Monitoring of irrigation in a Mediterranean vineyard: water balance simulation versus pressure chamber measurement.
Résumé
Irrigation may be needed in the Mediterranean context but the monitoring of the grapevine water stress and the calculation of the irrigation needs are subject to difficulties. To obtain a specific yield and quality of the harvest, a defined course of water potential, ranging typically from – 0.1 MPa to – 0.6 MPa, is targeted by the wine grower. In the Mediterranean context, intense water stress (very negative values of potential) at inappropriate times is possible; it can be avoided by supplying irrigation. The traditional diagnosis method based on predawn water potential measurement requires sampling numerous leaves at night. Another approach is based on the utilization of a water balance model, which includes the regulation of transpiration performed by the grapevine, together with the physical processes occurring in the field: bare soil evaporation and runoff. The soil reservoir is characterized by its Total Transpirable Soil Water, and the maximal grapevine transpiration by a crop coefficient calculated from the geometrical parameters of the vegetation. In the experiment reported here (domaine Cazes, Rivesaltes, France), irrigation was triggered by comparing the calculated grapevine status with successive thresholds of potential in adequation with an objective of yield and quality. The parameters (Total Transpirable Soil Water, runoff curve number, readily and totally evaporable water, crop coefficient) were calculated from field and grapevine observations, and climatic data came from the nearby meteorological station. Total Transpirable Soil Water was estimated at 145 mm from profiles of water content and cultural profile (root distribution) performed in the vineyard, and the crop coefficient for Cabernet vineyard attained 0.47. The pressure chamber monitoring led to 30 mm (three time 10 mm) irrigation both in 2010 and 2011. The water balance model would have led to 50 mm in 2010 and 30 mm in 2011. These results are considered promising for the water balance monitoring of irrigation at the field scale.