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

Estimation of water balance components, water stress and crop coefficients at different spatial scale are crucial for understanding regional dynamics in irrigation requirement and crop water use. We estimated these parameters for irrigated vineyards over 3 consecutive seasons (2018-19, 2019-20 and 2020-21) at 48 locations in the Barossa region, South Australia. We used FAO-56 dual crop coefficient approach by integrating relevant data for soil, crop, and climate parameters from the study sites. Numerous statistical error estimates, and efficiency parameters were estimated to compare and verify the predictions by FAO-56 approach. Results show a huge variability in the irrigation, water balance parameters, crop and water stress coefficients, and water productivity parameters. For instance, a coefficient of variation ranging from 20 to 97% was observed in daily and seasonal actual ET (ETc act) across different sites and seasons. Average actual transpiration (Tp act) and evaporation (Es) account for around 65 and 35% of the ETc act, respectively, showing the potential to save water lost to the environment from the soil surface. Estimated actual single crop coefficient (Kc act) across all sites varied from 0.35 to 0.59, 0.16-0.62 and 0.18-0.68 during the budburst to flowering (BB-FL), flowering to veraison (FL-V), and veraison to harvest (V-H) stages of crop growth, respectively. Similarly, actual basal crop coefficients (Kcb act) for grapevine reveal immense site-specific variability questioning the adoption of uniform coefficients at subregional and regional levels. Results further demonstrate that water stress (Ks) gradually increased reaching its peak from late November to early December, with variations across the region ranging from 23 to 64%. A comparison of water productivities in relation to ETc act and Tp act exhibit almost 61% higher values for the latter across all the sites and subregions. Dry biomass productivity shows huge potential for renewal energy generation. Variations in the components of ET and crop coefficients are consistent with the characteristic variation in soil, topography, and microclimates. This study suggests that locally estimated Kc act and Kcb act will contribute to the efficient use of limited freshwater resources for sustainable wine grape production.