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Terroir Influence on Water Status and Nitrogen Status of non-Irrigated ( vinifera). Vegetative Development, Must and Composition (Example of a Medoc Top Estate , Saint Julien Area, Bordeaux, 1997) X. Chone1-2, C. Van Leeuwen1'2, P. Chery2 and P. Ribereau-Gayon1 1) Faculte d'Oenologie de Bordeaux, Universite Bordeaux 2 Victor Segalen, 351 Crs de la Liberation, 33405 Talence Cedex, France 2) ENITA de Bordeaux, 1 Crs du General de Gaulle, 33175 Gradignan Cedex, France Submitted for publication: March 2000 Accepted for publication: January 2001 Key words: , Nitrogen, water status, , Cabernet Sauvignon, vigour, , phenolic content, must nitrogen content, leaf water potential

Terroir effect on vine vigour, must composition and wine quality was investigated for Cabernet Sauvignon during a rainy in a top estate of the Medoc area (Bordeaux, France). Soil was the only variable in this survey. Vine water status was determined by means of leaf water potential. Mild water deficits were observed only on a gravelly soil with a shallow root zone. Vine nitrogen status was determined by total must nitrogen content. Nitrogen status varied from deficient to unlimited. Nitrogen deficiency reduced vine vigour to a greater extent than did mild water deficits. The smallest berries, as well as the highest phenolic content for both must and wine, were observed under nitrogen deficiency. Both early mild water deficits and a nitrogen deficiency throughout the growth period were demonstrated to have beneficial effects on the phenolic content of berries and on wine quality. Two combinations of vine water status and vine nitrogen status led to the most highly appreciated : a low nitrogen status without water deficits and a medium nitrogen status accompanied by mild water deficits.

For any given vineyard terroir can be described as the combina- and Cook, 1971; Spayd et al, 1994) that nitrogen fertilisation tion of pedoclimatic conditions, vine components such as culti- increases vigour. var, clone and as well as viticultural techniques (prun- In the Bordeaux oceanic climate rainfall can vary to a consid- ing system, management, etc.). Given this, terroir must be erable extent from one season to another. In a dry season, such as seen as a complex system with multiple variables: it is impossi- 1990, high enological potential and therefore wine quality ble to study all the variables in one experiment. Within a single are strongly linked to mild water deficits (Van Leeuwen and estate (10 to 100 ha) in Bordeaux, there is generally no climatic Seguin, 1994). In a rainy season, this is less likely to occur even variation but several types of soil. It is well known that the effect though a soil effect on wine quality is generally admitted to exist of the soil on vine behaviour is mediated through varying water- despite the rainy conditions. As a better understanding of the ter- content levels and their effects on vine water status (Seguin, roir effect can help growers in their vineyard management and 1970; Seguin, 1986; Van Leeuwen & Seguin, 1994). Water selection, the effect of soil variation on vine vigour, berry deficits occur when transpiration exceeds the ability of the root constitution and wine quality was investigated in this survey dur- system to supply water to the transpiring leaves. Mild water ing a rainy vintage. Vine water status and vine nitrogen status deficits are known to have positive effects on reducing berry size were measured by means of physiological indicators. In the case (Smart, 1974) and on berry skin anthocyanin and tannin content studied soil was the only variable differentiating blocks planted in red grape varieties (Matthews & Anderson, 1988; Van with the same cultivar and rootstock and with the same vine spac- Leeuwen & Seguin, 1994; Koundouras et al, 1999). Schultz and ing and subject to the same canopy management. Conradie Matthews (1993) observed that in potted vines water deficits (1986) demonstrated that vine nitrogen uptake from bud break caused embolism in the xylem shoot apex, which stopped shoot through fruit maturity is progressively less utilised for vegetative growth. This has been confirmed in field studies (Matthews et al, growth and increasingly more utilised by the fruit. This was con- 1987; Van Leeuwen & Seguin, 1994; Naor & Wample, 1996). firmed by Soyer et al (1995), who showed that vine berry nitro- Given this consideration, it can be said that under mild water gen content closely reflected mineral nitrogen availability in the deficits vegetative growth is no longer in competition with repro- soil. Thus, berry total nitrogen content can be used as a physio- ductive development as a sink of resources. Hence logical indicator of vine nitrogen status. However, the levels of fruits are primary sinks. This can partly explain the richer must total nitrogen berry content as an indicator of vine nitrogen status and wine constitution obtained from vines having undergone mild is poorly documented. water deficits. MATERIALS AND METHODS Without the addition of nitrogen fertiliser, vine nitrogen status depends upon soil organic matter content, its mineralisation rate Experimental location and plant material and the C/N ratio. It has been shown for (Delas et al, The study was conducted in Leoville Las Cases vineyard. Saint- 1991) and for Thompson seedless and White (Kliewer Julien, Haut-Medoc, Bordeaux area, France. Soil mapping of this

