https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1834&context=usdaarsfacpub

Evapotranspiration information reporting: I. Factors governing measurement accuracy

Trees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87% of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water-stress induced cavitation. These data are discussed in the context of the plant segmentation hypothesis.

Drought‐induced leaf shedding in walnut: evidence for vulnerability segmentation

Research in estimating the water status of crops is increasingly based on plant responses to water stress. Several indicators can now be used to estimate this response, the most widely available of which is leaf water potential (ΨLWP) as measured with a pressure chamber. For many annual crops, the predawn leaf water potential (ΨPLWP), assumed to represent the mean soil water potential next to the roots, is closely correlated to the relative transpiration rate, RT. A similar correlation also holds for young fruit trees grown in containers. However, exceptions to this rule are common when soil water content is markedly heterogeneous.

Significance and limits in the use of predawn leaf water potential for tree irrigation

Sponsored by the Committee on Evapotranspiration in Irrigation and Hydrology of the Irrigation and Drainage Council of the Environmental and Water Resources Institute of ASCE Evaporation, Evapotran...

Evaporation, Evapotranspiration, and Irrigation Water Requirements

Measurement and modelling of evapotranspiration of irrigated citrus orchard under Mediterranean conditions

it is assumed that the heat flow between the trunk surface and the surrounding air is negligible. The method was tested : a) in the laboratory, by forcing water passage in a branch segment under stationary conditions and by comparing these known water fluxes with the estimated values; b) in the greenhouse, with small potted trees (1 - 8 cm diameter), by comparing the actual transpiration rate measured by weighing and the estimated values. The experimental results indicate that the computed sap flow rate closely follows the measured transpiration rate and the daily transpiration flow is evaluated by excess with a variable error not greater than 30%. Analysis of the results shows that this method can be improved by measuring the lateral heat flow and the heat power accumulated in the volume of trunk limited by the heating jacket An improved sap flow sensor is now being tested.

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Z. Nasr

Papers

Une méthode de mesure du débit de sève brute dans de petits arbres par bilan de chaleur