irrigationnz resource book 2: irrigation glossary
TRANSCRIPT
ContentsGeneral irrigation terminology 1
Irrigation 1
Soil water terminology 5
Soilwaterstorage 5
Soilmoisturestatus 6
Combinedterms 7
Soilwatermovement 8
Soilwaterpotential 9
Soilwatercontent 10
Plant water use 11
Irrigation application 12
Irrigation scheduling 13
Regulatory terms 14
Calculations 17
Conversions 18
ThisbookispartofaseriesprovidingacomprehensivetrainingresourceforirrigationindustryparticipantsinNewZealand.
Itisacomprehensivecatalogueofthecommonterminology,acronyms,conversions,andotherusefulinformationusedintheirrigationindustry.
ISBNNumbers:Printed: 978-0-473-24109-4PDF: 978-0-473-24110-0
Compiledby:D.J.Bloomer,A.CurtisandP.Reese.
AcknowledgmentstoBrentClothier,CarolynHedley,IanMcIndoe,SamCarrick,SteveGreen,TrevorWebbandValSnowforcontributions.
©IrrigationNewZealand2013
SupportedbySustainableFarmingFund
1|IRRIGATION GLOSSARY
General irrigation terminologyIrrigation The action of applying water to land in order to supply plants with necessary water replacing moisture lost through evapo-transpiration.
Annual cost Theoperatingcosts(energy,labour,maintenance)plusthecostofcapital(exclusiveofGST).
Aquifer Undergroundlayerofwaterbearingrockorunconsolidatedmaterialsuchasgravelorsands.
Average annual precipitation Long-termhistoricyearlyaverage(generally30yearsormore)ofprecipitation(rain,snow,dew)receivedbyanarea.
Back flow preventer Devicedesignedtopreventwaterfromflowinginreversethroughthesystem.Commonlyusedtopreventaddednutrients,chemicalsoreffluentfrommixingwithcleanwatersources.
Bore Adrilledholeaccessingundergroundwater.
Capital cost Theoverallsystempurchaseandinstallationcost.
Cavitation Theformationandthenimmediatecollapseofvacuumcavitiesinaliquid.Usuallyoccurringwhentheliquidissubjectedtorapidchangesofpressure.
Chemigation Applicationofchemicalstocropsthroughanirrigationsystem.Thisisdonebymixingthemwiththeirrigationwater.
Deficit irrigation Irrigationwatermanagementoptionwherethesoilintheplantrootzoneisnotrefilledtofieldcapacityinallorpartofthefield.
Design specification Adocumentthatdefinessite-specificperformancetargetsthataproposedirrigationsystemmustbeabletoachieve.Adesignerpreparesthefinaldesigntomeettheserequirements.Adesignspecificationincludessuchfactorsas:
• Systemcapacity
• Applicationdepthrange
• Maximumapplicationintensity
• Minimumdistributionuniformity
• Returninterval.
Distribution efficiency Ameasureofhowmuchofthewatersuppliedtothepropertyreachestheapplicationsystem.Itisafunctionoflossesintheconveyanceordistributionsystem,fromthepointofwaterabstractionorentrytotheproperty(inthecaseofirrigationschemes)totheapplicationsystem.
2 | IRRIGATION GLOSSARY
GENERAL IRRIGATION TERMINOLOGY
Effective root depth Thedepthofsoilprofilethathasenoughrootingdensityforextractionofavailablewater.Rootsmaybefoundatdepthsgreaterthanthisvaluebutdonotcontributesignificantlytowaterextraction.
Equivalent applied depth Indrip-microirrigation,determinedfromthevolumeappliedtoaplant,adjustedfortheallocatedgroundareaperplant.
Fertigation Applicationofnutrientsthroughanirrigationsystem.Thisisdonebyinjectingthemintotheirrigationwater.
Flow (flow rate) Measurementofthevolumeofwaterpassingapointinagiventime.E.g.litrespersecond,cubicmetresperhour.
Friction loss (head loss) Amountofpressurelostthroughpipesduetowatermovementandturbulence.
Head (pressure) Commonlyusedasatermforpressure.Oftenreportedastheequivalentheightofawatercolumnmeasuredinmetres.Conversiontopressureunitsaccountsforthespecificgravityofwater(about9.81m/s)so10mheadisequivalenttoabout98.1kPa.Formanypurposes,anapproximationof10m=100kPaor1barisused.
Head (flow) Historictermforflowrelatedtominingrights.[1head=1cubicfootpersecond=28.32litrespersecond]
Headworks Describesthestartoftheirrigationdistributionsystem.Itcontainsexposedmainlines,pumps,valves,filters,meters,monitoringandtelemetryequipmentnecessarytorunthesystem.
Headworks efficiency Ameasureofthehydraulicperformanceoftheintakestructure,pumpandheadworks(excludingpumppressureandelevationdifferences)toindicatetheextentofpressurelossinthewatersupplysystembetweenthewatersupplypointandthemainlineentry.
