Introduction

Vine growth, yield, and fruit composition are highly influenced by water supply from the soil. Many variations in grape and wine quality can be attributed to soil-related differences from the so-called terroir effect. Traditional understanding is that soil primarily influences terroir; however, this has been controversial in research and is now regarded to be an amalgam of soil and environmental effects (van Leeuwen and Seguin, 1994; van Leeuwen and Seguin, 2006; van Leeuwen et al., 2004; van Leeuwen, 2010). Some studies (Bader and Wahl, 1996; Noble, 1979; Wahl, 1988) found no consistent trends in sensory profiles of wine from different soil types while others (de Andres-de Prado et al., 2007) indicated that soil effects did influence chemical and sensory properties in wine. The main influence soil has on wine sensory properties seems to be due to its physical properties, water-holding capacity, and drainage characteristics. It is difficult to define the best soil in terms of texture, soil depth or mineral content as high-quality wines are grown on diverse soils worldwide. Depending on the location, it is rarely possible to relate the quality of wines in terms of soil texture, soil type or minerals (Seguin, 1983; van Leeuwen et al., 2004; van Leeuwen, 2010). In California, Noble (1979) evaluated the sensory differences of Chardonnay wines from various sites with different soil compositions. No consistent trends in wine from different soil types were observed; however, soil, must, and wine compositions varied among locations. van Leeuwen et al. (2004) studied the impact of different soil textures and grape maturation of Bordeaux cultivars in France. Gravelly soils stopped shoot growth earlier in the growing season, titratable acidity values were low, soluble solids and anthocyanins were high, and berry size was small. Sandy soils produced large berries, with low sugars and anthocyanins but high acidity. The authors also found that clay soils resulted in berries with the highest sugars, anthocyanins and phenolics, and that these soil effects were attributable to vine water status. Bader and Wahl (1996) used soils from different regions in Germany on one vineyard site to eliminate any climatic influences; they found that the soil effects on wine flavor were small and concluded that climate was more important than soil on wine sensory characteristics in a cool climate region but yield differences were found among different soil types. In another study that kept mesoclimate constant, Reynolds et al. (2007) found that there were no consistent soil texture or vine size effects on Riesling berry, must and wine composition or wine sensory attributes, but there were correlations between soil texture and composition on berry weight and potentially volatile terpene concentration. Soil effects were shown to influence chemical and sensory properties in Grenache wines from Spain (de Andres-de Prado et al., 2007). Fertile soils, with high water-holding capacity, produced wines with lower color intensity and total phenols.

The effect of soil texture therefore seems have an indirect effect in viticulture. Variation of soil characteristics such as water-holding capacity, drainage, and root penetration can have a pronounced impact on vine-to-vine variation within a vineyard. Variations in vine size and yield have been shown to be closely associated with variations in plant available water (Hall et al., 2002; Lamb et al., 2004; Cortell et al., 2005). Seguin (Seguin, 1970; Seguin, 1975) first attempted to scientifically define the terroir effect through investigating chemical properties of soils in Bordeaux and its famous chateaux. Soil chemical composition did not have a specific influence on wine quality, however the soil’s ability to regulate water supply to the vine via its physical properties was significant. Soil texture and rooting depth were noted as the most important soil factors and the best soils were those that were free draining, which avoided water logging in the rooting zone but did limit water availability later in the season. This was further supported by Asselin et al. (1983) who demonstrated relationships between soil and wine sensory profiles using soil types from different sites within the Loire Valley.

Many soil effects on vine behavior are mediated through varying water content levels and their effects on leaf water potential (ψ) or stomatal conductance (Klepper, 1968; Seguin, 1983; Seguin, 1986; van Leeuwen and Seguin, 1994; van Leeuwen and Seguin, 2006; van Leeuwen et al., 2004). Some studies indicate that plant water status is the means by which the terroir affects wine style and quality (Koundouras et al., 1999; Choné et al., 2001). In the Loire Valley, free-draining sandstone soils that provided water stress during fruit maturation were associated with intense varietal character in Cabernet franc wines (Penavayre et al., 1991). Vine water supply was noted as a major factor in the terroir effect due to its impact on accelerating budburst and increasing vine vigor (Morlat et al., 2001). van Leeuwen et al. (2004) studied soil, climate, and cultivar simultaneously and found that climate and soil had a greater impact than cultivar. They concluded that soil and climate effects were mediated through their influence on vine water status. In Ontario, low leaf ψ zones in Cabernet franc vineyards correlated spatially with anthocyanins and phenols and produced wines with more intense red and dark fruit aromas than those from high leaf ψ zones (Hakimi and Reynolds, 2010; Reynolds and Hakimi Rezaei, 2014c). Similar conclusions were reached for several Ontario Pinot noirvineyards (Ledderhof et al., 2014). Zones in a Riesling vineyard with low leaf ψ likewise produced wines with more intense citrus characteristics that were attributable to higher monoterpene concentrations in the fruit (Marciniak et al., 2013).

