EVAPOTRANSPIRATION AND WATER RELATIONS FROM A VINEYARD IN CENTRAL PORTUGAL DURING SPRING-SUMMER PERIODS

Evapotranspiration (ET), transpiration (T) and some water stress indicators were followed during 96 and 97. One of the aims was the quantification of the water consumption for subsequent modelling. Another important objective was to improve the understanding of the time evolution of T during periods of progressively high water deficit, assessing the role of the main controlling factors. T was measured with sap flow techniques and ET with eddy covariance method, during limited periods. Environmental variables and reference evapotranspiration (ETo) were also followed. The relationship between predawn leaf water potential (psip) and stomatal conductance (gs) at noon, and between those variables and T/ETo are discussed, as well as the seasonal trend of T/ETo. The results show that the relationship ET/ETo ranges between about 0.83 and 0.17 and T/ETo between 0.60 and 0.16. There is a good relationship between psip and gs with a threshold value about -0.35 MPa.