Hydraulic efficiency Ameasureofthesystemhydraulicperformance;measuringpressurelostbetweenthedelivery(mainlineentry)anddischargepoints(machineentry,hydrant,ortake-offindrip-microsystems),excludingvariationsinelevation.
infiltration gallery Acoarsefiltrationsystematpointoftakefromwatersource.Maybeconstructedofarockorgravelbarrierwithorwithoutembeddedsteelmeshdrumstoaidthepassageofwater.Surfacewaterpassesthroughintoachannel,pondorpipe.
infiltrometer Deviceusedtomeasuretheinfiltrationrate/intakerateofwaterintosoil.Aringinfiltrometerconsistsofmetalringsthatareinserted(driven)intothesoilsurfaceandfilledwithwater.Therateatwhichwaterentersthesoilisobserved.
irrigation schedule Procedureofestablishingandimplementingthetimeandamountofirrigationwatertoapply.Determiningwhentoirrigateandhowmuchwatertoapply,baseduponmeasurementsorestimatesofsoilmoistureorcropwaterusedbyaplant.Setofspecificationsidentifyingtimestoturnonandoffwatertovariouszonesofanirrigationsystem.
Figure 1. Headworks.
GENERAL IRRIGATION TERMINOLOGY
3|IRRIGATION GLOSSARY
Lysimeter Deviceformeasuringdeeppercolationfromasoilprofile.Consistsofanenclosedvolumeofundisturbedsoilwithsomemeansofcollectingdrainagewater.Itmayalsoincludesomemethodtomeasurechangesinthevolumeofstoredsoilwater.
Mainline Apipelinethatcarrieswaterfromsystemheadworkstooff-takessupplyingaseriesofblocks.
Management zone Adiscreteareawithaparticularsetofirrigationmanagementneedsrelatingtospecificfactors,suchastopography,soil,crop,systemormanagementdifferences.
Non-point source pollution (Diffuse pollution) Pollutionoriginatingfromdiffuseareas(landsurfaceoratmosphere)havingnowell-definedsource.
Performance curve Graphshowingthecapabilityofaproductwithvaryinginputs.i.e.thedynamicheadofapumpasitvarieswithdischarge.
Pressure loss Amountofpressurelostaswaterflowsthroughasystem.
Pressure rating Estimatedmaximuminternalpressurethatcanbecontinuouslyexertedinapipeorcontainerwithahighdegreeofcertaintythatitwillnotfail.
Pressure regulator Devicewhichmaintainsconstantoperatingpressure(immediatelydownstream)whichislowerthantheupstreampressure.
Pressure tank Anairtightcontainerwithapressurisedairpocketorbladderattachedtoawatersystemsothatitbehavesasatemporarypressurisedwatersupply.
Return on water use Themarginalchangeinreturnsresultingfromtheirrigationsystem.Itisgenerallybasedonmeanannualirrigationdemand,andincorporatescostandproductivityelements.Valuescanbeexpressedasreturnsperunitareaorvolumeofwater($/haor$/m3).Valuescanbepositiveornegative,dependentonsystemcosts,productivityandcropreturns.
Soil bulk density Themassofdrysoilperunitofbulksoil–themassofsoilinaknownvolumeasextractedfromtheground.Thebulkdensityofsoildependsonitsmineralmakeupandthedegreeofcompaction.
Soil horizon Layerofsoilorsoilmaterialapproximatelyparalleltothelandsurfaceanddifferingfromadjacentlayers.Differencescanbephysical,chemical,andbiologicalpropertiesorcharacteristicssuchascolour,structure,texture,kindsandnumberoforganismspresent,degreeofacidity,etc.
Soil profile Averticalsectionthroughthesoilfromsurfacetobelowtherootzone.Asoilprofileiscomprisedofoneormoresoilhorizons.
Soil structure Combinationorarrangementofprimarysoilparticlesintosecondaryunitsorpeds.Thesecondaryunitsarecharacterizedonthebasisofsize,shape,andgrade(degreeofdistinctness).
Soil texture Relativeproportionsofsand,siltandclayinasoil.
Figure 2. Pressure gauge.
4 | IRRIGATION GLOSSARY
GENERAL IRRIGATION TERMINOLOGY
Submersible pump Apumpthatoperateswhilesubmergedinacolumnofwaterdownaboreorwell.
Surface water body Anysignificantaccumulationoffreshwaterthatisvisibleonthesurfaceoftheearth.Surfacewaterbodiesincludelakes,rivers,streams,wetlands,waterraces,watercourses,anddrains.
System capacity Theflowofwaterperunitofirrigatedareanormallyexpressedaslitrespersecondperhectare(L/s/ha)ormmperday(mm/d)calculatedonthebasisofthesystemoperating24hoursperday.
Operating system capacityTheflowofwaterperunitofirrigatedareathatcanbesuppliedinthetimethatthesystemisoperating.
Potential system capacityThemeandailyflowofwaterperunitofirrigatedareathesystemisabletoprovideinthetimeavailableforirrigation.
Pumping rate Thevolumeofwaterperunittime(l/sorm3/hr)thatapumpisdesignedtodeliveratthedesignpressure.
Required system capacity Theflowofwaterperunitofirrigatedarearequiredtoreplacewaterusedbythecrop(plusanyadditionalamountsforotherpurposes)inthetimeavailable.
