irrigationnz resource book 2: irrigation glossary

i|IRRIGATION GLOSSARY

Irrigation Glossary

BOOK 2

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.



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.



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.


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.


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.



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.



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.



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.



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.


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.


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.


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


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.


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


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).


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/


NOTES


NOTES

REFERENCESAllphotos©andcourtesyofDanBloomer,PaulReese,AndrewCurtisandAnnetteScott.

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irrigationnz resource book 2: irrigation glossary

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