Water quality in drip irrigation附翻译.docx
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Waterqualityindripirrigation附翻译
附录英文翻译
Waterqualityindrip/trickleirrigation:
Areview
ES.Nakayama1andD.A.Bucks2
1USWaterConservationLaboratory,4331EastBroadway,Phoenix,AZ85040,USA
2USDepartmentofAgriculture,AgriculturalResearchService,NationalProgramStaff,Beltsville,MD20705,USA
Summary.:
Theintensivetreatmentofirrigationwaterre-quiredfortheproperoperationofdripirrigationsystemsispresentlyanacceptedpractice.Tocontrolemitterclog-ging,weneedtoknowthebasiccausesofclogging.Themajorcloggingfactorshavebeenidentifiedandcontrolmeasuresdevelopedtopreventemittermalfunction.Allemittercloggingproblems,however,havenotbeensolvedprimarilybecauseofcost.Themainapproachtocontrolcloggingisproperwatertreatment.Thetypeoftreatmentisbasedonthequalityoftheirrigationwater,whichcanbeclassifiedintermsofitsphysical,chemicalandbiologicalcomposition.Thecausesofemittercloggingandpossiblewatertreatmentandpreventivemeasurestomaintainreliableoperationarereviewed。
Waterqualityandemitterclogging
Dripirrigationinthemid-1960'sthroughmid-1970'swasconsideredanemergingtechnologywithitsapplicationlimitedonlytohigh-priced,specialtycrops.Todayitisusedonawidevarietyofcrops,eventhosethatwereinitiallyconsideredunprofitableformanagementunderdripirrigation.
Throughcarefulnurturing,dripirrigationhasgrownintoastableandeconomicallysignificantpartofthefarmingcommunitywhichhasalsohadgreatimpactontheirrigationandassociatedindustries.Initsinfancysomedifficultandseeminglyunsolvableproblemswereencounteredinoperatingdrip/tricklesystemsparticularlythoserelatedtothecloggingofemitters.Alsoduringthisperiod,numerousinventorsandentrepreneurssoldvarioustypesof"non-clogging"or"self-cleaning"emitterswhichwerepromisedtosolvethemostseriousproblemofemitterplugging,butunfortunatelydidnotadequatelydoso.Thecloggingproblem,ifnotproperlysolved,wouldhaveresultedinthecompleterejectionorsevererestrictionofapromising,efficientmethodofirrigationandwaterconservation.Workonimprovingdripsystemoperationswentalongtwodifferentdirections,independent,butcloselyintouchwithoneanother.Onegroupconcentratedonimprovingthehydraulicoperationoftheemitters;theotherfocusedonstudyingthecloggingprocessandfromsuchknowledgedevelopingproceduresforalleviatingthecloggingproblem.Themainconclusiondrawnfromthelattertypeofstudiesisthatcloggingiscloselyrelatedtothequalityofwaterusedinthedripsystem,e.g.Bucksetal.(1977),FordandTucker(1975),Gilbertetal.(1981),McElhoeandHilton(1974),Nakayamaetal.(1977),Pellegetal.(1974).Researchcontinuestobereportedonirrigationwaterquality,treatment,anduniformityofapplication(Hilletal.1989;KinoshitaandBui1988;Pad-makumariandSivanappan1985).Waterdivertedfromothertraditionalirrigationusageispresentlythemajorsourcefordripirrigation,butthissituationisbeginningtochangetowarduseofwastewaterfromcitiesandindustries.Thesetypesofwaterhavedifferentwaterquality,andconsequently,differentcloggingparametersareinvolvedsothatdifferentwatertreatmentproceduresmustbeused(Adin1987;AdinandElimelech1989;Chandra-kanthetal.1988;Gamble1986).
Causesofemitterclogging
Forsurface-placeddripsystems,inspectionoftheflowbehaviorcanreadilydeterminewhenanemitterisoperatingproperly.However,externalexaminationalonecannotgiveanaccurateevaluationofthecauseorcausesofemitterclogging.Mostcloggingstartsinsidetheemitteranditmaystartveryslowlyandprogressslowlyoroccuralmostovernight.Partialcloggingisjustasbadasacompletecloggingbecausetheybothreduceapplicationuniformityandalterthehydraulicsoftheentiresystem.Todeterminetheexactnatureofthecloggingprocess,carefulphysical,chemical,andbiologicalexaminationoftheemittersandsupplylinesmustbemade.Inaddition,Thecompositionofthewaterusedinthesystemmustbedetermined.Becauseofthevarietyoffactorsinvolved,amultidisiplinaryapproachmustbetaken.Tofocusfurtheronthemultiplecausesofemitterclogging,atablewasdeveloped,whichincorporatesalltheinformationavailableatthattimeonthefactorscontributingtoclogging(Table1).
