Determination of Evapotranspiration and Crop Coefficients for a Chardonnay Vineyard Located in a Cool Climate

Abstract

A study was conducted in a Chardonnay vineyard located in the Carneros district of Napa Valley to derive vineyard evapotranspiration (ET c ) and seasonal crop coefficients (K c ) values. The vineyard was planted on 2.13 m rows, using a vertical shoot-positioned trellis. Vineyard ET c was measured using the soil water balance method. Soil water content (SWC) was measured in one-fourth of an individual vine’s soil profile (six access tubes per site) to a depth of 2.75 m. In addition, vines were irrigated with applied water amounts at 0.25, 0.5, 0.75, 1.0, and 1.25 of estimated vineyard ET c . Vineyard ET c the first year of the study was ~400 mm. Thereafter calculated vineyard ET c (the product of reference ET [ET o ] and the K c ) ranged from 346 to 503 mm per season. Midday leaf water potential (Ψ l ), leaf net CO 2 assimilation rate (A), and stomatal conductance (g s ) were used to indirectly validate estimated ET c (to determine that vines were not stressed for water) and the derived K c values. Midday Ψ l , A, and g s were linearly related with applied water amounts and SWC across irrigation treatments and years. The diurnal measurements of A and g s resulted in differences among irrigation treatments, from early morning until late afternoon, with significant differences among treatments dependent upon actual applied water amounts. The results from this study are the first in which vineyard ET c has been measured on vines grown at a cool vineyard site in California. Estimates of ET c from this study would be valid for a vineyard with a row spacing of 2.13 m and a canopy vertically positioned using a maximum K c of 0.74.