Can continuous records with plant-based methods be used to estimate water stress intensity in deficit irrigated vineyards?

Abstract

Vineyards are traditionally rainfed in Portugal. However, in drier and southern regions (e.g. Alentejo) water supply by irrigation is increasingly being used. Deficit irrigation (DI) strategies are mandatory due to the relationships between vineyard water status and crop yield and wine quality. For a proper DI management we evaluated the use of sap flow (SF) to get transpiration (T) in relation to crop evapotranspiration (ETc), trunk diameter variation (TDV) and leaf water potential measurements for assessing water stress intensity. Leaf water potential was measured at predawn (PLWP) and stem water potential (SWP) at solar noon. Data obtained using the thermal heat dissipation SF technique was corrected locally against eddy covariance measurements. Three TDV derived indicators, maximum daily shrinkage, daily growth and daily recovery were evaluated. The experiment was done in a commercial DI vineyard, cv. Tempranillo, at the Portuguese Alentejo region. Three deficit irrigation intensities were imposed after veraison. For operational reasons, during 2009 growing season irrigation levels were defined as 70%, 40% and 25% of ETc approximately, with crop coefficient (Kc) estimated as a function of leaf area index. The analysis of the relationship between T/ETc and leaf water potential suggested that PLWP was, in these experimental conditions, a better water stress indicator than SWP. The TDV indices were sensitive to irrigation but did not discriminate between the different irrigation treatments. Rather, SF data allowed a proper discrimination of the irrigation treatments applied, reinforcing the interest of sap flow techniques, if properly corrected, for irrigation management applications, as they provide information both on water stress and on water use.