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 Terroir Influence on Waier and Nitrogen Status of Cabernet Sauvignon vineyard revealed an unexpected soil variation: nine pedological were immediately counted and weighed to determine average types spread over only 100 ha. Four blocks planted with Vitis fresh berry mass. Berries were pressed and the juice was gently vinifera cv. Cabernet Sauvignon grafted on Vitis riparia L. root- centrifuged to remove suspended solids. content was mea- stock were studied. Vine age was between 24 and 31 years. The sured by refractometry. Titratable acidity was measured manual- four blocks were identified as 1G, 3 A, 4H and 5P. Each block was ly with Bromothymol blue. The titration was done with 0.1 N set up on a different soil type. To avoid soil variation inside a NaOH to an end point of pH 7.0. was determined block, only 100 vines were studied per site, all located around the using an enzymatic kit from Boehringer Mannheim. soil pit studied. The soil type, texture, percentage of organic mat- On 200 berries were determined by the method of ter in fine soil, occurrence of water table and root zone depth are Ribereau-Gayon & Stonestreet (1965). The measurement of presented in Table 1. absorbency was conducted at a wavelength of 520 nm (optical The four blocks were less than 500 m apart. The altitude of the distance: 1 cm). Tannins were measured by the 1PT: "indice des four blocks varied from 10 to 20 m and row orientation was iden- polyphenols totaux" (Ribereau-Gayon, 1970). The wavelength tical. Hence it was accepted that no climatic variation occurred used was 280 nm (optical distance: 1 cm). among the four blocks. This was confirmed by the vine phenolo- Micro vinifi cation gy in 1997, which was similar for all the studied (bloom: Microvinification was conducted identically for all lots. For every May 25; veraison: July 21). The vines were spaced 1 x 1.1 m terroir 50 kg of fruit were harvested on the same day (September apart and double Guyot pruned; trunk height was 0,4 m from the 27). The fruit from each block was crushed and stems were soil surface. During vegetative development, vine canopy was removed. For every lot 40 kg were put into a SOL stainless steel mechanically cut at 1.1 m height for every block. tank. In order to have similar wine alcohol content for tasting, 1G, Water potentials 3A and 5P must were chaptalised to obtain the same sugar con- Pre-dawn leaf water potential (dawn^) and leaf water potential tent as found in 4H. Alcoholic fermentation and malolactic fer- (leaTf) were measured with a pressure chamber (Scholander et mentation were enhanced with a selected yeast strain and a select- al, 1965) equipped with a digital manometer (SAM Precis 2000, ed bacteria strain, respectively. All the wine-making parameters 33175 Gradignan, France). DawnY was measured at the end of (fermentation arrd maceration temperature, pumping over fre- the night on uncovered mature leaves. LeaPf was measured on quency, draining away, etc.) were similar. mature leaves exposed to sunlight, whether they were transpiring or not (Turner, 1981). Wines were tasted blindly by a panel of 15 professional tasters. Nitrogen status They were noted by positive preference order from 1 to 4. The As in the preceding years, no nitrogen fertiliser was added in scores of all judges for a wine were summed. Least significant 1997. Hence vine nitrogen uptake resulted mainly from mineral- difference (LSD) was determined by a modified Chi2. isation of organic matter. Vine nitrogen uptake was estimated Statistics weekly, from veraison through , by the berry total nitrogen Water potential and vigour indicators data were analysed with the content (Bell et al, 1979). ANOVA procedure and the Newman Keuls test to determine least Vine vigour significant difference (Statbox Pro Software). Dry leaf mass was measured on eight vines per terroir just before RESULTS harvest. Leaf area per vine was deduced from the correlation Water status obtained. Average total bunch mass per vine was measured on 30 vines per block on the day of harvest. Average pruning mass per Soil water content was at a field capacity on all the soils studied in the spring (April), which is usual in the French oceanic area. In vine was determined on 25 vines per block. the Medoc 1997 was a rainy vintage: the rainfall in May, June and Must characteristics from veraison through harvest August was far above the average calculated over a 39-year span. From veraison through harvest one thousand berries were sam- Conversely, rainfall was a bit less than average in July and pled weekly at random from 100 vines on each site. These berries September (Table 2). From bloom through veraison total rainfall

