Approach to assess infrared thermal imaging of almond trees under water-stress conditions

12 Pages·2003·1.87 MB·English

Original article
Approach to assess infrared thermal imaging
of almond trees under water-stress conditions
IvánGARCÍA-TEJERO,VíctorHugoDURÁN-ZUAZO,JavierARRIAGA,AlmudenaHERNÁNDEZ,LuisaMariaVÉLEZ,
JoséLuisMURIEL-FERNÁNDEZ
Inst.Andal.Investig.Form. Approach to assess infrared thermal imaging of almond trees under water-stress
Agrar.Pesq.Prod.Ecol. conditions.
(IFAPA),Cent.“LasTorres-
Abstract – Introduction. Optimising agricultural water use implies the combination of physiological,
Tomejil”,Ctra.Sevilla-Cazalla, technologicalandengineeringtechniques,especiallythoseforcontinuouslymonitoringthewaterstatus
Km.12,2,AlcaládelRío of plants subjected to deficit irrigation. A methodology to estimate water stress of young almond trees
(Sevilla),Spain,victorh.duran@ fromthermalimageswasdevelopedbasedonassessingthephysiologicalstatusofalmondcropsunder
juntadeandalucia.es limitedwater-supplyconditions.Materialsandmethods.Twoirrigationtreatmentsweretestedduring
themaximumevapotranspirativedemandperiod(214thtothe243rddayoftheyear)inanexperimental
almond [Prunus dulcis (Mill) D.A. Webb, cv. Guara] orchard: a low-frequency deficit irrigation (LFDI)
treatment, irrigated according to the plant-water status, and a fully irrigated treatment (C ) at 100% of
100
crop evapotranspiration. Daily canopy temperature at midday (T ) was measured with an infrared
C
camera,togetherwithstandardmeasurementsofstem-waterpotential(Ψ )andstomatalconductance
Stem
(g ). The time course of these parameters and their relationships were analysed. Resultsanddiscus-
S
sion.Thetimecourseoftheparametersstudiedshowedhighlysignificantcorrelationsamongthediffe-
rentialsofcanopy-airtemperature(ΔT),Ψ andg .Themethodologicalprotocolforanalysingthermal
Stem S
imagesallowedatimesavinginprocessinginformationandadditionallyofferedthepossibilityofestima-
ting the Ψ and g values. Conclusion.Our results confirm that infrared thermography is a suitable
Stem S
technique for assessing the crop-water status and can be used as an important step towards automated
plant-waterstressmanagementinalmondorchards.
Spain / Prunus dulcis / canopy / temperature / infrared thermography / water
requirements/soilwaterdeficit
Approchepourévaluerl’imageriethermiqueinfrarouged’amandiersenconditionsde
stresshydrique.
Résumé–Introduction.Optimiser l’utilisation de l’eau en agriculture implique de combiner des tech-
niques physiologiques, technologiques et d’ingénierie, en particulier celles qui permettent de surveiller
enpermanencel’étathydriquedeplantessoumisesàundéficitd’irrigation.Uneméthodologiepouresti-
merlestresshydriquedejeunesamandiersàpartird’imagesthermiquesaétédéveloppéesurlabasede
l’évaluationdel’étatphysiologiqued’arbresplacésenconditionsd’alimentationeneaulimitée.Matériel
etméthodes.Deuxtraitementsd’irrigationontététestésaucoursdelapériodededemandeevapotrans-
pirativemaximale(214eau243ejourdel’année)dansundispositifexpérimentalenvergerd’amandiers
[Prunusdulcis (Mill.) D.A. Webb., cv. Guara]: un traitement avec une irrigation déficitaire à basse fré-
*Correspondenceandreprints quence(LFDI),irriguéenfonctiondustatuthydriquedesplants,etuntraitementirriguéà100%del’éva-
potranspirationdescultures(C ).Latempératurequotidienneducouvertàmidi(T )aétémesuréeà
100 C
l’aided’unecamérainfrarouge,ainsiquedesmesuresstandardsdupotentielhydriquedelatige(Ψ )
Stem
etdelaconductancestomatique(g).L’évolutiondansletempsdecesparamètresetleursrelationsont
s
Received13December2011 étéanalysées.Résultatsetdiscussion.L’évolutiondansletempsdesparamètresmesurésetleursrela-
tions ont mis en évidence des corrélations hautement significatives entre la différence de température
Accepted9February2012
canopie-air(ΔT),etlesparamètresΨStem,etg .Leprotocoleméthodologiquepourl’analysedesimages
S
thermiquesapermisungaindetempspourletraitementdel’informationetaoffertenpluslapossibilité
Fruits,2012,vol.67,p.463–474 d’estimer les valeurs de ΨStem et de gS. Conclusion. Nos résultats confirment que la thermographie
infrarougeestunetechniqueappropriéepourl’évaluationdel’étathydriquedesculturesetqu’ellepeut
©2012Cirad/EDPSciences
êtreutiliséecommeunetechniqueadaptéeàlagestionautomatiséedustresshydriquedesplantsenver-
Allrightsreserved
gersd’amandiers.
