Heat-pulse measurements of sap flow in olives for automating irrigation: tests, root flow and diagnostics of water stress

The compensation heat-pulse method for measuring sap flow is tested here in olive trees ( Olea europaea L.). We describe a rigorous three-way examination of the robustness of the technique for this species, and examine the potential of the technique for an automatic control of the irrigation system....

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Bibliographic Details
Published in:Agricultural water management 2001-10, Vol.51 (2), p.99-123
Main Authors: Fernández, J.E, Palomo, M.J, Dı́az-Espejo, A, Clothier, B.E, Green, S.R, Girón, I.F, Moreno, F
Format: Article
Language:English
Subjects:
Agricultural and forest climatology and meteorology. Irrigation. Drainage
Agronomy. Soil science and plant productions
Biological and medical sciences
Embolisms
Fundamental and applied biological sciences. Psychology
General agronomy. Plant production
Heat pulse
Hydraulic behaviour
Irrigation. Drainage
Olive
Roots
Water stress
Xylem
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Summary:The compensation heat-pulse method for measuring sap flow is tested here in olive trees ( Olea europaea L.). We describe a rigorous three-way examination of the robustness of the technique for this species, and examine the potential of the technique for an automatic control of the irrigation system. Two tests were carried out using heat-pulse gear inserted into the stem of 12-year-old ‘Manzanilla’ olive trees. One test used forced-flow through a stem section, and the other involved measured water uptake by an excised tree. The measured sap flow in these two tests was in agreement with calculations from heat-pulse velocities when using a standard ‘wound correction’ to account for the presence of the probes and the disruption to the sap flow. Thus, this technique for monitoring transpiration can, we feel, be used with confidence in olives. The third experiment was carried out in the field, where we analysed sap flow data from two 29-year-old olive trees — one tree was under regular drip irrigation and the other was from dry-farming conditions. We use measurements of sap flow in the trunk to examine the hydraulic functioning of the tree, and to explore some diagnostics of water stress. Our heat-pulse measurements in the irrigated olive tree exhibited a profile of sap flow that was weighted towards the outer xylem of the tree trunk while the water-stressed trees in the field showed a profile of sap flow weighted towards the centre of the trunk. The loss of hydraulic functioning in the outermost section of the vascular system, as a result of water stress, we consider to be due both to stomatal control and to embolisms in the xylem vessels. The fourth experiment was also carried out in the field, in which sap flow measurements were made at three locations in the trunk as well as in two roots of another 29-year-old olive tree. The soil explored by each root, on opposite sides of the trunk, was differentially wetted by separate irrigation of each side. Our data showed that the surface roots were able to absorb water immediately after wetting, despite a reasonably prolonged period of moderate drought. Root activity quickly shifted to the regions where the soil had been wetted. A root in dry soil exhibited no flow at night, whereas sap flows of about 0.02 l h −1 were measured around midnight in the root drawing water from the wetter soil. Our observations suggest that the hydraulic behaviour of the trunk and surface roots might be used as a diagnostic of the onset,
ISSN:0378-3774
1873-2283
DOI:10.1016/S0378-3774(01)00119-6