Vineyards have been shown to vary spatially in terms of soil, vine nutrition (Bramley, 2001; Davenport and Bramley, 2007; Reynolds and Hakimi Rezaei, 2014a), vegetative growth (Baldy et al., 1996; Bramley et al., 2011), yield, and fruit composition (Bramley, 2001; Reynolds et al., 2007; Bramley et al., 2011; Reynolds and Hakimi Rezaei, 2014b,c). Precision viticulture techniques including global positioning systems (GPS) and geographic information systems (GIS) have become powerful tools to study vineyard terroir (Reynolds et al., 2007; Reynolds and Hakimi Rezaei, 2014a–c) and variability (Bramley and Hamilton, 2004; Bramley, 2005) while keeping key environmental factors constant. Other studies that have utilized precision viticulture to explain interactions between soil characteristics and vine growth and/or fruit composition. Bramley (2001) found that soil texture had an impact on yield in Australian vineyards. Areas within the vineyard that had higher percentage of clay contained lower yielding vines. Strong spatial and temporal distribution patterns were found within vineyards for many nutrients in various tissue types of vines in Coonawarra vineyards (Davenport and Bramley, 2007).

Little research has been done to see how Niagara’s unique terroir influences wine varietal character. Some studies performed in Ontario have indicated that vine size and soil texture were spatially associated with the fruit composition and sensory characteristics of wines (Hakimi and Reynolds, 2010; Marciniak et al., 2013; Ledderhof et al., 2014; Reynolds and Hakimi Rezaei, 2014a–c), but in some cases spatial patterns in yield, vine size, and berry composition were not temporally consistent (Reynolds et al., 2007). van Leeuwen (2010) states that soil and environmental conditions that moderate vine vigor through mild water deficit stress are important for high-quality wine production and influence the terroir effect. Therefore, this study attempted to further understand the basis of the terroir effect in Ontario vineyards. The specific objectives of this research were to demonstrate the putative influences of soil texture, soil water content, and vine water status on vine and fruit development within vineyard blocks, to delineate these terroir effects using geomatic technologies, and to elucidate relationships between soil and vine water status vs. vine performance. Data on berry composition are included in a companion article (Willwerth and Reynolds, 2020) and data describing sensory differences between wines from high and low water status zones in these vineyards were published in Willwerth et al. (2018).

Materials and Methods

Results

2. Linear correlations

Correlations for each vineyard are depicted in separate Tables S1–S7. Soil variables (e.g. % sand and clay, pH, OM, CEC, BS, elements), SWC, and leaf ψ are presented as putative independent variables and vine size and yield components as dependent variables. As most soil variables are relatively stable, particularly in soils with high % clay, whereas variables such as yield components are inconsistent and subject to vicissitudes of annual weather patterns, it is not surprising that strong correlations were not abundant. Nonetheless, SWC and leaf ψ were frequently correlated to vine size and yield components.

Four vineyards were located in the eastern portion of the Niagara Peninsula (Niagara-on-the-Lake, St. Davids) and six in the western portion (St. Catharines, Jordon, Vineland, Beamsville). Among the east Niagara vineyards, at Glenlake Vineyards (GLK) the SWC was correlated with vine size in 2005 but was non-correlated in 2006 and 2007 (Table S1). Another positive correlation was soil potassium (K) vs. berry weight (2005). There were no relationships involving leaf ψ. Inverse correlations included the following: soil pH and calcium (Ca)(2007) and CEC (2005) vs. yield; soil phosphorus (P) (2005, 2006), soil K (2005) and Ca (2007) vs. cluster number; and soil Ca (2005), K (2006), and BS vs. berry weight (2005). At Château des Charmes (CDC), direct correlations included the following: SWC vs. yield (2005); leaf ψ vs. vine size (2005); SWC vs. berry weight (2007); and soil P (2005), OM (2006), and % sand (2007) vs. vine size (Table S2). Inverse correlations included the following: SWC vs. vine size (2007); leaf ψ vs. vine size (2005), yield (2006), and clusters (2007); % clay vs. vine size (2007); OM vs. yield (2005); and soil pH and Ca vs. berry weight (2006).