DOI:10.1051/fruits/2012040
www.fruits-journal.org
Espagne / Prunus dulcis / couvert / température / thermographie infrarouge /
RESUMENESPAÑOL,p.474 besoineneau/déficithydriquedusol
ArticlepublishedbyEDPSciences
Fruits,vol.67(6) 463
I.García-Tejeroetal.
1. Introduction toT ,whichislinkedwithlowercropeva-
air
potranspiration and stomatal conductance
[15, 16].
Almond [Prunus dulcis (Mill) D.A. Webb],
withmorethan650,000ha,isaftertheolive Newapproachesforassessingtheplant-
(OleaeuropaeaL.)andthegrape(Vitisvini- waterstatusthroughremoteornon-invasive
fera L.) the third woody crop in growing methodshavebeenproposedusinginfrared
area in Spain1. Although traditionally con- thermometry. Canopy temperature has
sidered a highly drought-tolerant crop, been shown to be associated with other
under non-limiting conditions, almond sig- physiological parameters such as stomatal
nificantly improves crop yield, generating conductance, Ψ or maximum daily
Stem
high economic profits, with yields up to shrinkage, among others [17–19]. These
10 times higher than under rainfed condi- measurements are taken mainly through
tions [1–4], and with a great adaptability to infrared cameras, which capture thermal
watershortage[5,6].Inmanyaridandsemi- imagesofcrops,inasimilarwaytosatellite
aridareas,irrigationavailabilityisoneofthe imagery, but with the advantage that these
most limiting factors for increasing almond can be taken at any time, without the limi-
yield,andthereforedeficitirrigationisoften tations to the treatment and analysis of
aviablealternativetomaintaincropyieldat images remotely captured by satellite [20].
levelssimilartothoseofnon-limitingwater
Despite the advantages associated with
conditions, and hence, improving over
theuseofsuchtools,somelimitationsresult
rainfed situations [7, 8].
from the procedure of capturing and
However,underdeficitirrigation,acon-
processingdata,requiringinmanycasesthe
tinuouscontroloftree-waterstatusiscrucial
useofcomplexsoftwareandthusreducing
[9]. The stem-water potential (Ψ ) and
Stem the operational ease and affordability of
stomatal conductance (g ) provide refer-
S such techniques. Hand-operated cameras
encemeasurementsforassessingtheplant-
offerimagesofindividualplantsorportions
waterstatus,andhencehavebeenusedfor
thereof,butwiththedisadvantagethat,dur-
irrigationschedulinginmanycrops[10–12].
ing the photographing process, different
According to García-Tejero et al., such
elements(soil,shadyareas,skyorportions
measurements require time and adequate
ofadjacentplants)canbereflected,requir-
fieldstaff[13].Thus,thedirectexamination
ing subsequent time-consuming image
of some plant physiological factors is nec-
processing. This difficulty is especially
essary to optimise irrigation, especially in
markedinyoungwoodycrops,withdiscon-
arid and semi-arid areas such as SW Spain,
tinuous canopies [14].
