Using ΔC13 to assess viticultural and oenological suitability for Sangiovese of different pedoclimatic conditions in Chianti

A two years trial was carried out in Chianti (Central Italy) to assess at the detailed scale the viticultural and oenological suitability for Sangiovese of different pedoclimatic conditions, by means of the ΔC13 measured in the must sugars. Six plots placed in two specialised vineyards in similar geomorphological conditions were investigated. The plots differed for morphological position: summit, backslope and footslope. The soils of the vineyards were similar, except for structure, porosity and related hydropedological characteristics. Soil water content and temperature were measured at different depths. Measurements were replicated every one/two weeks. Soil characterization included macroporosity quantification by image analysis.
The yield, phenological phases, and chemical analysis of grapes were determined. The isotopic ratio 13C/12C was measured in the must sugar upon harvesting. Grapes of each plot were collected for wine making in small barrels. The wines obtained were analysed and submitted to a blind organoleptic testing.
The results demonstrated that almost all plots had rather high amounts of transpirable water, even during the driest time of the year; however, the response of Sangiovese was influenced by site hydropedology. The soils in morphological positions receiving and holding more water produced significant worst results in the moister 2005, than during the drier 2006. The drier soils yielded the best results in both years, but more prominently in 2005. Vines of the plots having a lower soil water availability produced relatively higher values of ΔC13, as well as a better oenological and organoleptic result. The ΔC13 test confirmed the limited stress conditions in the two vineyards, despite yields in the two years ranged from 2 to 8 kg per plant. This result highlighted the pedoclimatic limitations of the studied sites in obtaining high quality wine.