TABLE 1 Soil and rooting characteristics of the studied plots.

1G 3A 4H 5P

Type of soil Neoluvisol on Planosol sedimorphe with Redoxisol with heavy Podzosols gravely soil heavy clay subsoil clay subsoil Gravel content 75% 15% 50% 15% Water table no no yes no Texture of fine soil in limits of root zone depth Sandy clay Heavy clay Sandy clay Sandy Organic matter (% in fine soil) in the top 60 cm 1.5 1.2 0.5 2 Root zone depth (meter) 1 1.5 0.7 2

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 20 lerroir influence on Water and Nitrogen Status oj l^atternel bauvignon

TABLE 2 low root zone, no water deficits were detected. This was due to a Monthly rainfall in Saint Julien in 1997, compared with the long- permanent water table linked to the subsoil clay depression. term average. Conversely, on 3A the subsoil clay is convex. Thus no water table can be formed ant the root zone is deeper (Table 1). May June July August September Nitrogen status

Rainfall From veraison through harvest, berry total nitrogen content for 1997 (mm) 158.4 146.6 36 80 32.2 4H was threefold lower than for 5P and twofold lower than for IG Average rainfall (Fig. 3). Berry total nitrogen content of 3A was between that of 1961-1990 (mm) 77.3 56.2 46.5 54.2 74.1 4H and of IG. Throughout this period the difference between berry total nitrogen content appeared to remain constant from one was 18 mm and from veraison to harvest 113 mm. From July block to another. through September 1997 5P dawnT data varied from -0.10 to - Lower total nitrogen content for 4H reflected the low organic 0.17 MPa, whereas over the same period IG dawn¥ data varied matter content in this soil (Table 1). Conversely, 5P soil organic from -0.12 to -0.30 MPa (Fig. 1). At three different stages (July, matter percentage was fourfold higher than for 4H, with total August and September), dawn*F data were significantly lower for berry nitrogen being threefold higher than for 4H. Thus, under the IG than for the other blocks. conditions of this survey, berry total nitrogen content appeared to reflect soil organic matter content closely. On August 23 midday leaf water potential showed no differ- ences among the 4 soils (Fig. 2). Yet IG leaf water potential was Vine vigour significantly more negative than that of the other locations at the A strong correlation between leaf area (measured with a planime- end of the afternoon, being the beginning of the recovery period ter) and dry leaf mass was established. Total leaf area per vine of vine water status. This confirmed the lower pre-dawn leaf (Table 3) was not significantly different for IG, 3A and 4H, indi- water potential measured on IG during the same period. Climatic cating that total leaf area per vine was not affected by water sta- conditions were identical for the four blocks studied. Thus water tus for these 3 blocks. Hence, IG mild water deficits were only status differences observed in 1997 reflected mostly soil ability to due to low soil-water content available in the root zone depth. supply water to the vine. Hardie & Considine (1976) and Van Moreover, significantly larger total leaf area per vine did not Leeuwen et al (1994), showed that dawnY of -0.30 MPa reflect- enhance water deficits on 5P. This confirmed the higher soil- ed a mild water deficit, which induced slackening of shoot water content in the root zone depth of 5P. growth. Given this, IG can be considered as the only block where The significantly lower total leaf area per vine for 4H, in com- vines underwent mild water deficits in 1997. parison to 5P was not due to water status, which was similar for As IG received as much rainfall as 5P, where no water deficit both terroirs. The lower vine nitrogen status on 4H appeared to occurred, IG water deficits reflected low water-storage capacity, explain its weaker vigour. Furthermore, the total pruning mass due to a high proportion of gravel in the shallow root zone (Table per vine and the total cluster mass per vine were also significant- 1). Conversely, on 5P the root zone was twofold deeper than on ly lower on 4H than on 5P. IG, whereas the gravel content in the root zone was fivefold As with total leaf area per vine, 4H and IG showed no signifi- lower. These conditions were reflected in the high dawnT data cant difference for total pruning mass per vine, nor for total leaf collected from July to September on 5P. On 4H, despite the shal- area per vine. Two vigour indicators, total bunch mass per vine