where irrigation is crucial for enhancing
crop production. Many authors have described different
methods to overcome such limitations,
Therefore, alternative indicators related
although all approaches require different
tothecrop-waterstatusareessentialforirri-
image processing, either through editing
gationtimingandautomation.Canopytem-
software or pixel classification, or through
perature (T ) indicates crop-water stress,
C relatively laborious statistical analysis [21–
this being highly related to the daily crop
24].
transpiration. In crop transpiration, latent
heatisgivenoffasevaporation,decreasing The aim of our study was to develop an
thecanopytemperature(T )withrespectto alternative methodology for assessing the
C
airtemperature(T )[14].Whenthecropis canopy temperature (T ) from thermogra-
air C
subjected to water stress the transpiration phyimageswithoutpretreatingimages,and
leveldeclines,increasingtheT withregard avoidinginterferenceandmaskingbyother
C
materials. This is accomplished with stand-
1FAOSTAT,Foodandagricultureorganizationof ard physiological parameters for assessing
theUnitedNations,availableathttp://faostat. water stress in almond trees under water-
fao.org/[September2011]. stress conditions.
464 Fruits,vol.67(6)
Thermalimagingofalmondtrees
2. Materials and methods Regarding the low-frequency deficit irri-
gation(LFDI)treatment,itwassubjectedto
irrigation restrictions during the maximum
2.1. Experimental conditions
evapotranspirativedemandperiod,fromthe
214th to the 243rd day of the year (DOY).
Thetrialwasconductedduring2011,inan
Thatis,thistreatmentreceivednoirrigation
experimental orchard of almond [Prunus
in relation to the control treatment, which
dulcis (Mill.) D.A. Webb., cv. ‘Guara’,
was fully irrigated, according to the crop
grafted onto GF677], located in Alcalá del
evapotranspiration demand (ETc), using a
Río, some 18 km to the north of Seville
referencecropcoefficient(Kc)andareduc-
(37°30’N,5°58’W)(SWSpain).Theyoung
tion coefficient (Kr) of 0.6 and 0.3, respec-
almond orchard was planted in 2010,
tively [27]. Irrigation treatments were
spacedat7 m× 6 m,anddrip-irrigatedwith
displayed in a randomised-block design
apipelinewithtwopressure-compensated
emitterspertree,withaflowrateof2 L·h–1. withthreereplicateplotspertreatment,and
monitoring six trees per replicate.
Thesoilissiltyloam,typicalFluvisol[25],
with 2.5 m depth, fertile, and low organic-
matter content (< 15.0 g·kg–1). Tree roots 2.3. Plant measurements
were located predominantly in the upper-
most0.45 moftheprofile,correspondingto During the experimental period (214th
theintendedwettingdepth.Soil-water-con- to 243rddayoftheyear),canopytempera-
tentvaluesatfieldcapacity(–0.3 MPa)and ture readings were taken with a thermal-
wiltingpoint(–1.5 MPa)were0.39and0.13, imaging thermographic camera (Therma-
respectively, with an available soil-water CamTMFLIR-SC660System,Inc.,UK).This
capacity averaging 0.26 m3 ·m–3. camerasuppliesinfraredorvisiblespectrum
images of high quality, allowing accurate
Theclimateintheareaisattenuatedmeso-
temperaturemeasurement,withaninfrared
Mediterranean [26], with an annual average
pixelresolutionof640× 480andaspectral
precipitation and reference evapotranspira- rangeof7.5 µmto13.5 µm2,withanestab-
tion of (534 and 1,400) mm·year–1, respec-
lishedemissivityforcropvegetationof0.98
tively.
