Mapping suitability for Sangiovese wine by means of δ ¹³C and geophysical sensors in soils with moderate salinity

A three year experiment was carried out to test the possibility of using the carbon isotope ratio (δ ¹³C) measured in wine, combined with data of proximal and remote soil sensors, to assess viticultural and oenological suitability for Sangiovese. Two specialized vineyards on similar geomorphological conditions were investigated. Twelve plots were positioned differently along slopes. The soils were similar, except for structure, porosity and related hydrological characteristics, and salinity of the deeper horizons. Soil electrical conductivity and resistivity were measured at three different depths, as well as cumulative soil moisture down to the root-limiting layer. Satellite images were analyzed to obtain the NDVI. Soil water content in the plots was monitored at different depths. Yield, phenological phases, and chemical analysis of grapes were determined. Stem water potential was measured during summer. Grapes of each plot were collected for wine making in small barrels. The wines obtained were analyzed and submitted to a blind organoleptic testing. The wine was also analyzed for its δ ¹³C isotopic ratio. Almost all plots had rather high amounts of transpirable water, even during the driest time of the year. However, only yield components of Sangiovese were influenced by water availability. Wine quality was instead significantly improved by the moderate salinity of the deeper horizons, which increased plant water stress during berry ripening and reduced production. The moderate physiological stress affecting vines was reflected in stem water potentials and δ ¹³C values. δ ¹³C was correlated with several viticultural and oenological parameters, and also with panel test evaluations of wine quality. The threshold between good and bad scores corresponded to a δ ¹³C value of −26.7±1.2‰. Soil salinity affected the geophysical survey and its relationship with the viticultural and oenological result. In particular, the electromagnetic conductivity measured at the beginning of the experiment was functional in distinguishing the two vineyards, but it was not useful for a more detailed prediction of Sangiovese performance. However, electromagnetic resistivity in the first 0.5m was not influenced by salinity of the deep soil horizons, but only by clay content, and permitted a significant estimation of the Sangiovese anthocyanins content, colour intensity, and must acidity. The outcomes of this study recommend the use of δ ¹³C in combination with electromagnetic resistivity to map soil suitability for Sangiovese. The favourable performance of Sangiovese in moderately saline soils may encourage diffusion of the cultivar outside its traditional areas of cultivation.