ISHS Acta Horticulturae 618: XXVI International Horticultural Congress: Environmental Stress and Horticulture Crops
STEM DIELECTRIC CONSTANT MEASUREMENT AS AN INDICATOR OF PLANT WATER STRESS FOR FRUIT TREE IRRIGATION SCHEDULING |
| Author: | J. Bonany |
| Keywords: | Stem dielectric constant, Stem water content, Stem water potential apple, dendrometers, LVDT, transpiration |
| Abstract:
Several plant based measurements have been proposed as tools to schedule irrigation on fruit trees. Among others, leaf water potential, stem water potential (SWP) and Trunk Diameter Fluctuations (TDF) have been referenced as possible indicators of plant water stress. Usage of SWP, although very reliable are hindered because of lack of automation. TDF measured with automatic dendrometers, like Linear Variable Displacement Transducers, is probably the plant based measurement most often proposed although it has not yet gained wide practical acceptance due to the cost of the equipment and the difficulties of interpreting the provided data. While it has had much less attention, another indicator of plant water status is stem water content (SWC). Several authors have shown long term changes in SWC according to physiological changes and soil water availability. Few reports exist on short term changes of SWC or even diurnal changes following plant water relations linked to diurnal cycles of transpiration. Difficulties in direct measurement of SWC have prevented further utilization of this indicator. Recently, Time Domain Reflectometry and a diversity of different capacitive techniques, by measuring dielectric constant, have been used to estimate SWC. Experiments have been carried out with adult ‘Golden Delicious’ apple trees potted in 100 L containers with concomitant measurements of Stem Dielectric Constant (DCstem), SWP, TDF and Transpiration (T). Variations of Stem Dielectric Constant (DCstem) in different trees ranged from 32.5 to 22.7 when SWP varied from –0.2 MPa to –2.5 MPa. Hysteresis was observed in the relationship of SWP and DCstem. However a good relationship was noted between pre-dawn SWP, pre-dawn DCstem and Container Soil Water Content on days without irrigation. Data agrees with the hypothesis of DCstem being influenced by SWC. | |
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