Among west Niagara vineyards, at PAR Vineyards, direct correlations included leaf ψ vs. berry weight (2005), and % sand and soil P vs. berry weight (2006; Table S3). Inverse correlations included the following: leaf ψ vs. clusters (2005) and berry weight (2006); soil P vs. vine size (2005); and OM (2005, 2006), soil P (2006), K (2005) and BS (2007) vs. berry weight. At HOP, no correlations were found between leaf ψ or SWC and yield in 2005 (Table S4). Positive correlations were as follows: SWC vs. yield, berry weight, and vine size (2007); and leaf ψ vs. berry weight (2007). The inverse correlation was soil P vs. yield (2006). At the Myers Vineyard (MYR), positive correlations were as follows: leaf ψ vs. vine size (2005) and berry weight (2007); SWC vs. berry weight (2006); % sand vs. vine size (2006, 2007); OM vs. vine size (2005–2007); soil pH vs. berry weight (2006); P vs. vine size (2006, 2007); Ca vs. berry weight (2006) and vine size (2005); and BS vs. berry weight (2006; Table S5). Inverse correlations included the following: SWC vs. yield, clusters and vine size (2005); % clay vs. berry weight (2006); and OM vs. yield and clusters (2005). At FLR, positive correlations were as follows: SWC vs. yield (2005); P vs. yield (2007); and Mg vs. clusters (2006; Table S6). Inverse relationships were leaf ψ vs. vine size (2005) and yield (2006); and OM vs. yield (2005). At Cave Spring Cellars (CSC), positive correlations were as follows: SWC vs. berry weight (2005); OM (2005) and P (2006) vs. yield; and P and OM vs. berry weight (2005; Table S7). Inverse correlations were SWC vs. yield and clusters (2007); and soil Mg vs. yield (2007).

Figure 1. Climate data for 2005–2007, Vineland, ON.

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Location details: 43.150° north, 79.399° west, elevation: 127 m.

Figure 2. Spatial distribution of soil texture in 2005: A, C, E, G, I, K, M, sand (%); B, D, F, H, J, L, N, clay (%).

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A,B, Glenlake Vineyard, Niagara-on-the-Lake, ON; C,D, Château des Charmes, St. Davids, ON; E,F, Paragon Vineyards, Jordan, ON; G,H, Henry of Pelham, St. Catharines, ON; I,J, Myers Vineyard, Vineland, ON; K,L, Flat Rock Cellars, Jordan, ON; M,N, Cave Spring Vineyards, Beamsville, ON. 

Figure 3. Spatial distribution of soil water content (%) and leaf water potential (1 MPa = 10 bars), Glenlake Vineyard, Niagara-on-the-Lake, ON.

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Soil water content: A, 2005; C, 2006; E, 2007. Leaf water potential: B, 2005; D, 2006; F, 2007. 

Figure 4. Spatial distribution of soil water content (%) and leaf water potential (1 MPa = 10 bars), Château des Charmes Vineyard, St. Davids, ON.

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Soil water content: A, 2005; C, 2006; E, 2007. Leaf water potential: B, 2005; D, 2006; F, 2007. 

Figure 5. Spatial distribution of soil water content (%) and leaf water potential (1 MPa = 10 bars), Myers Vineyard, Vineland, ON.

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Soil moisture: A, 2005; C, 2006; E, 2007. Leaf water potential: B, 2005; D, 2006; F, 2007. 

Figure 6. Spatial distribution of soil water content (%) and leaf water potential (1 MPa = 10 bars), Cave Spring Vineyard, Beamsville, ON.

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Soil moisture: A, 2005; C, 2006; E, 2007. Leaf water potential: B, 2005; D, 2006; F, 2007. 

Figure 7. Spatial distribution of vine size (kg), yield per vine (kg) berry weight (g), Glenlake Vineyard, Niagara-on-the-Lake, ON.

