The Effect of Supplemental Irrigation on a Dry-Farmed Vitis vinifera L. cv. Zinfandel Vineyard as a Function of Vine Age

Abstract

With natural rainfall and surface water availability becoming scarce, prolonged droughts are expected to become more frequent, thereby creating issues for agriculture. In viticulture, a lack of rainfall is often supplemented with irrigation during the growing season and/or dormancy. However, with surface and groundwater resources declining in addition to current changes in rainfall patterns, it is unlikely that supplemental irrigation will continue to be an available tool for most growers. As such, this study aims to evaluate the effect of dry farming and supplemental irrigation during the growing season on vine performance and fruit composition as a function of vine age in Zinfandel grapevines. A historically dry-farmed vineyard block with interplanted vines of varying ages was evaluated during the 2021 growing season. Treatments included young vines (5–12 years old), control vines (2:1 ratio of old to young vines representative of the block), and old vines (40–60 years old); each age designation included irrigated and dry-farmed vines. Based on age-specific ETc and to replenish 95% of crop evapotranspiration (ETc), irrigation was manually applied to the irrigated treatment vines at véraison and véraison + 4 weeks. Results indicated no significant changes in phenological progression, leaf senescence, or physical berry analysis when irrigation was added to dry-farmed vines, as most differences were driven by vine age in most parameters measured. Irrigated vines were slightly more advanced in phenological growth and senescence progression compared to dry-farmed vines. Results suggest that the practice of applying supplemental irrigation during the growing season, provided winter rainfall or additional winter irrigation is sufficient, does not have significant impacts on vine performance. Thus, dry farming during the growing season is a reasonable alternative practice in Zinfandel, even in periods of drought.