Improvement of yield and grape and wine composition in field-grown Monastrell grapevines by partial root zone irrigation, in comparison with regulated deficit irrigation

Regulated deficit irrigation (RDI) and partial root zone irrigation (PRI) were compared for four years (2009-2012), each at two different irrigation volumes (110 mm year−1 (1) and 78 mm year−1 (2)), in field-grown Monastrell grapevines grafted onto 1103P, in South Eastern Spain. The aim was to distinguish the effects of deficit irrigation per se from specific PRI effects (placement of water) on yield response and berry and wine quality. Vines grown with PRI-1 or RDI-1 received around 30% of the ETc from budburst to fruit set, 13-15% ETc from fruit set to véraison and 20% ETc from véraison to harvest. The RDI-2 and PRI-2 vines received around 20% ETc from budburst to fruit set, no irrigation from fruit set to véraison and a recovery (21-24% ETc) thereafter. In general, the PRI-2 and RDI-2 vines (the most-severely water-stressed) showed greater yield reduction and lower overall berry and wine quality (including technological and phenolic composition) than the moderately-water-stressed vines (RDI-1 and PRI-1). Compared to RDI-1, PRI-1 improved the yield response-increasing mean yield, cluster number per vine and berry weight and maintaining better bunch health at late ripening and a greater proportion of bigger bunches. In addition, PRI-1 increased the anthocyanin and amino acid concentrations of the berries and altered their composition, improving the phenolic and chromatic characteristics of the wine and enhancing the health-promoting value of the fruit. It was also the option most economically viable under the present conditions of the wine grape market, compared to RDI-1 and the rest of the treatments. In contrast, PRI-2, although it improved some technological quality attributes and phenolic and chromatic characteristics of Monastrell berries and wines compared to RDI-2, did not have a positive effect on yield (yield and cluster and berry weight decreased in some years) and its implementation was economically unviable under these soil and climatic conditions. The significant interaction between irrigation volume (high vs. low) and irrigation placement (PRI vs. RDI) indicate that the response to PRI also depended on the volume of water applied in the wet root zone and the soil total water availability.