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Aims: In this study on hydraulic redistribution (HR) in roots, we aimed to use the calibrated average-gradient (CAG) heat-pulse method, the novelty being the use of a much narrower averaging window for the signal analysis, in order to achieve a more linear calibration curve, allowing the HR quantification.Methods: The study was conducted in 12 large roots of a rain-fed olive orchard, for 6 months without significant rain, when the predawn leaf water potential decreased to −2.4 MPa, and immediately following the first autumn rains.Results: Detailed numerical modelling of the CAG method allowed verification of the response of the measurement system to a range of drivers, improving the linear range of the calibration response function, which has remained stable over the observations period. On average, reverse flow was observed during 30% of the summer nights and, in a conservative estimate, it increased to about 5% of total daily root flow before first autumn rain.Conclusions: Reverse flow accounted on average for 2.6% of the total daily root flow, enabling upper roots to stay active during the very dry late-summer period. In qualitative terms, our results confirm the CAG method as a reliable tool to identify reverse flow and quantify HR when it occurs. [ABSTRACT FROM AUTHOR]

Projected climate changes and expansion of viticulture to drier regions justify the installation and management of deficit irrigation (DI) strategies. Contradictory results on the effect of DI on crops may be ascribed to the incorrect application of these techniques. The lack of discrimination between basal crop ( K) and stress coefficients ( K) can be an obstacle to proper irrigation management. A sap flow (SF) technique associated with microlysimeters and eddy covariance (EC) methods was applied to five commercial vineyards, aiming to discriminate those coefficients, during the driest period of the vegetative cycle. A comparative analysis of the coefficients, in relation to measured vegetation parameters (for K) and plant water status (for K) is presented. K, ranging from about 0.35 to 0.75, was highly correlated with leaf area index at stand level. K, which decreased till 0.2 in the most stressed vineyard, was well correlated to plant water status ( K function), represented by predawn leaf water potential. K functions for the different experiments exhibited falling slopes with decreasing water status, with variable trends depending on the rates of maximal crop transpiration ( T). These experimental results show that specific parameters for K functions, necessary to estimate water use and irrigation depths, in order to control the stress levels in DI scheduling, are also dependent on T. [ABSTRACT FROM AUTHOR]