Table1.Physical,chemicalandbiologicalfactorsinvolvedinemitterclogging(Bucksetal.1979)
Theresiduesforalargenumberofemittersandtubingwereexaminedchemicallyandmicroscopicallytoascertainthecomponentsofthecloggingmaterial.Informationonthecompositionsforvariouswatersourcesandtherelatedcloggingproblemsattherespectivesiteswereevaluated.Thecausesofcloggingvariedfromlocationtolocationsothateachsitewouldrequireadifferenttypeofwatertreatmenttopreventemitterclogging.Carbonatetypematerialswereprominentinsamplesfromthesouth-westernUnitedStates,whereasthemicrobialironclog-gingsubstanceswereabundantinthesamplestakeninthesoutheasternregion.Theprecedingfactors,however,arenotisolatedtoaspecificregion;instead,theyhavebeenobservedwithinthesameareaand,ofcourse,worldwide.Suspendedparticleshavebeenblamedformostemittermalfunction,buttheymayparticipateonlyindirectlyinthecloggingprocess.Frequently,thesmall,suspendedparticlesarecaughtbythefilamentandslimeby-productsofbacteriaandincreaseinsizetocauseemitterplugging.Thus,thecontrolofmicroorganismswouldhelpgreatlyinalleviatingemitterplugging.
Asurprisingobservationduringourinvestigationsondeterminingthecausesofemittercloggingwasthepresenceoflargequantitiesofmicroscopictosand-sizeplasticmaterialsobstructionemitteropenings.Theplasticcuttingsoriginatefromthesawingofthepipesduringtheinstallation,modificationorrepairofthedripsystem.Thisproblemcanbereadilycorrectedbycuttingthepipeortubingwithspeciallydesignedcuttersthatdonotformplasticparticles.Whensawingisnecessary,cleaningandflushingoftherepairedsectionsbeforetheyarereconnectedintotheconveyancesystemcanreduceplugging.Otherunusualobstructionswerethepresenceofoilandgreaseparticlesfromleakageofbearingsealsofwellandboosterpumpsthatareconnecteddirectlyintothedripsystem.Theobvioussolutioninthiscaseisthepropermaintenanceofthelubricantseals.Also,thesteelcasingofwellswasobservedtobethesourceofdissolvediron,whichisformedbyiron-reducingbacteria.Emittercloggingpreventioninsuchinstanceinvolvesthecontrolofthebacterialcontaminationortheuseofplasticinsteadofsteelcasing.
Abriefcommentshouldbemadeonthepresenceofsnailsinthedriplines.Theadultsnailscanbereadilyremovedfromthewaterbysimplefiltration.However,theireggsorlarvaecanpassthroughfiltersandeventuallymaturetotheadultformintheirrigationlineandcauserestrictedwaterflowintheemittersandlarger-sizedtubing.Otherorganismsthatcanpassthefiltersandundergosimilarmetamorphismorincreaseinpopulationorsizewouldalsocreatecloggingproblems.
Rootintrusionintoemitteropeningsandtubingthatrestrictwaterflowhasbeenobservedforsometypesofburiedtubing(Bui1988;KinoshitaandBui1988).Emitterplugginginthiscaseisnotcausedbyirrigationwaterquality.
Waterqualityevaluationandclassification
Basedonthefindingsonemittercloggingandexperiencegainedincontrollingit,investigatorshavederivedaclassificationschemethatincludedthemajorfactorsinvolvedinemitterclogging.Thisisrelatedtoirrigationwatercomposition(Table2).Suchaclassificationcanbeusedasaguideforidentifyingpotentialclogginghazardaswellasforselectinganddesigningwatertreatmentsystems.Littlechangeintheclassificationschemehasbeenmadesinceitsproposalintheearly1980's.
Exceptpossiblyformicrobialpopulationanalysis,measurementsofsuspendedloadandchemicalcompositioncanbemadebytheoperatorormostagriculturalservicelaboratories.Theeffectoffertilizerorotherchemicalsontheirrigationwaterthatmaycreatecloggingproblemscanbetestedbytheoperatorbytreatingthewaterwiththeadditive(GilbertandFord1986).Testscanbeperformedinthelaboratoryoroffice,independentofthedripsystem,sothatthesystemwillnotbeadverselyaffectedifanynegativeresultsareobtained.AnyfertilizerorchemicaladditivethatincreasesthepH(alkalinity)ofthewatertothepointwherecarbonate,phosphateorhydroxidecanprecipitateshouldbeavoided.
Table2.Waterqualityclassificationrelativetoitspotentialfordripemitterclogging(Bucksetal.1979)
Rolstonetal.(1986)developedcriteriaforfertilizerapplicationindripsystems.Intheirpresentation,theyconsiderthesolubilityofthefertilizerandtheinteractionsofthefertilizerwiththedissolvecomponentsintheirrigationwater.Sincethen,acidifiedformsofnitrogenandphosphorushavebecomeavailable(urea-sulfateandurea-phosphate),whichhavelesstendencytocauseprecipitationproblemsthanearlierfertilizerformulations(MikkelsenandJarrell1987).
Waterswithhighconcentrationsofsulfideanionscancauseironprecipitation.Ironandmanganesesulfidesareveryinsolubleeveninacidsolutions.Thedissolvedsulfideanioncanalsoreactwithactivechlorinewhenthewaterischlorinatedsothattheeffectivenessofthechlorinationisreduced.Thus,thechlorinationrequirementofsuchwaterishigherthanthatofthetypicalnon-sulfideirri