[28]. With the same periodicity, Ψ was
Stem
measured in two leaves per sampling tree,
2.2. Experimental set-up and between 11:00 and 12:00 h solar time, and
every24–48hours.Ψ wasmonitoredin
irrigation treatments Stem
shaded mature leaves close to the north
quadrantandnearthetrunk,usingaScholan-
Two irrigation treatments were applied
der pressure chamber [29] (Soil Moisture
under both experimental conditions: (a)
Equipment Corporation, Sta. Barbara, CA,
controltreatment(C ),irrigatedat100%of
100 USA). At the same time, the stomatal con-
cropevapotranspiration(ET ),and(b)low-
C ductance g was measured in two sunny
frequencydeficitirrigation(LFDI),irrigated S
leavespertree,usingadiffusionporometer
according to the plant-water status. So, in
AP-4(Delta-TDevices,Cambridge,UK).
thistreatment,differentirrigation-restriction
cycles were established according to the
canopy temperature (T ) at midday. When 2.4. Infrared image acquisition,
C
significant differences (p < 0.05) were analysis, and calculations
detected between control (C ) and LFDI,
100
stressed trees were irrigated with the same Theimagesweretaken3 mfromthesunny
amount of water and frequency as C100. sideofthecanopy,withawetcooledcloth
Additionally, when T values at midday in
C
thistreatmentweresimilar toTCvaluesfor 2FlirSystemsThermography,FlirP-Series,infrared
the control treatment, irrigation was with- perfection,availableatwww.support.flir.com/../
held until the T values were again signifi- A365-P%20series%20brochure%20def.pdf/
C
cantly different. [September2011].
Fruits,vol.67(6) 465
I.García-Tejeroetal.
way to solve this difficulty is to select and
exportdifferentimagesections;inourcase,
three consecutive areas per image were
required.
Theflowchartforimageanalysisprocess
from selected images was synthesised (fig-
ure1).Thus,sinceeverysectionwassaved
indifferentdatasheetfiles,itwasnecessary
to make a selection by removing for each
‘CSV’ file the temperature values below a
certain threshold (temperature values per-
tain to wet cooled cloth), and thus leaving
thepixelsfromthetreecanopywithitstem-
peraturevalues.Determiningthemeanand
variance for every file is quite easy, but, in
ordertodeterminetherealmean(andespe-
cially the variance) of the full image, more
complex procedures are required.
Toautomatethisprocedure,aCprogram
[30,31]wascreated.Thisprogramasksthe
operatorforthedesiredfilenamesandtem-
perature limit, erasing the data below the
limit,andsavestheresultsinplaintextfor-
mat, calculating the average (T , ºC) and
C
varianceforthefullsetoffiles.Finally,itcre-
ates a DIB (Device-Independent Bitmap)3
monochrome file to show the ‘real image’
of the tree canopy. The bitmap (BMP) file
waschosenbecauseitcanbeeasilyimple-
mented without specific software libraries.
The program runs with up to three image
sectionsandithasbeenprogrammedusing
cross-platform standards; therefore, it can
beusedinanysystemwithaconsoleinter-
face. Additionally, the minimum (T , ºC)
min
andmaximum(T ,ºC)temperaturescan
max
bedeterminedforeachcanopymonitored,
Figure1.
(screen) just behind the tree canopy, in
using the same program.
Flowchartforimageanalysis
ordertosimplifytheisolationofthecanopy
process.
surfacethroughimageprocessingbasedon
temperature differences. The raw thermal
2.5. Data analysis
imageswereobtainedbymeansofTherma-
CamExplorersoftware(FLIRQuickReport)
as a ‘TIFF’ image. The images were then Anexploratoryanddescriptiveanalysiswas
processed, using the FLIR software for done of Ψ , stomatal conductance and
Stem
exportingtheseimagesfromTIFFtoa‘CSV’ canopy temperature, followed by t-test
file(comma-separatedvalues).Thenewfile analysis using the SPSS 15.0 statistical
generatedcontainedalargenumberofcells, package (SPSS, Chicago, IL, USA). Addi-
with temperature values in each tile per tionally, Ψ , stomatal conductance and
Stem
pixel.TheCSVfilecouldbeuploadedwith
an ‘XLS’ datasheet, which was limited to a 3MSDN,DIBsandtheiruses,availableathttp://
maximum of 256 columns, and, in most msdn.microsoft.com/en-us/library/ms969901.
cases, images were considerably larger. A aspx[September2011].
466 Fruits,vol.67(6)
Thermalimagingofalmondtrees
Figure2.
