Row orientation effects on potted-vines performance and water-use efficiency

The relation between water-use and intercepted solar radiation depends on many factors involved in vine canopy architecture and physiology. In addition, vine productivity is related to the efficiency with which the intercepted photosynthetically active radiation (IPAR) is used, which in turn depends mainly on water availability and transport. In hedgerow-managed vines it exists the possibility to modulate IPAR by orienting their rows, influencing water-use efficiency (WUE), defined as dry matter produced by water used. Aiming to unravel the effects of row orientation on WUE, a three-year experiment was carried out in Valencia (Spain) on potted Vitis vinifera (L.) cv. Bobal and Verdejo with vine rows oriented either north-south (NS) or east-west (EW), under no-water restrictions. Simulated radiation interception over the growing seasons at the experimental plot showed an average 39% reduction in daily IPAR when EW was compared to NS. Vine transpiration was quantified by water balance, decreasing by 16% in Bobal and 8% in Verdejo when comparing EW against NS. In both cultivars, this reduction was 18% when considered relative to the total leaf area. Carbon assimilation was not markedly affected by row orientation. Therefore, since in both cultivars minor differences in vine performance occurred between orientations, WUE tended to increase by orienting the rows to the EW compared to NS. This resulted in most of the seasons an increase in water productivity calculated as grape yield/water-use ratio. Leaf gas exchange measurements partially agreed with the radiation interception simulations, suggesting a more complex regulatory mechanism and highlighting the importance of canopy microclimatic conditions in the physiological processes of hedgerow-managed crops. These findings encourage further research under field conditions and different soil water availabilities, aiming to optimize grapevine water productivity.