System specification Asystemspecificationisadocumentthatdescribeswhatthefinalirrigationsystemwillcompriseof,andwhatitwillbecapableofachieving.
Asystemspecification:
• listscomponentsofthesystem,e.g.,pipesandpumps
• showstheirlocations,and
• describestheirkeyspecifications,e.g.,diameters,speeds,pressures.
Tensiometer Instrumenttomeasurethemoisturecontentofsoil.Consistingofaporouscupfilledwithwaterandconnectedtoamanometer,vacuumgauge,orpressuretransducerusedformeasuringthesoil-watermatricpotentialorvacuumtension.
Thrust block Concreteorsolidblocksplacedinpipingsystemsatchangesindirectionofwaterflow(tees,corners)topreventmovementofthepipe.
Water hammer Shockwavecreatedwhentheflowofwaterinapipingsystemsuddenlystops(orchangesspeed),usuallytheresultofafast-closing(oropening)valve.
Water table Uppersurfaceofasaturatedzonebelowthesoilsurfacewherethewaterisatatmosphericpressure.
Weir Flowmeasuringdeviceforopen-channelflow.Weirscanbeeithersharp-crestedorbroad-crested.Flowopeningmayberectangular,triangular,trapezoidal,orspeciallyshapedtomakethedischargelinearwithflowdepth.
Yield Flowratethatisachievablefromanaquifer.Thisisdependentonthehydraulicconductivityoftheaquifermaterial.
Figure 3. Submersible pump and motor.
5|IRRIGATION GLOSSARY
Soil water terminologySoil water storageA number of terms are used to describe the status of soil moisture or soil water content. Many have been used interchangeably, or in conflicting ways by different authors.
Irrigation New Zealand recommends that the following terms and associated calculations are used to describe the amount of water in soil.
KEY TERMS
Content Thevolumetricwatercontentofsoilasmeasuredatapointintime(m3water/m3soil,mmwater/mmsoil).
Capacity Thepotentialofsoiltoholdwater,describedasaratioofvolumetricwatercontentintegratedoveradepthofsoil(m3water/m3soil).Thedepthwillbespecifiedascentimetressoildepth.
Depth Therainfalldepthequivalentofwaterinadefineddepthofsoil(mm).
Water holding capacity (WHC) Thevolumetricratioofallwatercontainedinalayerordepthofsoilatfieldcapacity,includingthatheldtootightlyforplantstoaccess.
Total available water (TAW) Allthewaterthatisextractablebyplants(planttypemaybespecified);takenasthedifferencebetweensoilwateratfieldcapacityandatpermanentwiltingpoint.
Readily available water (RAW) Thewaterthatisextractablebyplants(planttypemaybespecified)withoutgrowthlimitationtakenasthedifferencebetweensoilwateratfieldcapacityandatstresspoint.
Stress available water (SAW) Thewaterthatisextractablebyplants(planttypemaybespecified)butwithgrowthlimitationtakenasthedifferencebetweensoilwateratstresspointandatpermanentwiltingpoint.
6 | IRRIGATION GLOSSARY
SOIL WATER TERMINOLOGY
Soil moisture statusSaturation Soilissaidtobesaturatedwhenallitsporesarefullofwater
andnoairisleft.Mostplantsdonottoleratesaturatedsoilsforlongasoxygenintherootzoneisessential.
Field capacity (FC) Thesoilmoisturecontentaftergravitationaldrainageslowsfromasaturatedconditiontoaratethatisinsignificant(i.e.drainageratelessthan1mm/day).
Thisisusuallyestimatedinthefieldbymeasuringthesoilwatercontent2–3daysafterheavyrainfall,orbymeasuringthewatercontentofsoilcoresinthelaboratoryaftertheyhavebeenequilibratedatasoilmatricpotential.
InNewZealandthelaboratoryestimationoffieldcapacityismeasuredatthenominal-10kPasoilmatricpotential,butdirectfieldmeasurementsshowthatitcanvarybetween-2kPato-30kPadependingonsoiltexture.
Stress point (SP) Thesoilmoisturecontent,belowwhichplantgrowthbeginstoslow.
Thispointisdifferentfordifferentplants.Moisturestressisstronglyrelatedtosoilmatricpotential,andgenerallyoccursatapproximately-50kPa.Howeverlabmeasurementscommonlyuse-100kPasoitisimportanttofindoutthecorrectvalueforparticularsoilsinthefield
Itisoftenrelatedtowatercontentforirrigationmanagementpurposes.Asaruleofthumbmostplantswillbecomestressedwhenabout50%ofthe‘totalavailablewater’hasbeenused.
Permanent wilting point (WP)Thesoilmoisturecontentwhereplantgrowthstops.
Thisisthelowerlimitofavailablewaterbelowwhichplantgrowthceasescompletely.Thesoilmatricpotentialatthispointcorrespondstoabout-1,500kPa(-15bar).The‘permanentwiltingpoint’isgenerallygovernedbytheamountofclayinthesoil–thegreatertheamountofclay,thehigher(%soilmoisture)the‘permanentwiltingpoint’.
