Measurements of rubber tree transpiration in adult plantations
In order to assess water balance of rubber plantations at plot scale, accurate dynamic measurements of tree transpiration is required. Sapflow was measured in a 12 years old plantation (RRIM 600) in eastern Thailand, by heat dissipation method (Granier 1985, 1987) using home-made 20 mm-long radial probes, continuously heated (0.2 W), and connected to a data logger. The calibration of the homemade probes was checked in the laboratory with reference to the gravimetric method. We adjusted the experimental devices to rubber field conditions and evaluated the different sources of variability to design the appropriate monitoring process. Natural thermal gradient was not significant. Vertical variation along the trunk below canopy was low. Conversely a significant azimuthal variation was recorded, though without specific trend. Accordingly 2 probes (one on the North face, one on the South face), located above the tapping panel were used for monitoring. Radial distribution of sapflow was recorded, using a long probe, and our results showed significant variations of sapflow along the radius. A function was derived from these radial variations to estimate total tree sapflow from measurements within the outer 2 cm of sapwood. Finally to evaluate stand transpiration (mm h-1), trees were sampled according to trunk diameter. Such data will be used to partition evapotranspiration measured on the same plot by eddy-correlation between tree transpiration, T, and soil and understorey evaporation, E. (Texte intégral)
| Main Authors: | , , , , , , |
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| Format: | conference_item biblioteca |
| Language: | eng |
| Published: |
Rubber Research Institute of Vietnam
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| Subjects: | F62 - Physiologie végétale - Croissance et développement, Hevea brasiliensis, plantations, transpiration, http://aims.fao.org/aos/agrovoc/c_3589, http://aims.fao.org/aos/agrovoc/c_5990, http://aims.fao.org/aos/agrovoc/c_7871, http://aims.fao.org/aos/agrovoc/c_7701, |
| Online Access: | http://agritrop.cirad.fr/552382/ http://agritrop.cirad.fr/552382/1/ID552382.pdf |
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| Summary: | In order to assess water balance of rubber plantations at plot scale, accurate dynamic measurements of tree transpiration is required. Sapflow was measured in a 12 years old plantation (RRIM 600) in eastern Thailand, by heat dissipation method (Granier 1985, 1987) using home-made 20 mm-long radial probes, continuously heated (0.2 W), and connected to a data logger. The calibration of the homemade probes was checked in the laboratory with reference to the gravimetric method. We adjusted the experimental devices to rubber field conditions and evaluated the different sources of variability to design the appropriate monitoring process. Natural thermal gradient was not significant. Vertical variation along the trunk below canopy was low. Conversely a significant azimuthal variation was recorded, though without specific trend. Accordingly 2 probes (one on the North face, one on the South face), located above the tapping panel were used for monitoring. Radial distribution of sapflow was recorded, using a long probe, and our results showed significant variations of sapflow along the radius. A function was derived from these radial variations to estimate total tree sapflow from measurements within the outer 2 cm of sapwood. Finally to evaluate stand transpiration (mm h-1), trees were sampled according to trunk diameter. Such data will be used to partition evapotranspiration measured on the same plot by eddy-correlation between tree transpiration, T, and soil and understorey evaporation, E. (Texte intégral) |
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