Thermalimageprocessingof
almondtreessubmittedtotwo
treatments:fullyirrigated
treatmentandlow-frequency
deficitirrigationtreatment
duringthemaximum
evapotranspirativedemand
period.
temperaturevariation(ΔT)werecorrelated, belonged to other tree sections as well as
estimatingthefeasibilityofcanopytemper- other materials present in the field.
ature readings as a continuous plant-based
The result was a CSV file, after the con-
water-stress indicator, and establishing the
versiondata,whichindicatedthecellswith
physiological threshold values. Finally, a
temperaturevaluesoutsideofthesetrange,
validation was conducted to assess the
keeping the values that corresponded
performanceoftheserelationships,estimat-
strictly to the tree canopy studied. After-
ing the determination coefficient (r2) and
wards,theCprogramcreatedaBMPfile,in
root mean square error (RMSE).
whicheachcellwithacanopy-temperature
value was converted into a ‘black pixel’,
with ‘white’ representing the pixels corre-
sponding to the cells that had been
3. Results and discussion
screened. The code box for the Basic pro-
gramming language that describes its pro-
3.1. Processing images cedure is given (figure3).
Themainadvantageofthisprotocolisthe
In each thermal image the threshold was time saved in processing thermal images.
determinedforthemaximumandminimum TheCprogramallowedmaximumandmin-
temperaturesthatallowedthepre-treatment imum threshold temperature values to be
of data (figure2). A post-treatment con- defined by selecting only the pixels that
sistedofobtainingforeachimageonlythe belongedtothecanopyarea,avoidingeven
pixels that belonged solely to the canopy those corresponding to values of the trunk
area, avoiding the masking pixels that or branches.
Fruits,vol.67(6) 467
I.García-Tejeroetal.
Figure3.
Codeboxinprogramming
languageforconversionof
dataregardingparameters
measuredonalmondtrees.
3.2. Plant physiological dynamics a total of 27.7 mm of water, this being
approximately 90% of ETc, whereas LFDI
received no irrigation. These irrigation
ThetimecourseofΨ ,stomatalconduct-
Stem dynamics in each treatment promoted sig-
anceg andcanopytemperatureT forthe
s C nificanteffectsonthephysiologicalvariables.
control and LFDI treatment was registered
fromthe214thtothe243rddayoftheyear The ΨStem in control trees ranged
(tableI). During the experimental period, between –0.91 MPa and –1.75 MPa, these
accumulativeETcwascloseto31 mm.That valuesbeinginlinewiththosereportedby
is,duringthisperiod,controltreesreceived other authors under non-limiting water
468 Fruits,vol.67(6)
Thermalimagingofalmondtrees
TableI.
Timingevolutionofstem-waterpotential(Ψ ),stomatalconductance(g )andcanopytemperature(T )for
stem S C
almondtreesduringamonitoringperiod.
Dayofthe Air Controltreatmentfullyirrigatedat100% Low–frequencydeficitirrigation
year temperature (C (LFDI)
100)
(ºC) Stem-water Stomatal Canopy Stem-water Stomatal Canopy
potential conductance temperature potential conductance temperature
Ψ g T Ψ g T
stem S C stem S C
(MPa) (mmol·m–2·s–1) (ºC) (MPa) (mmol·m–2·s–1) (ºC)
214 27.2 –1.4±0.1 95.1±18.8 26.6±0.7 –1.1±0.2 108.4±27.5 27.2±0.4
216 33.0 –1.4±0.1 356.0±35.6 29.6±0.4 –1.9±0.2* 423.0±58.4 29.2±0.9
217 32.6 –1.3±0.1 290.0±68.3 30.3±0.5 –1.7±0.2* 253.2±32.9 30.9±0.5
220 35.0 –1.3±0.2 394.2±57.6 30.9±0.5 –1.7±0.1* 274.4±65.6 31.0±0.5
222 33.6 –1.7±0.2 336.9±76.8 31.8±0.3 –2.1±0.1* 262.5±39.5 32.0±0.4
224 30.8 –1.2±0.2 540.8±43.2 29.4±0.4 –1.7±0.2* 326.0±63.3* 29.3±0.2
228 34.0 –1.5±0.1 482.8±66.3 32.4±0.4 –1.8±0.3* 348.2±95.7 32.4±0.7
230 30.6 –1.5±0.2 494.7±85.5 29.6±0.5 –1.9±0.3* 387.8±97.0 29.5±0.5
234 27.8 –0.9±0.1 523.3±43.7 27.1±0.4 –1.5±0.2* 404.5±75.9* 27.8±0.3*
237 30.4 –1.3±0.3 383.8±53.5 28.5±0.4 –1.9±0.2* 272.0±82.6* 28.6±0.6
243 25.7 –1.3±0.1 358.3±29.6 27.1±0.9 –1.7±0.2* 228.5±43.5* 27.8±0.9*
±:Standarddeviation.
