Geostatistical analysis of the vineyards in the canton of Geneva in relation to soil and climate

The production of Port Wine requires the addition of grape spirit to stop the fermentation, ensuring the desired sweetness

La mesure de la résistivité électrique des sols est une technique non destructive, spatialement intégrante, utilisée depuis peu en viticulture. L’utilisation d’appareils de mesures performant et de logiciels adaptés permet de traiter les données afin de pouvoir visualiser en deux ou trois dimensions les variations de textures ou d’humidité d’un sol.

L’A.O.C. Coteaux du Languedoc est située dans le Sud de la France, dans la partie Ouest de la bordure méditerranéenne. Elle forme un vaste amphithéâtre largement ouvert sur la mer méditerranée. L’Appellation a été constituée en 1960 par le regroupement de 14 anciennes petites appellations d’origine représentant 55 communes éparpillées dans les départements de l’Aude, de l’Hérault et du Gard. Par la suite, plusieurs extensions successives ont conduit à un ensemble actuellement composé de 168 communes.

The current climate changes are directly threatening the balance of the vineyard at harvest time. The maturation period of the grapes is shifted to the middle of the summer, at a time when radiation and air temperature are at their maximum. In this context, the implementation of corrective practices becomes problematic. Unfortunately, our knowledge of the climate effect on the quality of different grape varieties remains very incomplete to guide these choices. During the Innovine project, original experiments were carried out on Syrah to study the combined effects of normal or high air temperature and varying degrees of exposure of the berries to the sun. Berries subjected to these different conditions were sampled and analyzed throughout the maturation period. Several quality characteristics were determined, including anthocyanin content. The objective of the experiments was to investigate which climatic determinants were most important for anthocyanin accumulation in the berries. Temperature and irradiance data, observed over time with a very thin discretization step, are called functional data in statistics. We developed the procedure SpiceFP (Sparse and Structured Procedure to Identify Combined Effects of Functional Predictors) to explain the variations of a scalar response variable (a grape berry quality variable for example) by two or three functional predictors (as temperature and irradiance) in a context of joint influence of these predictors. Particular attention was paid to the interpretability of the results. Analysis of the data using SpiceFP identified a negative impact of morning combinations of low irradiance (lower than about 100 μmol m−2 s−1 or 45 μmol m−2 s−1 depending on the advanced-delayed state of the berries) and high temperature (higher than 25oC). A slight difference associated with overnight temperature occurred between these effects identified in the morning.

The adoption of PIWI (Pilzwiderstandsfähige) grape cultivars, bred for resistance to fungal diseases, is a transformative step towards sustainable winemaking.