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Vine size: A, 2005; B, 2006; C, 2007. Yield per vine: D, 2005; E, 2006; F, 2007. Berry weight: G, 2005; H, 2006; I, 2007. 

Figure 8. Spatial distribution of vine size (kg), yield per vine (kg) berry weight (g), Château des Charmes Vineyard, St. Davids, ON.

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Vine size: A, 2005; B, 2006; C, 2007. Yield per vine: D, 2005; E, 2006; F, 2007. Berry weight: G, 2005; H, 2006; I, 2007. 

Figure 9. Spatial distribution of vine size (kg), yield per vine (kg) berry weight (g), Myers Vineyard, Vineland, ON.

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Vine size: A, 2005; B, 2006; C, 2007. Yield per vine: D, 2005; E, 2006; F, 2007. Berry weight: G, 2005; H, 2006; I, 2007. 

Figure 10. Spatial distribution of vine size (kg), yield per vine (kg) berry weight (g), Cave Spring Vineyard, Beamsville, ON.

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Vine size: A, 2005; B, 2006; C, 2007. Yield per vine: D, 2005; E, 2006; F, 2007. Berry weight: G, 2005; H, 2006; I, 2007. 

Discussion

1. Spatial trends and relationships within vineyard sites

1.1 Soil texture and composition

Soil texture varied in all vineyard sites (Figure 2). The degree to which they varied in terms of % sand or clay ranged was due to the geological history of the Niagara Peninsula. The soils of the region are very diverse and complex due to several historical interglacial and glacial events and are therefore quite heterogeneous (Haynes, 2000). This variation in soil is consistent with Ortega et al. (2003) who found that Chilean vineyards varied significantly in terms of chemical and physical properties. As expected, in all vineyards % sand and clay were inversely correlated. Soils higher in % sand were also higher in OM at a number of sites (e.g. CSC, FLR). Similar to the findings for texture, soil composition also varied within vineyard sites, and some vineyards were more variable than others especially in terms of soil pH, OM, and certain macronutrients, including P, K, and Ca. Within-site differences in terms of OM ranged from 0.8–1.9%. Soils higher in OM were generally found to have higher concentrations of P and K and less Ca. Differences in pH within vineyards ranged from 0.5–1.5 indicating spatial variation. Soil Ca had a positive impact on soil pH in most of vineyards. This is not surprising as calcareous soils that contain free Ca carbonate may be quite strongly alkaline. There were also strong relationships between Ca, CEC, and BS. Soil pH and BS were positively correlated but the relationship is not always linear (Wolf, 2008). Soil Mg and Ca were negatively related in most vineyards. Soil K was also negatively correlated with Mg. Soils with higher CEC have greater plant mineral nutrient-holding potential. In limestone-based soils, the Ca and Mg can out compete K in exchange sites, leading to K deficiencies in the vine due to this antagonistic effect. Some sites varied little spatially in K (GLK) whereas other vineyards had an almost six-fold difference (CDC). This was also found with K in other vineyards showing small spatial variations while others had large variations. The other macronutrients also varied spatially and to different extents. This provides justification for zone-specific nutrient management in Ontario vineyards, as some areas within sites were below adequate levels for grapevine nutritional requirements, where other regions were more than adequate (Ontario Ministry of Agriculture Food and Rural Affairs, 2007). In some vineyards, low vine size was found in K-deficient zones. Cellular K is crucial in plant biochemical processes, including carbohydrate production, protein synthesis, solute transport, and maintenance of plant water status. Lack of K reduces shoot growth, vine vigor, berry set and crop yields (Keller, 2016).

Figure 11. Principal components analysis of viticulture and soil variables, 2005–2007.

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A–C: Glenlake Vineyards. D–F: Château des Charmes. G-I: Myers Vineyard. J–L: Cave Spring Vineyard.

While individual vineyards exhibited wide spatial variation for many soil composition variables, no clear trends were found on their putative impact on vine performance or yield. No consistent relationships were observed for any soil variable on vine performance over three vintages for any vineyard. While Ca and P had an influence on vine size in a few vineyards and vintages, OM and texture were found on more occasions but not consistently. The same observation was found with the impact of these soil factors on yield components such as berry weight and yield/vine. The exception was that if the area zone of a vineyard displayed low concentrations of certain macronutrients then vine size and yield suffered in those instances. Petiole analysis indicating the nutrient status of the vine would perhaps have given clearer explanation of the impact of soil composition on vine performance or yield components but others have indicated that it is difficult to make implications about the impact of nutrients on the terroir effect (Reynolds and de Savigny, 2016; Reynolds et al., 2007). Therefore, although vineyards varied in terms of soil composition, no obvious deficiencies were present, hence there was no clear impact of soil composition on vine performance or yield components.

