How much does the soil, climate and viticultural practices contribute to the variability of the terroir expression?

Abstract

Context and purpose of the study ‐ When considering the application of a systemic approach to assess the intrinsic complexity of agricultural production, the following question immediately arises: how is this synthesis made? In this sense, characterizing the joint effects of environmental factors and viticultural practices on vine functioning represents a key challenge for the correct management of Terroir. In order to provide a response to this challenge, this work assesses the relative importance of the main factors comprised into the Terroir concept: climate (or “Year” effect), “Soil” and the “Source‐sink” relation, on the vegetative development, yield, berry composition and plant sanitary status.

Material and methods ‐ The study was carried out between 2011 and 2014 on six viticultural regions in the south of Uruguay, involving nine vineyards. The cultivar studied was Tannat, which was vertically trellised and north‐south oriented in all vineyards. The year effect refers to climate, which was characterized using solar irradiation and three bioclimatic indices calculated according to the Multicriteria Climatic Classification System. The soil was characterized by digging pits and determining physicochemical properties, in order to determine three textural categories and to define soil depth and water availability. The source‐sink relationship factor referred to the ratio between leaf surface and yield, and included four categories that simulated different vine balances. This factor has been assimilated to a management that winegrowers may potentially achieve through a set of technical operations, such as pruning, shoot thinning, leaf and lateral removal and cluster thinning. 
Statistical analyses included a Mixed Model with random effects to determine the relative importance of each factor on the total variability within the dataset.

Results ‐ Our results showed that vegetative growth depends mainly on the “soil” factor followed by the “Year”. Total yield per vine was explained by the “Source‐sink” relationship and the “Year*Source‐sink” interaction, both linked to the rainfall amount occurred during the maturation period. Berry weight was explained by “Year”. Rot incidence was more dependent on the “Year*Source‐sink” interaction, and then on the “Year*Soil” interaction, and on the “Soil” factor.
The synthesis of primary compounds in the berries depended mainly on the “Year” factor and the interaction of “Year*Source‐Sink”. The pH value was explained by the “Year*Soil” interaction. Secondary metabolite concentrations in the berry depended mainly on the “Source‐sink” relationship and the “Year” factor. 
This investigation enables the adjustment of technical itineraries for managing this given terroir according to the characteristics of its physical environment and the production target to be achieved.