Using Reference Evapotranspiration Data

http://edis.ifas.ufl.edu/ ( Publisher's URL )
MISSING IMAGE

Material Information

Title:
Using Reference Evapotranspiration Data
Physical Description:
Fact sheet
Creator:
Clark, GA
Publisher:
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication:
Gainesville, Fla.
Publication Date:

Notes

Acquisition:
Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status:
Published
General Note:
"First Published March 1993. Drip Tip No. 9304. Publication date: July 1994."
General Note:
"AE-251"

Record Information

Source Institution:
University of Florida Institutional Repository
Holding Location:
University of Florida
Rights Management:
All rights reserved by the submitter.
System ID:
IR00004504:00001


This item is only available as the following downloads:


Full Text

PAGE 1

FactSheetAE-251 July1994UsingReferenceEvapotranspirationData1 G.A.ClarkandC.D.Stanley2Referenceevapotranspiration(ETo)referstothe expectedwaterusefromauniformgreencovercrop surfacesuchasagrass.Actualcropuseisgenerally lessandisdeterminedbyusingacropcoefficient whichrelatescropET(ETc)toETo.Reported valuesofEToaregenerallyexpressedasinchesof wateruseoverthesurface.Thischoiceofunitsis appropriateforusewithsprinklerirrigationsystems. However,volumetricunitsmaybemoreappropriate forsubirrigation(seep)ormicroirrigation(dripor sprayjet)systems. ConversionofETovaluespresentedindepth units(suchasinches)tovolumetricunits(gallons)can helptheirrigationmanagerwithscheduling irrigations.Anacre-inchofwaterequalsavolumeof 27154gallons.ForexampleanETovalueof0.12 inchesperdayisroughlyequalto3260gallonsper acre[(0.12)(27154)].AveragedailyEToestimatesfor threeFloridaregionsareprovidedinTable1.The northernregionextendsfromOcalanorththroughthe panhandle,thecentralregionextendsfromOcala southtoFt.PierceontheeastcoastandSarasotaon theGulfcoast,andthesouthernregioncontainsthe remainingsouthernportionofFlorida.Valuesare expressedasinchesperdayandasgallonsperacre perday. Microirrigationsystemsapplywateringallonsper hourperunitlengthoftube,perdripemitter,orper sprayjetemitter.Therefore,irrigationzonesshould beassessedforsize(suchasacres,rollsofplastic, numberoftrees,etc.)andflowrequirements. Conversionswhichchangetheproductionareato hundredbed-feetperacre(HBFAC)wouldhaveunits compatiblewiththeapplicationratesofdriptubes (galsperminper100ftorgpm/100ft).Anacrehas 43560ft2ofarea.Therefore,dividethebedspacing (ft)into43560togetthenumberoflinearbedfeet peracre(LBFAC)andthendividethatvalueby100 togettheequivalentHBFACvalue.Forexample,a cropwithabedspacingof6fthasanassociated LBFACvalueof[(43560)/(6)=]7260andaHBFAC valueof72.6.Forcroprequirementsdividethe HBFACvalueintothevolumeofwaterrequiredper acre.AnETovalueof3260gal/acwouldrequire wateramountsof[(3260)/(72.6)=]45gallonsper100 ft.Adriptubewithadeliveryrateof0.5gpm/100ft wouldtake90minutestoapply45gallonsper100ft (@100%efficiency).Similarly,ifacitrusgrovehas 120treesperacre,awaterrequirementof3260 gallonsperacreisequivalentto[(3260)/(120)=]27 gallonspertree.Therefore,ifeachtreehada15gph sprayjet,1.8hoursofruntimewouldberequiredto applythe27gallons(@100%efficiency). Cropcoefficientsandirrigationsystemefficiency shouldbeconsideredwhendeterminingthetotal irrigationrequirementforthecrop.Eachofthe aboveexampleswerebasedon100%application efficiency,thusadditionaltimeandwaterwillneedto bescheduledfortheactualconditionsinindividual 1.ThisdocumentisFactSheetAE-251,aseriesoftheAgriculturalEngineering,aseriesoftheAgriculturalEngineeringDepartment,Florida CooperativeExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida.FirstPublishedMarch1993.DripTipNo. 9304.Publicationdate:July1994. 2.G.A.Clark,AssociateProfessor,AgriculturalEngineeringDepartment,ExtensionIrrigationSpecialist;C.D.Stanley,AssociateProfessor,Soil andWaterScience,GulfCoastResearchandEducationCenter,Bradenton,FL;CooperativeExtensionService,InstituteofFoodand AgriculturalSciences,UniversityofFlorida,GainesvilleFL32611. TheInstituteofFoodandAgriculturalSciencesisanequalopportunity/affirmativeactionemployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,age,handicap,ornational origin.Forinformationonobtainingotherextensionpublications,contactyourcountyCooperativeExtensionServiceoffice. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/JohnT.Woeste,Dean

PAGE 2

UsingReferenceEvapotranspirationData Page2fields.Finally,irrigationruntimewilldependon othersystemrequirementssuchasminimumruntime tofillpipes,chemigationneeds,oropportunitytime forwatertomovefromtheemittersintothecrops rootzone. SummaryofConversions *1Acre-inch=27154gals/ac *1Acre=43560ft2*LBFAC=43560/bedspacing *HBFAC=LBFAC/100 *Waterrequiredper100bedfeet =[gals/ac]/[HBFAC] *Waterrequiredpertree =[gals/ac]/[#treesperacre] Table1. EstimatedaveragedailyreferenceETdataforFlorida1. MONTH NORTHFLORIDA CENTRALFLORIDA SOUTHFLORIDA (inches) (gal/ac/day) (inches/day) (gal/ac/day) (inches/day) (gal/ac/day) JAN 0.06 1630 0.09 2440 0.10 2720 FEB 0.09 2440 0.12 3260 0.13 3530 MAR 0.12 3260 0.15 4070 0.16 4340 APR 0.16 4340 0.19 5160 0.19 5160 MAY 0.19 5160 0.20 5430 0.19 5160 JUN 0.19 5160 0.20 5430 0.18 4890 JUL 0.18 4890 0.19 5160 0.18 4890 AUG 0.17 4620 0.17 4620 0.17 4620 SEP 0.15 4070 0.16 4340 0.15 4070 OCT 0.12 3260 0.14 3800 0.14 3800 NOV 0.08 2170 0.11 2990 0.12 3260 DEC 0.06 1630 0.08 2170 0.10 2720 1DatasourceincludesUniversityofFlorida,CooperativeExtensionServiceBulletin205"PotentialEvapotranspiration ProbabilitiesandDistributionsinFlorida".