-0,2--

(0 -0,25 Q)

-0,35 JULY AUGUST SEPTEMBER FIGURE 1 Dawn leaf water potential evolution from July through September 1997, Data are means of 8 measurements on 8 adjacent vines. Error bars indicate SE.

S. Afr. J. EnoL Vitic., Vol. 22, No. 1, 2001 Termir Influence an Water and Nitrogen Status of Cabeme! Saavignon II

0,0

d) « -1,0

-o~ 1G leaf water potential -•- 3A leaf water potential -D-4H leaf water potential -*c— 5P leaf water potential

-1,6 02:24 03:36 04:48 06:00 07:12 08:24 09:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 FIGURE 2 Diurnal leaf water potential on August 23, 1997. Data are means of 8 measure- ments on 8 adjacent vines. Error bars indicate SE.

360 - •

330-•

300--

270 -- j"

f 240-

210--

180--

150--

120 -

90-- SEPTEMBER FIGURES Berry total nitrogen content from veraison through harvest (1997).

TABLE 3 status, seemed to have had more influence on vigour than did vari Vigour indicators: Total leaf area, total pruning mass and total ations in water status between 1G and 4H or between 1G and 3A bunch mass per vine. Total leaf area per vine and total pruning mass per vine for 51 1G 3A 4H 5P were significantly higher than for the 3 other terroirs, while 51 total cluster mass was significantly higher than 4H only. As tht Total leaf area per trellising and pruning system were the same on the four sites, thii 1 vine (m2) 1.01 a' ) 0.96 a 0.8 a 1.46 a showed that low nitrogen status on 4H reduced total bunch mas: Total pruning mass per vine to a greater extent than did the mild water deficits on 1G per vine (kg) 0.24 a b 0.31 b 0,19 a 0.43 c This further emphasised that low vine nitrogen status had ; Total bunch mass per vine (kg) 0.935 a b 1.09b 0.765 a 1.103b greater influence on vigour than did mild water deficits befort veraison. (') Values within rows followed by the same letter do not differ significantly. Fresh berry mass From veraison through harvest 5P fresh berry mass was constant and total shoot mass per vine, showed that 3A was significantly ly 30% higher than that of 4H, whereas it was only 10% to 15 9i more vigorous than 4H, but no more than 1G. Thus the difference higher than that of 1G and 3A (Fig. 4). Fresh berry mass and tota in nitrogen supply between 3A and 4H, which had the same water cluster mass per vine showed a strong linear correlation (R2=0.92

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 12 Terroir Influence on Water and Nitrogen Slalus of Cabeme! Sauvignon

160

150

3A 140 -1G -4H -5P

70 -•

60 AUGUST SEPTEMBER FIGURE 4 Fresh berry mass evolution from veraison through harvest (1997).

230 y-

220 -• 210--

200 -• 190 --

180 -• 170 --

160 -

150 -•

140-•

130 -• 120-•

110-- 100 --

90-

AUGUST SEPTEMBER FIGURES Must-reducing sugar content evolution from veraison through harvest (1997).

440,0

•3- Q>

JULY AUGUST SEPTEMBER FIGURE 6 Must titrable acidity evolution from veraison through harvest (1997).

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 Terroir Influence on Water and Nitrogen Status of Cabernet Sauvignon 13

SEPTEMBER

FIGURE? Must malic acid (meq/L) content evolution from two weeks post-veraison through harvest (1997).