Oven dry Somewaterissotightlyheldbythesoil,itisunavailableforplants.This“hygroscopic”watercanonlyberemovedbysun-baking,orinalabbyovendryingsoilat105˚celsiustoconstantweight.
7|IRRIGATION GLOSSARY
SOIL WATER TERMINOLOGY
Combined termsProfile available water (depth) (PAWD)
Therainfallequivalentdepthof‘totalavailablewater’withinaspecifieddepthinthesoil.
Thesoildepthincentimetresisshownasasubscriptfollowingtheacronym;e.g.PAW60isthe‘profileavailablewater’inagivensoiltoadepthof60cm.Itissoilspecificandindependentofplanttypeorrootdepth.
Profile readily available water (depth) (PRAWD)Therainfallequivalentdepthof‘readilyavailablewater’withinaspecifieddepthofsoil.
Thesoildepthincentimetresisshownasasubscriptfollowingtheacronym;e.g.PRAW40isthe‘readilyavailablewater’inagivensoiltoadepthof40cm.Itissoilspecificandindependentofplanttypeorrootdepth.
Crop available water (depth) (CAWD)Therainfallequivalentdepthof‘totalavailablewater’byaspecifiedcropfromitsrootzone.
Therootzonedepthincentimetresisshownasasubscriptfollowingtheacronym;e.g.CAW40isthe‘cropavailablewater’inthe40cmdeeprootzoneinagivensoil.
Readily available water (depth) (RAWD)Therainfallequivalentdepthof‘readilyavailablewater’byaspecifiedcropfromitsrootzone.
Therootzonedepthincentimetresisshownasasubscriptfollowingtheacronym;e.g.RAW40isthe‘readilyavailablewater’inthe40cmdeeprootzoneinagivensoil.
Soil moisture deficit (depth) (SMDD) Therainfallequivalentdepthofwaterrequiredtoreturnthesoilwatercontentintherootzonefromitscurrentstatusto‘fieldcapacity’.
Therootzonedepthincentimetresisshownasasubscriptfollowingtheacronym;e.g.SMD40isthe‘soilmoisturedeficit’inthe40cmdeeprootzoneinagivensoil.
Non-limiting water range (NLWR)Representstherangeofwatercontentinthesoilwherelimitationstoplantgrowth(suchaswaterpotential,air-filledporosity,orsoilstrength)areminimal.
• Theupperlimit(wetend)ofnon-limitingwaterrangeisdeterminedbywatercontentat‘fieldcapacity’,andadequateaerationforplantroots(usuallytakenasaminimumairfilledporosityof10%).
• Thelowerlimit(dryend)isdeterminedby‘permanentwiltingpoint’andtheabilityofrootpenetration.Rootpenetrationismeasuredassoilmechanicalresistancetakenatanarbitraryvalue,oftenpenetrationresistanceof3MPa.
Figure 4. Crop and irrigator.
8 | IRRIGATION GLOSSARY
SOIL WATER TERMINOLOGY
Soil water movementBypass flow (Preferential flow)
Watermovingdownthroughlargeporesorcracksinthesoilprofilewithoutbeingabsorbedintoit.
Drainage Thelossbydownwardflowofexcesswaterfromsaturatedporespacesinsoil.Itcanbereducedorstoppedbyslowlyorimpermeablelayerswithintheprofile,orbyhighwatertables.
Groundwater recharge Includesalldrainage,whetherfromirrigationorprecipitation.Itisestimatedfromthebalanceofwaternotretainedintherootzone,calculatedafteranysurfacelosseshavebeenaccountedfor.
infiltration rate Themovementofwaterintothesoilprofile.Measuredastherate(mm/hour,mm/day)atwhichasoilabsorbswater.Itvarieswithsoiltype,soilsurfaceconditionandmoisturecontent.
Leaching Thelossofsolublematerial,chemicalormineral,throughdrainage.Measuredasaconcentration(mg/litre)orasaloadingorarate(kg/ha/year).Loadingisdeterminedbyintegratingconcentrationanddrainage.
ThetermcanalsocoverthelossofothermineralsandsubstancesthataretransportedbutnotdissolvedforexampleEcoliandphosphorous.
Percolation Thedownwardmovementofwaterthroughthesoil.Measuredasarate(mm/hour,mm/day).
Permeability Theabilityofairandwatermovementthroughthesoil.Itaffectsthesupplyofroot-zoneair,moisture,andnutrientsavailableforplantuptake.Asoil’spermeabilityisdeterminedbytherelativerateofmoistureandairmovementthroughthemostrestrictivelayer.Itisoftenmeasuredasarate(mm/hour,mm/day).
Surface ponding Waterthatdoesnotimmediatelyinfiltrateintothesoilbutcollectsatthelowpointsinthemicro-topographyofthesoilssurface.Theimplicationsofsurfacepondingarecomplex,dependingonbothtimeandextentofponding.
Surface runoff Waterthatdoesnotimmediatelyinfiltrateintothesoilandinsteadleavesthetargetzonebyrunningoffacrossthesoilsurfaceundergravity.
