Effects of within-block canopy cover variability on water use efficiency of grapevines in the Sunraysia irrigation region, Australia

Irrigation methods commonly aim to match water supply to water requirement so that production outcomes are optimised. Grapevine water requirement estimates can be improved by adjusting crop coefficients for canopy cover (CC). Analysis of aerial images of 74 vineyard blocks revealed substantial ranges in CC between and within blocks. Within block variation compromises the ability to match water supply to water requirement at the sub block scale. Water losses (W-L) and yield penalties (Y-P) were modelled under two irrigation scenarios based on relationships between CC, water use and yield. These irrigation strategies aimed to match mean water use or maximum water use of grapevines within each block. While W-L and Y-P are driven by CC variability, W-L and Y-P were affected by CC and the irrigation strategy. Predicted W-L under irrigation to match maximum ETc were typically 25% of water supply, whereas irrigating to match mean ETc reduced W-L to less than 10% of water supply. Irrigating to match mean ETc penalised the grower, on average, 5% of potential yield. The model used in this study provides a basis for assessing impacts of CC variability in vineyards and evaluating options for improving water use efficiency at the block and sub-block scale.