Use of the water balance model Walis to predict stem water potential on colombard variety in Gascony vineyard

Abstract

WaLIS (Water Balance for Intercropped Systems) is a model that carries out the daily evolution of the soil water content. It takes into account the water requirement of a grass cover crop in competition with the grapevine. There is a relation between the Fraction of Transpirable Soil Water (FTSW) measured or performed by model, and the predawn water potential (y_p) which is a base indicator of the vine water status. In Gascony vineyard (south west of France), under oceanic climate, the vine water status generally presents weak to moderate deficit. The main indicator used is the stem water potential (y_stem). The aim of this study was to apply the WaLIS model to predict stem water potential on Colombard variety in moderate water stress conditions. The indicators (FTSW, y_p, y_stem) has been linked to five classes of vine water status. Then, the relation y_p = f(FTSW), already published, has been transformed in y_stem= f(FTSW).The model has been parameterized to produce y_stem data. Next, we measured y_stem on 3 irrigation trials (with and without water supply) during 3 vintages, 2010 to 2012. The results showed a correct prediction in order to simply classify the vine water status. The model slightly underestimated the measured values. This tool could allow to diagnostic at vineyard scale the water deficit zones in relation with the wine profile expected. It could also be used to monitor the irrigation.