*Significantdifferencesbetweentreatmentsforasingleday,accordingtoStudent’st-test(t-statisticandp<0.05).
availability [32–34], whereas LFDI ranged The Ψ and stomatal conductance
Stem
between –1.18 MPa and –2.18 MPa. Thus, records in LFDI were according to those
throughout the monitoring period, signifi- reported by other authors such as Gomes-
cant differences between treatments were Laranjoetal.,whoestablishedΨ ranges
Stem
found. of –2.3 MPa to –2.9 MPa in non-irrigated
almonds[35].AsstatedbyChavesetal.,sto-
Accordingtothetimecourseofstomatal
matal aperture is governed by several
conductance,thesedifferenceswerenotas
pronounced as in the Ψ , ranging from weather and soil-water conditions [36].
Stem
(95 to 540) mmol·m–2·s–1 in control trees
Accordingtothesensitivityofthediffer-
andfrom(108to423) mmol·m–2·s–1inLFDI,
entwater-stressindicators,thisisrelatedto
these values being in line with those
thedegreeofchangeinwaterstatusthatcan
reportedbyNortes[34]inalong-termexper-
be found statistically. Therefore, the sensi-
iment of regulated deficit irrigation in
tivityofawater-stressindicatorisexpected
almond trees. The limited effect of water
toincreasewiththelevelofresponseofthe
deficitinthisparameterwasreflectedinthe
sensor to changes in water status, and to
absence of significant differences between
decrease with greater variability between
treatmentsformostofthesamplingperiod,
sensors/readings [37]. In line with these
which were patent only in the final days
results, water stress was detected earlier
(DOY: 234–243).
withΨ thanwithstomatalconductance
Stem
Due to the strong relationship between andcanopytemperature.Inaddition,other
T and crop-transpiration levels, the T authorssuchasGarcía-Tejeroetal.reported
C C
showedasimilartrendofstomatalconduct- thehighersensitivityofthecanopytemper-
ance,hencethesignificantdifferencesbeing ature for detecting water stress in citrus
shownattheendofthemonitoringperiod. trees,incomparisonwithotherphysiological
Fruits,vol.67(6) 469
I.García-Tejeroetal.
Figure4. increased up to air temperature, reflecting
Relationshipbetween that, below this value there is a significant
temperaturevariation(ΔT)and decrease in the canopy cooling capacity
stem-waterpotential(ΨStem) throughitstranspiration;decreasingthissig-
foralmondtrees. nificantly.Significantrelationshipsbetween
ΔT and stomatal conductance were also
found (figure5, r2 = 0.26), although there
was greater variability in comparison with
Ψ . In this context, Jones et al. argued
stem
that the difficulty of relating the average
temperatureofmultipledifferentlyoriented
surfacestostomatalconductanceofindivid-
ualleaveswouldbehighlyrelatedtotherel-
ativeorientationofleaveswithrespecttothe
solarradiation[39].Thedevelopmentstages
ofthecanopystructureandtheleavesalso
affectthetemperatureandhowitvarieswith
view angle. In consideration of these rela-
tionships, stomatal conductance values
below 335 mmol·m–2·s–1 would promote
Figure5. increments in the differential of canopy-air
Relationshipbetween temperature (ΔT) of up to 0 °C (figure5).
temperaturevariation(ΔT)and Thatis,belowthisvaluethecroptranspira-
stomatalconductance(g )for
S tion was being limited by a water shortage
almondtrees.
or worse weather conditions, and the can-
opy cooling capacity would be limited.
