Suitability of pre-dawn and stem water potential as indicators of vineyard water status in cv. Tempranillo

Abstract

Background and Aims: Irrigation management requires the collection of up-to-date information that allow growers to make rapid decisions, water potential being one of the most used parameters in irrigation scheduling. The goal of this research was to determine whether predawn (Ypd) and stem (Ys) water potential can be used equally well, quantifying the effect external factors have on the relationship between them. Methods and Results: Ypd, mid-morning (Ys-m) and noon (Ys-n) stem water potential were measured at seven cv. Tempranillo vineyards. Climatic conditions, vine growth and fruit load affected daily water potential dynamics. A greater decline of Ys occurred when temperatures were higher and there was no dew formation, as well as under larger canopies and fruit load. While the relative impact of these variables on water potential was not particularly high, it was by no means negligible. Conclusions: Data collected in this study did not favour Ypd, Ys-m or Ys-n as a preferred measure to evaluate plant water status. It is important to remark that similar Ypd values do not necessarily indicate the same level of deficit, and that similar Ys values do not always mean similar water availability. Therefore, a straightforward interpretation of Ypd and Ys can sometimes be misleading. Significance of the Study: The results obtained provide significant explanation to the lack of agreement in the literature regarding the most suitable time to measure water potential. Vineyard managers and scientists should select it according to the level of stress expected, climatic conditions and irrigation frequency. Abbreviations BN berry number; DR discriminating ratio; ET evapotranspiration; LWD leaf wetness duration; YL leaf water potential; Ypd pre-dawn leaf water potential; Ys-m mid-morning stem water potential; Ys-n stem water potential at noon; SBA sum of shoot basal cross-sectional area; VPD vapour pressure deficit.