In general, soil texture was related to SWC, and areas of higher % clay had higher SWC as expected. For the most part, these areas often had vines of higher leaf ψ but there may have been other interactive factors that possibly influenced vine water status other than just soil texture. Some inconsistencies between the different vineyards studied may have been the result of differences in rooting depth, soil depth (Table 1), and gravel content as seen through soil pits (no data available) or differences in drainage. Therefore, these factors cannot be ignored when looking at relationships between soil and vine water status.

1.2 Soil and vine water status

The values of SWC varied based on the climatic conditions experience throughout each of the three growing seasons. As the sites were non-irrigated, the percentage of moisture in the soil can be attributed to rainfall and the physical properties of the soil. SWC values within sites were highest in 2006 followed by 2007 and were lowest in 2005. These trends were similar in terms of leaf ψ, which varied within all the vineyards studied. Leaf ψ was lowest in 2005 and highest in 2006. In white wine cultivars, leaf ψ values < -1.0 MPa are normally indicative of mild-to-moderate water stress, whereas values < -1.2 MPa might indicate more severe stress (van Leeuwen 2010). In each vintage there were areas within vineyards that had ψ values < -1.0 MPa, indicating some water stress evident (van Leeuwen, 2010). In every vineyard studied, consistent areas of differing leaf ψ values could be identified, and therefore distinct regions were delineated that could be categorized as “high” and “low” water status. This is consistent with Acevedo-Opazo et al. (2008) who found that it was possible to assess spatial variability of vine water status within vineyards, even those small in size (<1 ha). In many cases, particularly in the hot and dry 2005 and 2007 vintages, the “low” water status regions consisted of vines experiencing moderate to high water stress (< -1.2 MPa). SWC varied spatially within all vineyard sites examined. Spatial trends within vineyards for vine leaf ψ were temporally stable over a 3-year period for eight vineyards. Spatial trends in SWC were found not to be as temporally stable as ψ but were still evident in many areas of these eight vineyards. Variation in SWC was site-specific and was not only due to annual rainfall but also evaporation, water-holding capacity, differences in the effective root zone and drainage unique to each site (Table 1). Furthermore, some of the inconsistencies from year to year in terms of SWC could possibly be related to variables such as human disturbances of the soil (i.e. tilling, grape hoeing) leading to poor instrument contact with the soil.

Conclusions

Vineyards within the Niagara Peninsula were variable in terms of soil texture, composition, nutrition, and moisture. Furthermore, many viticulture variables such as leaf ψ, vine size, berry weight, and yield were spatially variable, and as hypothesized, consistent leaf ψ zones were identified within vineyards in three distinct vintages. Many geospatial patterns and relationships were determined and were temporally stable, and this temporal stability in these variables occurred despite different growing seasons. Generally, the strongest relationships were those concerning leaf ψ, SWC, vine size, and berry weight. No consistent relationships were found concerning soil composition. The most consistent soil variables that impacted vine performance and yield components were physical properties, particularly texture when sand content was high. Therefore, soil had some indirect effects, but leaf ψ was more likely a major contributor to the terroir effect, as it had a major impact on vine size, berry weight and yield in many vineyards across multiple vintages. Temporal stability is required for many practical geomatic applications to be initiated in Niagara vineyards, but it is also of importance to future research endeavors for this project as well as others.

Acknowledgments

Our thanks are extended to the Natural Sciences and Engineering Research Council of Canada and the Wine Council of Ontario for research funding for research funding. Thank you to all of the industry partners for allowing this research to be possible. These include Glenlake Orchards and Vineyards, Château des Charmes, Cave Spring Cellars, Henry of Pelham Family Estate Winery, Reif Estate Winery, Flat Rock Cellars, Lambert Farms, Bill and Caroline Myers, Paragon Vineyards, Vailmont Vineyards. Our thanks are also extended to Ker Crop Management Services (KCMS) for their assistance with GPS data.

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