Thus, decreased water uptake closes sto-
mata,loweringtranspirationandraisingleaf
temperatures [15, 16, 40].
Despite this, it is evident that other vari-
ablessuchasVPD(VaporPressureDeficit),
R (net radiation) or the timing measure-
n
mentshouldbetakenintoaccountwhenan
irrigation scheduling is developed, taking
theΔTaspriorityinformation.Accordingto
Sepulcre-Cantó et al., similar relationships
between Ψ and T for olive trees were
Stem C
reported,withr2varyingbetween0.25and
0.62 [41], suggesting that ΔT is a potential
variablessuchasΨ orstomatalconduct- parameter for detecting water stress at the
Stem
ance [38]. tree level. In addition, Wang and Gartung
[23] pointed out the strong relationships
(r2 = 0.70)betweenΔTandΨ inpeach
3.3. Relating thermal canopy Stem
[Prunus persica (L.) Batsch] trees. Also,
temperature to other physiological
García-Tejero et al. showed in citrus trees
parameters and model validation highly significant relationships of ΔT vs.
Ψ (r2= 0.75)andstomatalconductance
Stem
Asameansofestablishingthepatternofcrop (r2= 0.46)[39].Consequently,theseauthors
physiological response to water stress, the suggested the use of infrared canopy-tem-
relationships among the parameters meas- perature measurements as a promising
uredwerestudied.Significantrelationships method for assessing plant-water stress,
(p < 0.01) were found for ΔT and Ψ especially in arid and semiarid climates
Stem
readings (figure4, r2= 0.35). It was found underdeficit-irrigationstrategiesontheplot
that, for Ψ below –1.8 MPa, the T scale. However, it must be taken into
Stem C
470 Fruits,vol.67(6)
Thermalimagingofalmondtrees
account that these relationships would be Figure6.
anapproximationtothetruevaluesofΨ Relationshipbetweenthe
Stem
and stomatal conductance, and, hence, estimatedandthemeasured
stem-waterpotential(Ψ )
thesewouldbeapreliminaryassessmentof Stem
foralmondtrees.The
crop water stress.
continuouslinerepresentsthe
Given these relationships, the software linearrelationbetween
used could be modified. That is, this was estimatedandmeasured
abletoprovidenotonlytheaveragevalues Ψ ,whereasthedashedline
Stem
of the T and hence the ΔT, but also an showsa1:1relationbetween
C
approach to Ψ and stomatal conduct- thesevariables.
Stem
ance. This improves other known software
thatonlyallowstime-consumingprocessing
of thermal images and moreover does not
indicate the crop-water status based on
other physiological variables.
Thus,theprogramwasmodifiedinorder
to estimate the stomatal conductance and
Ψ bytakingintoaccounttheT .Anew
Stem C
query line was introduced to ask the user
which values could be obtained for the air Figure7.
Relationshipbetweenthe
temperature(T ).Withtheexpectedvalues
(E) and the vaariirance (σ2) for the tempera- estimatedandthemeasured
stomatalconductance(g )for
ture, the expected values and variance for s
almondtrees.Thecontinuous
stomatalconductanceandΨ canbecal-
Stem linerepresentsthelinear
culated as follows: relationbetweenestimatedand
measuredΨ ,whereasthe
Stem
dashedlineshowsa1:1
relationbetweenthese
variables.
fieldforΨ showsthattheestimatesare
Stem
closetothe1:1line,withaslopeof0.67(fig-
ure6).However,whenfieldvaluesofΨ
Stem
werebelow1.6 MPa,theestimateprovedto
whereErepresentstheexpectedvalues;T , beaslightoverestimationofthisparameter.