9|IRRIGATION GLOSSARY
SOIL WATER TERMINOLOGY
Soil water potential The amount of water that is stored and is available to plants, and how freely water drains, are processes governed by potential energy. Potential energy differences determine storage and redistribution within soil. A potential energy gradient dictates soil moisture redistribution and losses, as water moves from areas of high- to low-potential energy.
Critical concepts are soil water potential and soil water content.
Soil water potential Waterpotentialisthepotentialenergyofwaterperunitvolumerelativetopurewaterinreferenceconditions.Itquantifiesthetendencyofwatertomovefromoneareatoanotherduetoosmosis,gravity,mechanicalpressure,ormatrixeffectssuchassurfacetension.Waterpotentialintegratesdifferentpotentialdriversofwatermovement,whichmayoperateinthesameordifferentdirections.
Gravity potential Theforcegravityhasonwater;thegreatertheheightofwater,thegreaterthegravitationalpotential.Gravitationalpotentialismeasuredastheheightaboveareferencepoint.Ifthereferenceisthesoilsurfaceandthereare100mmofwatersittingonthesoilsurface,thegravitationalpotentialisequalto100mm.Gravitationalpotentialisakeydriverofrapidsoildrainage.
Matric potential (Matrix potential) Thesurfaceattractionsoilparticleshaveforwater.Ifadrysoilisadjacenttoapoolofwater,thesoilwillabsorbthewater.“Free”orstandingwaterhasanenergylevelofzero.Thematricpotentialofunsaturatedsoilislessthanzerosoiswrittenasanegativevalue.
Themagnitudeofmatricpotentialdependslargelyonsoilporosityandchemicalmake-up.Asasoildries,thematricpotentialbecomesmorenegativeasthesoilwaterbecomesmoretightlyheldbythesoilinsmallerpores,andisharderforplantstoextract.
Matricpotentialcanbemeasuredwithatensiometer.Electricalresistanceblocksmaybeusedindriersoilswheretensiometersmaynotwork.
10 | IRRIGATION GLOSSARY
SOIL WATER TERMINOLOGY
Soil water contentSoil water content is the amount of water present in the soil. It can be measured as relative weight or relative volume. Both can be described as fractions or percentages (weight for weight, volume for volume) but are actually quite different.
Gravimetric water content Theweightofwaterinagivenweightofsoil(g/gorkg/kg).Weighingofbothsoilandwateriseasy,butdifferingsoilbulkdensitiesmakesinterpretationforirrigationmanagementdifficult.
Todeterminegravimetricwatercontent,asoilsampleisweighed,thendriedandre-weighed.Gravimetricwatercontentistheweightofwaterremovedfromthesoildividedbytheweightofdrysoil.
Thestandardlaboratorymethodinvolvesplacingafieldmoistsoilsampleinanovenat105˚celsiusuntilweightisconstant.Calculatingthedifferenceinweightbetweenthewetsoilandthedrysoildeterminestheweightofwaterremoved.Thedrysoilweightistheweightofsoilusedinthecalculation.
Volumetric water content Thevolumeofwaterinavolumeofsoil.Itisthegravimetricwatercontentadjustedbythesoilbulkdensity.
Todeterminevolumetricwatercontent,aknownvolumeofsoilisweighed,driedandre-weighed.Thevolumetricwatercontentisthevolumeofwaterremoved(1mlofwaterweighs1gm)dividedbythevolumeofsoil.
Volumetricwatercanbedescribedasdepthofrainfalland/orirrigationequivalentinacertaindepthofsoil(e.g.therootzone).Thisisveryusefulfordeterminingthesupplyavailableforplants,whenirrigationisneededandhowmuchshouldbeapplied.
11|IRRIGATION GLOSSARY
Plant water useEvaporation Thelossofwaterintotheatmospherefromsoil,waterand
plantsurfaces.
Transpiration Thelossofwaterthroughstomata(pores)ofleafsurfaceswhichallowgasexchangeforphotosynthesisandrespiration.Transpirationhelpscooltheplantanddrawupnutrients.
Evapo-transpiration (ET) Thecombinedprocessesofevaporationandtranspiration.
Potential evapo-transpiration (PET)Theamountofwaterthatwouldbelostthroughevaporationbyahealthyshort,uniform,activelygrowingindicatorcropthatfullycoversanareaandisnevershortofwater.
Crop evapo-transpiration (ETcrop) Theactualwaterusebyacropofinterest.ItmaybemeasuredorcalculatedfromPETandacropfactor.
Crop factor Theadjustmentusedtorelatethelossofwaterbyevapo-transpirationbyanactualcrop,tothatofatheoreticalindicatorcrop,(normallyfullcover,uniformpasture).Itisinfluencedbyspecies,growthstage,groundcoverorcanopyareaeffects.
Crop irrigation demand (CiD) Theamountofwaterpotentiallyconsumedbytheirrigatedcropinoneweekduringpeakevapo-transpirationconditions(mmorm3/ha/week)
Moisture stress Occurswhenthewaterinaplant’scellsisreducedtolessthannormallevels.Reasonsforthisincludealackofwaterintheplant’srootzone,higherratesoftranspirationthantherateofmoistureuptakebytheroots,orlossofrootsduetotransplantation.Moisturestressismorestronglyrelatedtowaterpotentialthanitistowatercontent.