1400

1300-

— 1200 - 3A

1 G 1 "'

C

700 --

600-•

500

400 AUGUST SEPTEMBER FIGURES Must anthocyanin content evolution from two weeks after veraison through harvest (1997). n=4), which demonstrated that flower abortion did not explain the acid content. For the four sites a strong linear correlation difference between the sites. (R2=0.97; n=4) between average dawn*JK data (from July through September) and berry malic acid content at the harvest was Low fresh berry mass on 4H confirmed the low vigour previ- observed. ously observed. Lower fresh berry mass on 1G and 3 A, compared to 5P, can be attributed to mild water deficits and lower nitrogen Anthocyanins, tannins and wine appreciation status respectively, even though these are not reflected by signif- Anthocyanin content for 4H was almost twofold higher than for 3A icant differences in total cluster mass per vine. and 5P, whereas the difference between 4H and 1G was less pro- Berry composition through ripening nounced (Fig. 8). IPT differences followed the same hierarchy, with 4H and 1G exhibiting the highest tannin content (Table 4). Must from 4H and 1G exhibited the highest sugar content and the The professional panel of tasters distinguished 4H and 1G as the lowest acidity, whereas the reverse was true on 5P (Figs. 5, 6 and best wines (Table 4). The most appreciated wines were also the 7). Must sugar content was less for 1G than for 4H. Even though highest in phenolic content. Wine phenolic content correlated titratable acidity on 1G and 4H was similar, malic acid content closely with phenolic content (Table 4). Must phenolic content for was nevertheless lower on 1G. As already shown by Van Leeuwen 3A, 4H and 5P suggested that low nitrogen status without water and Seguin (1994), vine water deficits enhance low must malic deficits was linked to high enological potential for a red grape vari-

