Variability in the Vineyard: A Multi‐Method Approach in Determining Grapevine Evapotranspiration Across Different Varietal Blocks

ABSTRACT Vineyards are highly heterogeneous systems where climate, soil, and management parameters can influence water loss by evapotranspiration (ET) across many spatial and temporal scales. To address vineyard variability of ET a multi‐method approach combining the use of in‐field atmometer ET gauges and the FAO‐56 dual crop coefficient procedure was employed. Spatial variability was addressed at two research sites in the Niagara (Ontario, Canada) growing region, Beamsville and Jordan, across three different cultivars: Chardonnay, Riesling, and Pinot Noir. It was hypothesised that variability in climatic controls including air temperature, precipitation, solar radiation, and wind dynamics would influence the variability in crop ET for each cultivar at both vineyards. Atmometer reference ET (ET 0 ) and water stress adjusted crop ET (ETcadj) were consistent for white cultivars across each study site. Pinot Noir grapevines, however, exhibited lower daily atmometer ET 0 , likely due to increased canopy shading or reduced wind turbulence to the canopy. The coefficient K cb , which accounts for transpiration, was consistent for all cultivars at both sites, while K e , the evaporation coefficient, showed a relationship between the soil water balance controlling water loss, especially regarding the Pinot Noir block. Water stress, represented by K s , was present at harvest for both Riesling blocks, and Beamsville Chardonnay and Pinot Noir, and was associated with optimal Brix concentrations, derived from the harvested grapes specific to each block. Overall, both vineyards showed importance between soil moisture and energy supplies with ET c adj , suggesting that changes in water and energy availability over the growing season are climatically significant to water loss and stress within each of the vineyard blocks. The use of atmometers in‐field, with adjustments by the FAO‐56 dual crop coefficient approach, is a simple and cost‐effective method that would allow growers to understand differences in vineyard‐scale meteorology and water loss by ET across multiple spatial and temporal scales within their vineyards.