Crop and stress coefficients in rainfed and deficit irrigation vineyards using sap flow techniques

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 _cb) and stress coefficients (K _s) 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 _cb) and plant water status (for K _s) is presented. K _cb, ranging from about 0.35 to 0.75, was highly correlated with leaf area index at stand level. K _s, which decreased till 0.2 in the most stressed vineyard, was well correlated to plant water status (K _s function), represented by predawn leaf water potential. K _s functions for the different experiments exhibited falling slopes with decreasing water status, with variable trends depending on the rates of maximal crop transpiration (T _m). These experimental results show that specific parameters for K _s functions, necessary to estimate water use and irrigation depths, in order to control the stress levels in DI scheduling, are also dependent on T _m.