2012 IAL Conference

A novel technique to measure the total evaporation and its components during

sprinkler irrigation

Jasim UddinRod Smith

Nigel HancockJoseph Foley

National Centre for Engineering In Agriculture (NCEA)University of Southern Queensland,

Toowoomba QLD 4350Australia

Presentation layout

Background Hypothesis Objectives Methodology Results Conclusions

BackgroundFigure 1: Components of evaporation losses during sprinkler

irrigation

Droplet evaporation

Canopy evaporationSoil evaporation

Background

Components Theoretical Experimental

Canopy evaporation

8% Unable to measure

Droplet evaporation

<1% 0-45%

Soil evaporation negligible Unable to measure

Limitations of the catch-can method

Laborious and time consuming Unable to measure ET over crop

(Source : Smith, Cotton CRC)

Catch-can

Limitations of the lysimeter method

Figure 3: Measured ET using lysimeter and predicted ET (source : Thompson et al. 1997)

Lysimeter could not measure ET during irrigation

Irrigation period

Background

Hypothesis:Eddy covariance – sap flow method can be used to measure total ET and its components during sprinkler irrigation

Objectives: To measure the total ET and transpiration

To estimate the components of ET

Methodology

Figure 4: Experimental set upEddy covariance system

Sap flow system

Methodology

Eddy covariance (ECV) system Sonic anemometer

Infrared Gas analyzer

Net radiometer

Sap flow system

Datalogger Hub

sensor Interface

MethodologyMeasurements

Latent heat flux (λE) and sensible heat flux (H)Eddy covariance technique

Net radiation (Rn) Four components net radiometer

Soil heat flux (G)Soil heat flux plates

Transpiration (T) measured bySap flow method

Air temperature (Ta) and Relative humidity (RH)

Temperature and RH probe

nE ET R H G

MethodologyData processing

Calculation of λE:

Bowen Ratio,

Calculations of ET in mm/hr :

Calculations of ETref : FAO Penman-Monteith

1nR G

E

/H E

(28.36 24)EET

Results Figure 3: Measurement of ET and tarnspiration

over mature cotton

Results Figure 4: Components of total ET measured by ECV-sap flow

method

ConclusionsMeasurement of total ET during sprinkler irrigation is possible which includes: canopy evaporation and droplet evaporation during

irrigation reduction of transpiration during irrigation canopy interception soil evaporation

Thanks for your attendance

Questions