Relationships among Vine- and Soil-Based Measures of Water Status in a Thompson Seedless Vineyard in Response to High-Frequency Drip Irrigation

Abstract

A study was conducted in the field on Vitis vinifera L. (cv. Thompson Seedless) to compare various measurements of vine water status under high-frequency drip irrigation. Water use at 100% of vine evapotranspiration (ET_c), was determined with a weighing lysimeter. Vines in the vineyard were irrigated at 0, 0.2, 0.6, 1.0, or 1.4 times the amount of water used by the lysimeter vines. Water applications occurred each time the lysimeter lost 16 L of water (2 mm depth; 8 L vine⁻¹). Soil water content (𝛉_v) was measured in the 0.2, 0.6, 1.0, and 1.4 irrigation treatments. Predawn (Ψ_PD), midday leaf (Ψ_l), and midday stem (Ψ_stem) water potentials were measured at the ends of the 1991 and 1992 growing seasons and almost monthly during 1993. Soil water content in 1993 remained constant throughout the growing season for the 1.0 irrigation treatment, increased in the 1.4 treatment, and decreased in the 0.2 and 0.6 treatments. Both Ψ_l and Ψ_stem measurements detected differences among irrigation treatments to a greater extent than did Ψ_PD until very late in the 1993 growing season. There was a linear relationship between Ψ_l and Ψ_stem. All three measurements of water potential were related to soil water content (using a quadratic function); however, the relationship between SWC and Ψ_PD had the lowest R² value, 0.52 compared to 0.90 and 0.94 for Ψ_l and Ψ_stem, respectively. Results indicated that Ψ_PD would not be useful in accurately determining vine water status under high-frequency deficit irrigation.