Commonly used water requirement estimations for irrigation scheduling are not adequate under stressed conditions, being thought for complete water completion requirements. New trends are emerging, linked to the dramatically growing water scarcity problem. These trends are promoting deficit irrigation approaches that need new approaches for evaluating water needs under stressed conditions. It is the reason why a "plant approach" is also necessary, in order to estimate its real needs, up-scaling them to the total plant community (field, orchard, forest). Sap flow methods are among the most promising tools. With the Granier method (1985, 1987) that presents interesting operational and cost advantages it is possible to increase the number of trees for appropriate sampling and to make long term cheap measurements. The comparison between eddy covariance data sets (EC) and sap flow estimates (SF) provided experimental evidence of underestimation from SF measurements using the original Granier calibration equation, for all the conditions shown here. A correction allowed an adjustment of the sap flow measurements, obtaining transpiration data for the duration of the vegetative cycles. RT and stress coefficients could also be calculated from SF measurements and related with water stress indicators. Due to the complexity of the interpretation on water stress indicators, it appears that not only an isolated variable but its combination with simultaneous observations on water use and water stress indicators provide some answers useful for scheduling irrigation.
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