Use of the heat dissipation technique for estimating the transpiration of olive trees Abid Karray J. 1,2 , Masmoudi M. M

1. 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 1Institut National Agronomique de Tunisie 2Institut de Recherche pour le Développement, U-Montpellier. Amman 30 Sept-5 October, 2005

2. 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.

3. SUBJECT MATTER • Determination of water consumption in intercropping system (olive–potato crop) • olive transpiration (T): Sap flow method • potato evapotranspiration (ETc): water balance

5. 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

7. 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.

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

9. 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.

10. 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.

12. 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.

13. 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)

14. 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.

17. 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.

18. 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.

19. 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.

20. THANKS FOR YOUR ATTENTION