Matricpotentialsareveryimportantforplantwaterrelations.Strong(verynegative)matricpotentialsbindwatertosoilparticleswithinverydrysoils.Plantsthencreateevenmorenegativematricpotentialswithintinyporesinthecellwallsoftheirleavestoextractwaterfromthesoilandallowphysiologicalactivitytocontinuethroughdryperiods.
Potential soil moisture deficit (PSMD)Ameasureofmoisturestressexperiencedbyacrop.Seasonal‘potentialsoilmoisturedeficit’iscalculatedfromsoilmoisturebudgetsbysummingalldeficitsbelowthecriticaldeficit(orMAD)duringthegrowingseasonforthecrop.
Root zone Thepartofthesoilprofileinwhichactiverootsarepresent,andfromwhichwaterandnutrientscanbeextractedbytheplant.
Figure 5. Emerging crop.
12 | IRRIGATION GLOSSARY12
Irrigation applicationApplication depth Therainfallequivalentdepthofwaterappliedtothesoil
surfaceduringasingleirrigationevent.Itisthedepthofwaterthatwouldbecaughtinaraingauge,notthedepthofsoilthatiswetted.
Application intensity Therate(mm/hour)atwhichirrigationisapplied.Itcompares“gentleshowers”with“heavyrain”.(Seespecificcalculationsbelow).
instantaneous application intensity (Ri) Therate(mm/hr)atwhichirrigationisappliedbyanindividualstream,fromanindividualoutletornozzle,toaverysmallarea.Forexample,forarotatingboomitistheflowfromasingleoutletdividedbytheareabeingwettedatanyinstantbythatoutlet.
Average application intensity (Ra) Therateofapplication(mm/hr),averagedovertheindividualapplicator’swettedfootprint.Forexample,forarotatingboomitistheapplicator’sflowratedividedbytheareawettedbyonefullrotationoftheboom.
Application rate Thecommonlyusedtermforthemorecorrecttermapplicationintensity(ie.heavythunderstormvslightdrizzle).
Note:Itdoesnotmeanapplieddepthperevent(seeApplicationdepth)orapplieddepthperday(seeSystemcapacity).
Application efficiency Thepercentageofappliedwaterthatisretainedintherootzone,orinthetargetarea,afteranirrigationevent.
Application uniformity Thespatialvariability(measureoftheevennessofcoverage)oftheapplicationbyirrigation.Itcanbedefinedinavarietyofways.Commonexamplesare:
• DistributionUniformity(DU)
• CoefficientofUniformity(CU)
• CoefficientofVariation(CV)
Distribution uniformity (DU)Onemeasureofapplicationuniformity.Itiscommontouselowquartiledistributionuniformity(DULQ),whichcomparestheaverageofthelowestquarterof(measured)applieddepthswiththeaveragedepthofall(measured)applieddepths.
Low quarter irrigation adequacy Theratioofthemeanlowquarterdepthapplied,tothemeantargetdepthrequiredacrossthefieldasawhole.
Mean field application depthMeanapplicationdepthcollectedalongtransverselinesafteradjustmentforevaporationandoverlapfromadjacentstrips.
Figure 6. Micro sprinkler.
13|IRRIGATION GLOSSARY
Irrigation schedulingirrigation requirement Thecropwaterrequirementplusanyadditionalbeneficialwater
requirementlessreceivedprecipitationandstoredsoilmoisture.
Management allowed depletion (MAD)TheproportionoftheCropAvailableWaterthatisallowedtoberemovedbeforeirrigationisapplied.Thelevelisamanagementdecisiondependentoncroptype,stageofcropdevelopment,seasonalwaterdemandandothermanagementfactorsandconstraints.
Note:thistermisnottobeconfusedwithmaximum allowable deficitwhichisanothertermforthetriggerpointseebelow.
Return interval (Return period)Thetypicalperiodbetweenoneirrigationeventandthenext.Itisusuallycalculatedforthemostdemandingperiodsothattheirrigationsystemcanmeetwaterdemandmostofthetime.
Scheduling co-efficient Usedtodeterminehowmuchextrairrigationshouldbeappliedtoensurethatmostofthecropgetssufficientwater.Itaccountsforvariancesandinefficienciesofapplicationsystems.
ItiscommontousethereciprocalofthelowquartileDistributionUniformitytocalculatetheextrarequired.Multiplyingirrigationneedbytheschedulingcoefficientdeterminesatargetapplicationdepththatensuresthat7/8thofthecropwillreceiveatleasttherequireddepthofirrigation(somewillgetconsiderablymore).
Scheduling coefficient for effluent Whenapplyingeffluenttothesoil,thereisaneedtoavoidover-application,ratherthanunder-applicationasisthecasewithnormalirrigation.Theschedulingcoefficientcanbeusedtodeterminehowmuchtoreduceaverageeffluentapplicationtoensure7/8thgetslessthanthetargetnutrientofwaterdose.
Shoulder periods Thebeginningandendoftheirrigationseason(typicallyearly/midspringandautumn)whendemandisnotasgreatbecauseofthelowerETandincreasedlikelihoodofrainfall.
