Usefulness of early morning stem water potential as a sensitive indicator of water status of deficit-irrigated grapevines (Vitis vinifera L.)

• Stem water potential is a reliable method of measuring the water status of plants and trees, including grapevines.
• Early morning measurements of stem water potential have been shown to have high sensitivity to water stress.
• This technique may be useful for establishing irrigation scheduling thresholds in irrigated vineyards and orchards.

A study was conducted to investigate the practical use of early morning stem water potential (Ψstem-em) as a measure of water status of Vitis vinifera L. cv. Tempranillo under field conditions within the Southern Oregon American Viticultural Area (AVA). Midday leaf water potential (Ψleaf-md), midday stem water potential (Ψstem-md), and Ψstem-em were each measured on vines being irrigated at 70% of crop evapotranspiration (ETc) and 35% of ETc. Predawn leaf water potential (Ψpd) and Ψstem-em were also measured on the same cultivar with the same irrigation treatments at a different vineyard within the same AVA. In comparing Ψleaf-md, Ψstem-md, and Ψstem-em over the growing season, early morning measurements showed differences between irrigation treatments on three of four measurement dates while midday measurements on the same vines showed differences on only one of four dates. Linear regression analysis of Ψstem-em versus Ψpd, Ψstem-md, and Ψleaf-md indicated significant positive correlations. Ψstem-em measurements also had a high degree of repeatability as indicted by their low coefficients of variance. The results of this study indicate that Ψstem-em could be a useful parameter for the assessment of grapevine water status due to its high sensitivity compared to other commonly used metrics.