Regional dynamics in evapotranspiration components, crop coefficients, and water productivity of vineyards

Estimation of water balance components, crop coefficients, and water productivity at multiple locations are crucial for understanding regional dynamics in irrigation requirement and efficient use of scarce water resources. These parameters were estimated for irrigated Shiraz vineyards over 3 consecutive seasons (2018–19–2020–21) at 48 locations in the Barossa, South Australia using the FAO-56 dual crop coefficient approach. Results showed large variability in water balance parameters, crop and water stress coefficients, and water productivity. A coefficient of variation ranging from 20 % to 97 % was observed in daily and seasonal actual evapotranspiration across sites and seasons. Average actual transpiration and evaporation account for around 63 and 37 % of the seasonal actual evapotranspiration, respectively, showing the potential to save water lost to the environment from the soil surface. Estimated actual single crop coefficient across all sites varied from 0.32 to 0.76, 0.35–0.59, 0.16–0.62 and 0.16–0.64 during the initial day (D60) to budburst (initial), budburst to flowering (mid1), flowering to veraison (mid2), and veraison to harvest (late) stages of crop growth, respectively. The actual basal crop coefficients for grapevine reveal considerable site-specific variability, questioning the value of adopting uniform coefficients across growth stages and at subregional and regional levels. Water stress gradually increased reaching its peak from late November to early December, with variations across the region ranging from 20 % to 64 %. A comparison of water productivities in relation to seasonal actual evapotranspiration and transpiration exhibits 60 % higher values for the latter across all the sites and subregions. Locally estimated crop coefficients will contribute to the efficient use of limited freshwater resources for sustainable wine grape production.