Sheep manure: An effective regenerative practice for enhancing Plavac Mali (Vitis vinifera L.) wine quality in dry-farming vineyards on Hvar island

Abstract

There is an urgent need to develop protective measures for grapevines in historically significant dry-farming vineyards, particularly on Mediterranean islands. Despite the importance, the impact of regenerative viticulture practices in severe drought agroecological conditions remains poorly understood.

The aim of this study was to explore the impact of three regenerative practices on the physicochemical and phenolic properties of Plavac Mali wines from two vineyards (Vin_A and Vin_B) on south sunny slopes of Hvar Island, Dalmatia. Vin_A, at 160 m with a 34% slope, produces lower quality grapes than Vin_B, at 350 m with a steeper 55% slope that experiences cooler conditions producing more acidic grapes. Organic sheep manure (3 kg per vine), straw mulching at 30 cm, and seactive biostimulanting organic complex applications (pre-flowering, post-fertilization, and berry coloration), were compared to an untreated control. Two vineyards showed different trends with more pronounced changes in wine composition in Vin_A situated at lower altitudes. Regenerative practices had a significant impact on the physiochemical composition of wine in Vin_A. The wines of the biostimulant treatments had a significantly higher total and volatile acidity, reducing sugars compared to all, and alcohol compared to manure and mulch treatments. The biostimulant treatment wines had a significantly higher concentration of hydroxybenzoic, gallic acid, and hydroxycinnamic, caffeic acid, and lower quercetin in comparison to other treatments. The wines of manure and mulch treatments had significantly lower concentrations of catechin-derivative, epicatechin, and ECGC, compared to control.

In Vin_B biostimulant and manure treatment wines had significantly lower concentration of gallic acid and EK in comparison to mulch treatments, and protocatechic acid and EGCG in comparison to mulch and control treatments. The regenerative viticulture practices can significantly influence the physicochemical and phenolic profiles of Plavac Mali wines, with effects varying depending on vineyard-specific factors. The manure and mulch treatment were more effective in decreasing bitter and astringent compounds in wines of VIN_A, and biostimulants and manure treatments were more effective in VIN_B. These findings underscore the potential of regenerative practices in the improvement of grapevine resilience under drought stress while enhancing the polyphenolic composition and sensory quality of wines.