Effects of post-veraison irrigation regime on Cabernet Sauvignon grapevines in Valencia, Spain: Yield and grape composition

Abstract

In the old-world viticulture, there is a common but most often not scientifically proven consideration that supplemental irrigation should detrimentally affect berry and wine composition. In the temperate-warm climate of inland Valencia (Spain), during three growing seasons (2009–2011), the effects of post-veraison deficit irrigation regime on Cabernet Sauvignon vine performance and berry composition were determined. Rainfed vines were compared with three post-veraison deficit irrigation regimes replacing 25, 50 and 75% of the estimated crop evapotranspiration, resulting in water application of 37, 67 and 128mm, respectively. Rainfed vines experienced quite severe plant water stress, reaching, in two out of the three experimental seasons, midday stem water potential values as low as −1.6MPa. Despite this, rainfed vines at harvest had the highest concentration of berry total soluble solids and phenolics among all tested water regimes. This was most likely a consequence of berry dehydration which, in the rainfed vines, resulted in a reduction of berry size, while in the irrigated treatments a constant increase in fresh berry weight was observed during the ripening period. As a consequence, the two greater irrigated treatments resulted in a 26–30% yield increase. In addition, when replacing half of the potential water needs, total water use efficiency could be maintained at similar levels as in rainfed vines. In any case, the main positive effect of the supplemental irrigation application was to avoid the excessive increase in berry sugar content, which at commercial vintage time reached up to 16.5% of probable alcohol in the rainfed treatment. It is therefore concluded that moderate post-veraison irrigation water application might result in a more balanced sugars-phenolics grape composition while considerably increasing yield in comparison with the rainfed regime. In any case, the most convenient irrigation strategy might depend on the desired grape style and, indeed, on wine consumer preferences