Soil moisture deficit Thedifferencebetweenthesoilwatercontentatfieldcapacityandthecurrentsoilwatercontent.Itismeasuredinmillimetresofrainfallequivalentintherootzone.
Target depth Themeanapplieddepthchosentobeapplied.
Itwillnormallybelessthanthesoilmoisturedeficitatthetimeofapplicationtoallowspaceforanysubsequentrainfall.Itmaybeincreasedtoaccountfornon-uniformapplication.
Trigger Point (irrigation point, Critical deficit, Maximum allowable deficit) Thesoilmoisturecontent(mm)ormatricpotential(kPa)atwhichirrigationisdeemednecessarytoavoidplantstress.
Figure 7. Scheduling.
14 | IRRIGATION GLOSSARY
Regulatory terms1 Abatement notice RequirescompliancewiththeRMAwithinthetimespecified
inthenotice.Onlycouncilscanissuethesetogetsomeonetostoportostartdoingsomething.
Applicant Aperson,groupororganisationwhoappliedforaresourceconsent.
Assessment of environmental effectsAreportthatmustbegiventothecouncilwithyourresourceconsentapplication.Itoutlinestheeffectsthattheproposedactivitymighthaveontheenvironment.
City or District councils Areprimarilyresponsibleformanagingtheenvironmentaleffectsofactivitiesonland.
Department of Conservation (DoC)AdministerslandundertheConservationandNationalParksActsandhasaroleundertheRMAoverseeingthemanagementofthecoastalenvironment.
Designations Provisionsinadistrictplanwhichprovidenoticetothecommunityofanintentionbythecouncilorarequiringauthoritytouselandinthefutureforaparticularworkorproject.
District plans PreparedbycityordistrictcouncilstohelpthemcarryouttheirfunctionsundertheRMA.
Enforcement order AwayofgettingsomeonetocomplywiththeRMA.Itdiffersfromanabatementnoticeinthatanybody(notjustthecouncil)canapplyforanenforcementorderagainstsomebodyelse.TheseareissuedbytheEnvironmentCourtratherthanthecouncil.
Environment Includes:
a. ecosystemsandtheirconstituentparts,includingpeopleandcommunities,and
b. naturalandphysicalresources,and
c. amenityvalues,and
d. thesocial,economic,aesthetic,andculturalconditionswhichaffectthemattersstatedinparagraphs(a)to(c)ofthisdefinitionorwhichareaffectedbythosematters.
Environment Court Specialistcourtwherepeoplecangotoappealdecisionsmadebycouncilsoneitherapolicystatementorplan,oronaresourceconsentapplication,orapplyforanenforcementorder.
1.www.mfe.govt.nz/rma/public/rma-terms.html
15|IRRIGATION GLOSSARY
REGULATORY TERMS
Further submission Providesanopportunityforpeopletocommentonotherpeople’soriginalsubmissionsonaproposedplan,planchangeorvariationeitherbysupportingoropposingthosesubmissions.
infringement notice Aninstantfinethatisissuedforrelativelyminorenvironmentaloffences.
Ministry for the Environment (MfE)Providesadvicetothegovernmentonpolicies,lawsandothermeanstoimproveenvironmentalmanagementinNewZealand.
National environmental standards (NES)Toolsusedtosetnationwidestandardsforthestateofanaturalresource.
National policy statement (NPS)Nationalpolicyguidanceformattersthatareconsideredtobeofenvironmentalimportance.
Plan change Theprocessthatcouncilsusetopreparechangestoanoperativeplan.
Private plan change Aplanchangeinitiatedbyanypersontoanoperativecouncilplan.
Project information memorandumIssuedbythecityordistrictcouncilandcontainsinformationrelatingtothelocationofthebuildingandwhetheritwillneedaresourceconsentornot.
Public notification Meansanoticepublishedinanewspaperornoticesenttoeverypersonthecouncilthinksmaybeaffectedbyaproposedplan,planchangeorvariation.
Publicly notified resource consent Meansthatanypersoncanmakeasubmissionontheconsentapplication.
Regional councils Primarilymanageresourcesliketheair,water,soilsandthecoastalmarinearea.
Regional plans Preparedbyregionalcouncilsiftheywanttousethemtohelpmanagetheresourcesforwhichtheyareresponsible.
Regional policy statements (RPS) Mustbepreparedbyallregionalcouncilsandhelpsetthedirectionforthemanagementofallresourcesacrosstheregion.
Resource consent Ispermissionfromthelocalcouncilforanactivitythatmightaffecttheenvironment,andthatisn’tallowed‘asofright’inthedistrictorregionalplan.
Resource Management Act 1991 (RMA) NewZealand’smainpieceofenvironmentallegislationandprovidesaframeworkformanagingtheeffectsofactivitiesontheenvironment.
16 | IRRIGATION GLOSSARY
Submission Outlinesyourwrittencomments,opinions,concerns,support,oppositionorneutralstanceaboutaproposeddevelopment,anoticeofrequirementforadesignation,oraproposedpolicystatementorplan.
