Quantifying the relative impact of physical and human factors on the viticultural expression of terroir

Terroir can be defined as the interaction amongst the elements that constitute a given ecosystem: climate, soil and grapevine within a given geographical location [1], and human factors, expressed as the viticultural practices [2]. Harvest yield and quality, as well as the typicality of its wines will depend on the interaction amongst these factors along with enological practices. Knowledge about the real functioning of the vineyard and designing technical schedules stand out among the advantages of the methodological approach that implies studying terroirs,.

Due to the complexity of systematic studies, research on viticulture tends to the use of reductionists approaches and to the analysis of cause-effect relationships. In contrast, the joint study of terroir key factors, such as climate, soil and cultivar, is more complex to deal with and, hence, the amount of these studies is lower.

As examples of climate influence, several authors worked on defining climatic indices to describe the suitability of a given region for producing wine [3][4][5][6] [7][8][9]. In addition, other researchers got deep into climate effects on vine functioning [10], on wine and vintage quality [11], on yield [12][13], or on a group of variables showing vine performance [14]. Grapevine energy balance when combined with its water balance regulates the group of responses to the environment (in this case, climate variables) of a given plant population [15]. Nowadays, a great number of climate analysis related to viticulture are focused on a climate change perspective, reporting a trend to increasing temperatures in many of the most prestigious grapevine growing regions worldwide [16]. This problem led to the study of vine response to increasing temperature over the growing cycle in several climatic regions [17].

Soil factor and its influence on vine performance have been comprehensively studied [2][18][19][20][21] [22] [23][24]. Several authors proved the huge influence of water availability on vintage quality [25] [26][27][28] [29][30]. Source-sink modulation through cultural practices can be considered a key factor since it affects vine vigour, yield and berry quality. Those techniques that modify source-sink relationships have been the subject of a great number of studies [31][32][33][34][35][36][37][38][39]. Pruning, shoot thinning, defoliation, shoot trimming and cluster thinning are relevant practices for regulating source-sink relationships and grapevine balance. In this sense, the operations performed by the vine grower represent an adaptation mechanism for rearranging vine components and directing the vineyard system in order to achieve a pre-defined goal.

Nevertheless, those studies including more than one determinant factor are scarce [40]. Recently, some authors [41] proved the significant effect of climate, soil and genetic (cultivar and rootstock) factors on a group of grapevine response variables. In particular, soil and climate had a greater incidence on the variability of the system than cultivar, likely due to their influence on grapevine water status.

From the results of partial studies it is possible to build models that allow for identifying the relative importance of each factor on the final response and, thus, generate tools that growers and technicians can use for a suitable management of the vineyard and improve its efficiency.

In order to answer these questions, the current study aimed to assess the relative importance of the climate, soil and source-sink relationship factors on grapevine vegetative growth, yield, berry composition and sanitary status. Secondly, the study aimed to establish the properties of each factor that exert more influence on vineyard performance.