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 TABLE 4 Conradie (1980, 1986) demonstrated that most of the vine nitro- Must phenolic content at the harvest, wine phenolic content and gen uptake occurs from bud burst through veraison. During this wine-tasting appreciation. period nitrogen is increasingly allocated to fruit. From veraison through harvest Conradie (1991) observed a translocation on 1G 3A 4H 5P of nitrogen from shoot, leaves and permanent struc- ture to bunches. These observations were confirmed by constant or Must anthocyanin content slightly increasing must total nitrogen content on the 4 sites in 1997, at harvest (mg/L) 823 1180 748 Must tannin content at from veraison through harvest, despite different rates of berry diam- harvest (IPT)(1) 33 29.8 36.5 eter increase (Figs. 3 and 4). Low nitrogen status for 4h can thus be Wine anthoeyanin considered as reflecting limited vine nitrogen uptake since bud content (mg/L) 611 463 730 401 break. This could explain why the low nitrogen status of 4H reduced Wine tannin content (IPT) 54 50 70 43 vigour more than did 1G mild water deficits for 1G. 4H low nitro- Wine-tasting sum rate 50.5a(2) 39 b 58 a 21 c gen status was constant through the vegetative and the reproductive periods (Fig. 3), whereas 1G mild water deficits appeared at the end (i) IPT = "indice des polyphenols totaux". of fruit set and were not permanent until harvest (Fig. 1). <2> Values within rows followed by the same letter do not differ significantly. Further investigations will be necessary to define more accu- rately the range of total nitrogen content in must leading to the ety such as Cabernet Sauvignon. This confirmed the result of best must and wine quality. Different total nitrogen contents data Keller and Hrazdina (1998) on continuously irrigated, potted on 1G and 4H indicated that a nitrogen status varying from low Cabernet Sauvignon. They observed that excessive nitrogen fertili- to medium favoured the production of highly appreciated wine in sation decreased win phenolic content. In a rootstock trial Delas et this Bordeaux top estate. Yet 1G and 3A grape total nitrogen con- al. (1991) observed an increase of phenolic grape content for some tent data suggested that a medium nitrogen status was adequate to of the where nitrogen fertilisation was not applied. obtain a high-quality wine, if associated with mild vine water Hence, both early mild water deficits and lower nitrogen status deficits. Conversely, under the conditions of this survey, without throughout the growth period had beneficial effects on total berry vine water deficits only nitrogen deficiency on 4H (90 to 150 phenolic contents and wine quality. This appeared to be linked to mg/L of total must nitrogen) had an obvious positive effect on the limiting effect on the vine vigour of both of these factors. must and wine phenolic content. This positive effect on wine DISCUSSION quality suggested that nitrogen deficiency should be maintained in the vineyard and that nitrogen deficiency in must should be With the same water status for both sites, lower nitrogen status on corrected in the tank before and/or during the fermentation 4H than on 5P induced a decrease in vigour. The total leaf area process. This practice is already followed with success in several per vine, the total pruning shoot mass per vine and the total clus- Bordeaux vineyard areas. ter mass per vine were respectively 55%, 44% and 30% lower on 4H than on 5P. Considering these vigour indicators, 4H under- CONCLUSIONS went a clear nitrogen deficiency in 1997. The total cluster mass This terroir survey, carried out during a rainy season in the per vine represented a calculated yield of 6.5 tons per ha for 4H, Bordeaux area, revealed a soil effect on vine nitrogen status mea- suggesting that nitrogen deficiency level was moderate, as it sured by must total nitrogen content. Despite the rainy vintage, we allowed an acceptable yield for a high-quality wine-producing observed on a gravelly soil (1G) mild water deficits linked to low vineyard. soil water content in the shallow root zone. Low nitrogen status Bell et al (1979) reported on continuously irrigated Thompson was found on soil having a particularly low organic matter content seedless that for a total nitrogen content of must at harvest rang- (4H). We observed that low nitrogen status reduced vine vigour ing from 287 to 754 mg/L no significant difference occurred in more than did mild water deficits. Yet when vines were subject to crop mass per vine. Kliewer and Cook (1971) showed on potted one of these limiting factors, the wines produced in this Bordeaux vines that leaf area and trunk circumference increased linearly top estate were of significantly higher quality. Low vine nitrogen with increasing concentrations of nutrient solutions ranging from status induced high berry tannin and anthocyanin content, accom- 0 to 4 mM of NOs, whereas they remained constant with concen- panied by low berry mass. It also reduced yield, but this may be trations ranging from 4 to 8 mM of NOs. This suggests that the acceptable in a very high-quality grape-producing vineyard. Bell et al (1979) range of must total nitrogen content indicated no Considering the benefits of low vine nitrogen status on the phe- lack of nitrogen, because it was superior to the threshold value nolic content of must and wine, it remains to define how this low where nitrogen begins to have an effect on vigour. In 1997 5P nitrogen status can be managed more accurately in order to con- must total nitrogen content (290 to 370 mg/L from veraison serve the equilibrium between the highest possible wine quality through harvest) fell within this range. Given this, 5P must total and a decreased but economically acceptable yield. nitrogen data reflected no limiting vine nitrogen status. Moreover, 3A must total nitrogen content (185 to 230 mg/L) corresponded LITERATURE CITED to an intermediate level of vine nitrogen status, between those of 5P and of 4H. This was emphasised by the fact that 3A vigour, Bell, A.A., Ough, C.S. & Kliewer, W.M., 1979. Effects on must and wine compo- sition, rates of fermentation and wine quality of nitrogen fertilisation of Vitis estimated by the total pruning mass per vine and the total cluster vinifera var. Thompson seedless grapevines. Am. L Enol. Vitic. 30, 124-129. mass per vine, was significantly lower than that of 5P and signif- Conradie, W.J., 1980. Seasonal uptake of nutrients by Chenin blanc in sand cul- icantly higher than that of 4H, with no water status difference. ture: I. Nitrogen. S. Aft. J. Enol. Vitic. 2, 59-65.

S. Afr. J. Enol. Vitic., Vol. 22, No. 1,2001 Terroir Influence an Water and Nitrogen Status of Cabemet Sauvignan 15

Conradie, W.J., 1986. Utilisation of nitrogen by the grapevine as affected by time Ribereau, P. & Stonestreet, E,, 1965, Le dosage des anthocyanes dans le vin rouge. of application and soil type. S. Afr. J. Enol. Vitic. 2, 76-82. Bull. Soc. Chim. 9, 2649-2652.

Conradie, W.J., 1991. Distribution and translocation of nitrogen absorbed during Scholander, RE, Hammel, H.J., Bradstreet, E.D. & Hemmingsen, E.A., 1965. Sap early summer by two-year-old grapevines grown in sand culture. Am. J. Enol. pressure in vascular plants. Science 148, 339-346. Vitic. 42, 180-190. Delas, J. Molot, C. & Soyer, J.P., 1991. Effects of nitrogen fertilisation and graft- Schultz, H.R. & Matthews, M.A., 1993. Xylem development and hydraulic con- ing on the yield and quality of the crop of Vitis vinifera cv. Merlot. Proceedings ductance in sun and shade shoots of grapevine (Vitis vinifera L.), evidence that low light uncouples water transport capacity from leaf area. Planta 190, 393—406. of the International symposium on nitrogen in and wine, Seattle, pubbshed by The American Society for Enology and . 242-248. Seguin, G,, 1970. Les sols des vignobles du Haut-Medoc. Influence sur 1'alimen- Hardie, W.J. & Considitie, J.A., 1976. Response of grapes to water deficit stress tation en eau de la vigne et sur la maturation du raisin. These de doctoral d'etat, in particular stages of development. Am, J. Enol, Vitic. 2, 55-61. Faculte des Sciences, Universite de Bordeaux.

