Prsentation PowerPoint

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Use of the heat dissipation technique for
estimating the transpiration of olive
trees   Abid Karray J.1,2, Masmoudi M. M.1, Luc
J.P.2, Ben Mechlia N.1 1 Institut National
Agronomique de Tunisie 2 Institut de Recherche
pour le Développement, U-Montpellier. Amman 30
Sept-5 October, 2005
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CONTEXT

• This work has been conducted for a PhD
  thesis-University of Montpellier.
• The main framework is the developpment of
  practices that could improve WUE in arid Tunisia.
• It is linked to other research work on deficit
  irrigation and use of low quality waters.

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SUBJECT MATTER

• Determination of water consumption in
  intercropping system (olivepotato crop)
• olive transpiration (T) Sap flow method
• potato evapotranspiration (ETc) water balance

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• In Tunisia, intercropping system are gaining
  importance mostly in Central Tunisia.
• This system is adopted by farmers to
• increase water productivity
• - have spread production and income over the year

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• Estimation of transpiration is required for
  appropriate irrigation management and to increase
  water use efficiency at field level.
• In orchard, quantifiying water used by trees
  cannot be performed easily by water balance or
  micrometerological methods.
• Sap flow methods seem to have the potential of
  estimating transpiration course.

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• Sap flow methods
• - direct measurments
• - continuously records
• Differents techniques
• - Heat pulse
• - Heat balance
• - Heat dissipation

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EXPERIMENATAL LAYOUT

•  Central Tunisia, Chébika (Kairouan), semi-arid
  climate.
• 4 olive trees (Olea europea, cv Chemlali), age
  10 years old,
• 11x11 m.
• 3 probes per tree at 3 exposures North (N),
  South East (SE) and South West (SW).
• 2 data loggers (CR10X) for monitoring and
  recording probe signals on the 4 trees.

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HEAT DISSIPATION TECHNIQUE

• HDT  (Granier, 1985) is based on measurment of
  temperature difference between heated and
  unheated probes.
• Do and Rocheteau (2002) modified HDT to
  eliminate the influence of natural thermal
  gradient cyclic heating.

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• A sample of 95 days data was selected from
  01/07/03 to 31/12/03 period.
• Sap flow density is calculated according to Do
  and Rocheteau equation (2002) recalibrated on
  olive trees.

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Sap flow density (Fd) measured on 4 trees (T1 to
T4) on three directions North (N), South East
(SE) and South West (SW) on 31/08/03

• General consistency between haourly measurmetns
  pattern of the 12 probes
• But
• - High variability of absolute value of
  sap flow density ( maximum, cumulative)

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• The same variability between sensors was found
  within daily values
• Sap flow pattern seems to be related to probe
  position and local condition of conductivity in
  sapwood.

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CONCLUSIONS

• Hourly sap flow density show coherant pattern
  with climatic conditions but with large
  differences between probes on daily values scale.
• Behaviour of a single probe is consistent with
  the overall average for a wide range of
  transpiration rate.

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CONCLUSIONS

• Regression equation between sensors could be used
  to reconstitue missing values in case of
  technical problems or to reduce probe numbers in
  field when used for long term monitoring.
• Calibration for local range of transpiration is
  recommanded to use such models.
• HDT with cyclic heating is a sufficient way to
  provide transpiration pattern estimate on olive
  trees.

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CONCLUSIONS

• No apparent relationship between exposures of
  sensors and the flow distribution with the trunk
  cross section.
• 3 probes per tree seem to be adequate to produce
  good estimation of effective sap flow in sapwood
  area.

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THANKS FOR YOUR ATTENTION