Assessing AQUACROP water stress function to evaluate the transpiration reductions of olive tree.

Quantitative evaluation of the drought adaptation processes of crops is an important prerequisite for efficient irrigation management. Modeling the plant response under water stress conditions is crucial to identify the exact irrigation timing. Assessment of any water stress function requires the knowledge of its shape and then the estimation of critical thresholds of the soil water status, below which a strong reduction of plant transpiration occurs. In this work, the macroscopic approach is used to assess the water stress function implemented in AQUACROP for mature olive tree. In particular, after discussing about the function shape, the critical thresholds of soil water status are proposed according to experimental data. Eco-physiological measures (leaf and stem water potentials) were used as water stress indicators, whereas the relative depletion was considered as independent variable. The investigation evidenced, for the investigated crop, that a convex shape better reproduces the water stress function.