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

Abstract

AbstractEstimation of water balance components, water stress and crop coefficients at different spatial locations within a region are the crucial indicators for understanding regional dynamics in irrigation requirement and crop water use. We estimated the evapotranspiration (ET) components, crop coefficients and seasonal water stress coefficients for vineyards at 48 locations over 3 consecutive seasons (2018-19, 2019-20 and 2020-21) in the Barossa region using FAO-56 dual crop coefficient approach. Relevant data for soil, crop and climate parameters were collected at 48 locations across the region during three vintages (2019-21). Modelled daily dynamics of plant available water (PAW) in the soil were compared with the measured values from capacitance probes installed at each site. Estimated season values of actual evapotranspiration and actual transpiration were used to estimate the crop biomass and grain water productivities in the study region. Statistical error estimates and efficiency parameters between measured and modelled daily plant available water (PAW) in the soil profile showed a good agreement across the study sites and seasons indicating reliable prediction by FAO-56 approach.Results showed a high variability ranging from 20 to 97% in the daily actual ET (ETc act) values and seasonalETc actvaried from 119-546 mm across different sites and seasons. Average actual transpiration (Tc act) and evaporation (Es) across the region accounts for around 65 and 35% of theETc act, respectively, showing a need for better management of water lost to 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) stage of crop growth, respectively showing a variation ranging from 3 to 56%. Similarly, average actual basal crop coefficients (Kcb act) for grapevine during the initial, mid- and end period ranged between 0.17-0.24, 0.24-0.31, and 0.12-0.36, respectively across different sub-regions. The extent of water stress (Ks) increased gradually and attained maximum level during the late November to early December period showing a deviation between 23 to 64% across the region. Variations in the components of ET and crop coefficients are consistent with the variation in soil, topography and microclimates that characterise this region. Locally estimatedKc actandKcb actwill contribute to the efficient use of limited freshwater resources for sustainable wine grapes production in the study region.