C
the canopy temperature; T , the air tem- In relation to the estimation of stomatal
air
perature; µ, the average; g , the stomatal conductance, this was slightly worse than
s
conductance;Ψ ,thestem-waterpoten- Ψ (figure7), values being underesti-
Stem Stem
tial at midday; and σ2, the variance. matedfortheentirerangeofmeasurements.
The approach was assessed considering Similar findings have been reported by
the relationships from values measured for Jones etal. [21], Smith [42], and Testi etal.
Ψ andstomatalconductancevs.theval- [43],amongothers,withespeciallyremark-
Stem
uesestimatedfromΔT.Thevalidationofthe ablerelationshipsbeingcalculatedbyBerni
estimated values vs. those measured in the etal.inolivetreesformappingthecanopy
Fruits,vol.67(6) 471
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conductance on the plot scale using high- (Eds.), Almond orchard management, Div.
resolution thermal-sensing imagery [20]. Agric.Sci.,Univ.Calif.,Berkeley,U.S.A.,1978,
These authors reported highly significant pp.46–51.
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mated stomatal conductance, with slopes icitirrigationduringthekernelfilling.Period
ranging between 4.50 and 1.07, depending andoptimalirrigationratesinalmond,Agric.
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[3] Goldhamer D.A., Viveros M., Salinas M.,
Assuming these results, canopy temper-
Regulated deficit irrigation in almonds:
ature would be a profitable water stress
effects of variations in applied water and
index, especially for monitoring of large
stresstimingonyieldandyieldcomponents,
crop areas. The proposed method allows
Irrig.Sci.24(2006)101–114.
onetoprocessthecropphysiologicalstatus
[4] NanosG.D.,KazantzisI.,KefalasP.,Petrakis
inrelationtoitswaterstatusquickly.How-
C.,StravroulakisG.G.,Irrigationandharvest
ever,althoughfurtherworkmaybeneeded
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position,Sci.Hortic.96(2002)246–256.
measurementswhenweatherconditionsare
[5] CastelJ.R.,FereresE.,Responsesofyoung
highly variable, the proposed technique
almondtreestotwodroughtperiodsinthe
constitutes a potential tool for precision
field,J.Hortic.Sci.57(1982)175–187.
drought-stress and irrigation scheduling.
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4. Conclusions hazelnut trees during a deficit irrigation
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Our work presents a methodological pro-
posal for thermal-image analysis under [7] RomeroO.,BotiaP.,GarciaF.,Effectsofreg-
water-stress conditions, which has been ulateddeficitirrigationundersubsurfacedrip
irrigationconditionsonvegetativedevelop-
previouslydevelopedandevaluatedinjuve-
mentandyieldofmaturealmondtrees,Plant
nile almond trees. The procedure devel-
Soil260(2004)169–181.
opedconstitutesapromisingalternativefor
examining the crop-water status by select- [8] Durán Z.V.H., Rodríguez C.R., Franco D.,
ingtherealareafromplantcanopyimages Impactofsustained–deficitirrigationontree
growth,mineralnutrition,fruityieldandqua-
andavoidingmaskingwithothermaterials.
lityofmangoinSpain,Fruits66(2011)257–
In addition, according to our present 268.
results,theinfraredmeasurementofcanopy
[9] Johnson R.S., Handley D.F., Using water
temperaturecanbeusedforestimatingthe
stresstocontrolvegetativegrowthandpro-
Ψstemandstomatalconductanceparameters ductivity of temperate fruit trees,
under water stress subjected to deficit-irri- HortScience35(2000)1048–1050.
gation programmes, by improving our
[10] Intrigliolo D.S., Castel J.R., Evaluation of
knowledge of plant-water relations.
grapevinewaterstatusfromtrunkdiameter
variations,Irrig.Sci.26(2007)49–59.
[11] García-Tejero I., Durán Z.V.H., Rodríguez
Acknowledgements
P.C.R.,MurielF.J.L.,Waterandsustainable
agriculture, Springer Briefs in Agriculture,
TheauthorI.García-Tejeroreceivedacon- Springer Science +Business Media, Neth.,
tract co-financed by the European Social 2011.
Fund Operational Programme (FSE) 2007-
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2013: "Andalucía is moving with Europe".
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