Use of water potential measurements for assessing water stress in Vitis vinifera L. cv. Tempranillo grown in Southern Oregon

Abstract

A study was conducted to investigate the practical use of four methods for measuring the plant water potential (Ψ) of Vitis vinifera L. cv. Tempranillo under field conditions within the Southern Oregon American Viticultural Area (AVA). Predawn leaf water potential (Ψpd), midday leaf water potential (Ψl-md), midday stem water potential (Ψs-md) and early morning stem water potential (Ψs-em) were each measured on vine before and after the initiation of irrigation. Irrigation treatments were as following: 70% of ETc for the entire growing season, 35% of ETc for the entire growing season, 70% ETc before veraison and 35% ETc after veraison, and 35% before veraison and 70% ETc after veraison. When assessing vineyard variability before the initiation of irrigation, with Ψpd ranging between -0.05 MPa and -0.53 MPa, it was found significant differences among locations within the experimental block, and the vines could be categorised under previously established thresholds on all four water potential parameters. When Ψl-md was greater than -0.9 MPa there was a tendency to underestimate the vine water status. When comparing Ψs-em, Ψs-md and Ψl-md, early morning measurements showed significant differences between irrigation treatments on 3 of 4 measurement dates while following midday measurements significant differences on only 1 of 4 dates were found. Even on cloudy days measuring the Ψs-em it was possible to distinguish differences among vines with diferent water status. In this study, Ψs-em data indicated that this parameter might be used with confidence in water management decision process in vineyards.