedthansprinkers,e.g.Gezira,Sudan.
Sprinkersystemscanmakedowithlessexperiencedlabour
thanforsurfaceirrigation.
Schedulingeasieranddistributionmoreevenwithnon-
surfacemethods.
Whatarelocalresourcesformechanisedorpumpdependent
systems.

12. Operatingconditions
Ifhistoryofsurfaceirrigation-maybemorelikelyto
succeedthansprinkers,e.g.Gezira,Sudan
Sprinkersystemscanmakedowithlessexperiencedlabour
thanforsurfaceirrigation.
Schedulingeasieranddistributionmoreevenwithnon-
surfacemethods
Whatarelocalresourcesformechanisedorpumpdependent
systems

13. Financialaspects-verysitespecific
Surfacesystemshavelowyieldstostart(levelling)
Sprinklersystemsarecheaperonrougher,lightersoils
Landvalueincreasedforsurfaceandoverheadirrigation
Labour Requirements
Surface irrigation requires from one-half to one person per
acre where land lays well.
Sprinkler systems require about half that of surface methods.

18. Fieldcapacity
Theupperlimitofavailablewater;
Traditionallydefinedasthemoisturecontentofasoil48hours
aftersaturationandsubsequentlybeingallowedtodrain;
Ahighproportionofirrigationwateraddedabove
fieldcapacityis“wasted”;
FChasalsobeenconsideredtobe:
0.33bars[33kPa]inUSAor
0.1bars[10kPa]intheUK
FCalsosometimesconsideredasthemeansoilmoisturecontentin
winter(coldclimates)whenthepotentialevapotranspirationissmall
(andsodrainageismainfactorgoverningequilibriummoisturecontent.