Sustainable management Meansmanagingtheuse,developmentandprotectionofnaturalandphysicalresourcesinaway,oratarate,whichenablespeopleandcommunitiestoprovidefortheirsocial,economicalandculturalwellbeingandfortheirhealthandsafetywhile:
a. sustainingthepotentialofnaturalandphysicalresources(excludingminerals)tomeetthereasonablyforeseeableneedsoffuturegenerations,and
b. safeguardingthelife-supportingcapacityofair,water,soilandecosystems,and
c. avoiding,remedyingormitigatinganyadverseeffectsofactivitiesontheenvironment.
Unitary authorities Carryouttherolesofbothregionalanddistrictcouncils.
REGULATORYTERMS
17|IRRIGATION GLOSSARY
CalculationsAPPLiCATiON iNTENSiTY Applicationintensityiscalculatedbydividingtheflowratebythewettedarea,andadjustingtommapplieddepth,usingtheformula:
Rapp =3,600xQapp/Aapp
where:
Rapp =Averageapplicationintensity(mm/hr)
Q app =Flowratetotheapplicator(l/s)
A app =Wettedareaoftheapplicator(m2)
Thewettedareaoftheapplicatormustbedeterminedaccordingtothewettingpatternofthespecificirrigator.Ingeneralitistheareathatiswettedatagiveninstant,orinoneswingorrotationofaturningsprinkler,gunorboom.
individual sprinklersForindividualFDEsprinklers,Aappisthetotalareawettedbythesprinkler,andQappistheflowratetothesprinkler.Thisappliestoallindividualsprinklers,e.g.longlaterals,orseparateeffluentsprinklersattachedtopivotspans.
Multi-sprinkler linesForstationaryapplicatorswithmultiplesprinklers,Aappisthetotalareawettedbyallofthesprinklersontheindividualline,andQappistheflowratetothatline.
Rotating booms Forarotatingboomirrigator,Aappistheareawettedbyonefullrotationoftheboom,andQappistheflowratetothatmachine.
Gun irrigatorsForgunirrigators,Aappistheareawettedbyoneswingofthegunacrossitsoperatingarc,andQappistheflowratetothatmachine.Thisappliestoallgunirrigators,e.g.,atravellinggun,oreffluentgunattachedtoacentre-pivot.
Travelling boom or linear move Fortravellinglinearsystem,Aappisthetotalareawettedbyallofthesprinklersonallspanswhenthemachineisstationary,andQappistheflowratetothemachine.
Separate systems attached to centre-pivots ForsystemswhereaseparateFDEapplicatorisattachedtoacentre-pivot,theapplicationintensityiscalculatedasiftheFDEapplicatorwereoperatingasaseparateunit,e.g.astationarysprinkler,oragunirrigator(asabove).
18 | IRRIGATION GLOSSARY
ConversionsVOLUMES1cubicmetre=1,000litres(1m3=1,000L)
1megalitre=1,000cubicmetres(1ML=1,000m3)
1litreis100mmx100mmx100mmor0.1mx0.1mx0.1m
1litrespreadover1squaremetreis1millimetredeep(1L=1m2x1mm)
AREAS1hectare=10,000squaremetres(1ha–10,000m2)
Areaofcircle=Pixradiusxradius(A=∏r2)andPior∏=3.1416
FLOW1litrepersecond=3.6cubicmetresperhour(1L/s=3.6m3/h)
1head=1cubicfootpersecond=28.32litrespersecond(1head=28.32L/s)
1litrepersecondperhectare=86.4m3perdayperhectare=8.64millimetresperday
(1L/s/ha=8.64mm/d)or5mm/d=0.5787L/s/ha
PRESSUREThestandardpressureunitisthePascal.InirrigationitiscommontousethekilopascalorinsomecasesMegaPascalformeasurements.
1kiloPascal=1,000Pascals(1kPa=1,000Pa)
1MegaPascal=1000kiloPascals=1,000,000Pascals(1MPa=1,000kPa=1,000,000Pa)
1metreofwaterhead=about9.81kiloPascals(dependingonactualspecificgravityofwater)
ALTERNATiVE PRESSURE UNiTS1poundpersquareinch=about7kiloPascals(1psi=6.8948kPa)
1atmosphere=about101kiloPascals(1atm=101.325kPa)
1bar=100kiloPascalsorabout1atmosphere(1bar=100kPa=0.98692atm)
WATER POTENTiAL
Approx soil status Kilopascals (kPa) Megapascals (MPa) Bars Centibars
–1 –0.001 –0.01 –1
Field Capacity–10 –0.01 –0.1 –10
–33 –0.033 –0.33 –33
Stress Point–100 –0.1 –1 –100
–1000 –1.0 –10 –1000
Permanent Wilting Point
–1500 –1.5 –15 –1500
ONLiNE CONVERTERS
Therearefreeconvertersavailableeitheron-lineordownloadedtocomputersorsmartdevices.Theymakelifeveryeasy.Theapplication“Convert”byJoshuaMadisonisoneexample:http://joshmadison.com/convert-for-windows/
21|IRRIGATION GLOSSARY
NOTES
REFERENCESAllphotos©andcourtesyofDanBloomer,PaulReese,AndrewCurtisandAnnetteScott.
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