Preliminary results of the water use and performance of grapevine cultivars in response to crop load and water replenishment from the subsoil under a warm temperate climate

Abstract

Climate change is making rainfall less predictable, sparking uncertainty for producers regarding the availability of water for irrigated and dryland (rainfed) vineyards in the future. By investigating how rainfed vineyards react under different crop load levels and examining how water is supplied via the subsoil, we can provide valuable guidance for managing vineyards under harsher conditions. In 2018, a rainfed vineyard trial was established with 17 different cultivars (all rooted on 99 Richter rootstock) planted in a randomised block design. In this experiment, the eight highest-yielding cultivars (Pinotage, Marselan, Vermentino, Macabeo, Chenin blanc, Piquepoul blanc, Grenache noir, and Durif) were chosen to assess three different crop load levels. Crop loads were applied just after the bunches reached the phenological stage of pea size. The crop loads applied were keep every bunch on the vine, 35% crop removal, and the removal of every. The sub-surface soil water content was also monitored via six strategically placed 1.5 m long continuous logging probes. The plant water status was also measured (full sun leaf water potential and midday stem water potential) immediately before harvest. Chenin blanc showed a significant decrease in bunch mass between the 100% and 35% crop load treatments. None of the other cultivars showed a significant difference in bunch mass between the two crop loads. Mixed results were found when the plant water status was measured, which could be attributed to a decrease in leaf area over the season and/or a reduction in crop load. The findings of this study could practically and scientifically contribute to the understanding of how grapevines react under rainfed conditions when different crop loads are applied. This study could also contribute to understanding the role of the possible overcropping of grapevines under rainfed conditions.