LAUSR

Abstract Despite the fact that the pressure chamber has been used as a tool to assess vine water status and assist in scheduling vineyard irrigation for more than 30 years, there remains some disagreement in sampling protocol with respect to midday leaf water potential (Ψleaf) and midday stem water potential (Ψstem) determination. Therefore, the primary goal of this study was to test various sampling protocols associated with the measurement of these two variables. Specifically, experiments were conducted to test the effects of (1) re-cutting the petiole prior to placing the leaf in the chamber, (2) time span between sample excision and pressurization, (3) sample equilibration time on Ψstem values, and (4) the effect of operator. Results showed that there was no significant effect of re-cutting the petiole on Ψleaf values. Furthermore, up to 30 s of time span between sample excision and pressurization was acceptable for accurate Ψleaf determinations, as long as the sample was kept shaded during that time. Finally, only 10 min of equilibration time was necessary for accurate Ψstem determination. In most cases, the effect of operator on all Ψ determinations was greater than any of the sample preparation methods tested. This reinforces the need to properly train vineyard technicians in using the pressure chamber. However, improved flexibility in sampling protocol for either Ψleaf or Ψstem determinations may improve efficiency of vine water status monitoring in vineyards, thus reducing labor costs associated with pressure chamber-based irrigation scheduling.