Keller, M. & Hrazdina, G., 1998. Interaction of nitrogen availability during bloom Seguin, G., 1986. "Terroirs" and pedology of wine growing. Experientia 42, and light intensity during veraison. II. Effects on anthocyanin and phenolic devel- 861-873. opment during grape ripening. Am. J. Enol. Vitic. 49, 341-349. Smart, R.L., 1974. Grapevine response to furrow and trickle irrigation. Am. J. Kliewer, W.M. & Cook, J.A., 1971. Arginine and total free amino acids as indica- Enol. Vitic. 25, 62-66. tors of the nitrogen status of grapevines. Am. J. Enol. Vide. 96, 581-587. Koundouras, S., van Leeuwen, C., Seguin, G. & Glories, Y., 1999. Influence of Soyer, J.P., Molot, C., Bertrand, A., Gazeau, O., Lovelle, B.R. & Delas, J., 1996. water status on vine vegetative growth, berry ripening and wine characteristics in Influence de I'enherbement sur 1'alimentation azotee de la vigne et sur la compo- e Mediterranean zone (example of Nemea, Greece, variety Saint George, 1997), J. sition des moflts et des vins. In: Oenologie 95, Actes 5 Symp. Inter. Oenologie, Inter. Vigne Vin. 33, 149-160. Bordeaux. Tec Doc ed., Paris. 81-84. Matthews, M.A., Anderson, M.M. & Schultz, H.R., 1987. Phenologic and growth Spayd, S.E., Wample, R., Evans, R.G., Stevens, R.G., Seymour, B.J. &Nagel, responses to early and late season water deficit in . Vitis 26, C.W., 1994. Nitrogen fertilisation of white Riesling grapes in Washington. Must 147-160. and wine composition. Am. J. Enol. Vitic. 45, 31-41.

Matthews, M.A. & Anderson, M.M., 1988. Fruit ripening in Vitis vinifera L.: Turner, N.C., 1981. Techniques and experimental approaches for the measurement Responses to seasonal water deficits. Am. J. Enol. Vitic, 39, 313-320. of plant water status. Plant Soil 58, 339-336. Naor, A. & Wample, R.L., 1996. Diurnal internode growth rate in field-grown 'Concord' (Vitis labrusca) grapevines. J. Hortic. Sci. 71, 167-171, Van Leeuwen, C. & Seguin, G., 1994. Incidences de I'alimentation en eau de la vigne, appreciee par 1'etat hydrique du feuillage, sur le developpement de 1'ap- Ribereau-Gayon, P., 1970. Le dosage des composes phenoliques totaux dans les pareil vegetatif et la maturation du raisin (Vitis vinifera L. cv. Cabernet franc, vins rouges. Chim. Anal. 52, 627-631. Saint Emilion, 1990). J. Inter. Vigne Vin. 28,'81-100.

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 Relationship Between Microclimatic Data, Aroma Component Concentrations and Wine Quality Parameters in the Prediction of Wine Quality J. Marais1, F. Calitz2 and P. D. Haasbroek3 1) ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa 2) ARC Biometry Unit, Private Bag X5013, 7599 Stellenbosch, South Africa 3) ARC Agromet, Private Bag X5013, 7599 Stellenbosch, South Africa Submitted for publication: September 2000 Accepted for publication: April 2001 Key words: , temperature, radiation, Sauvignon blanc quality, prediction model

Sauvignon blanc grape chemical and wine sensory data, as well as meteorological data (temperature and visible light radiation), collected in three climatically different wine regions in South Africa over three seasons and from two different canopy treatments were statistically analysed. A model for the prediction and/or definition of Sauvignon blanc wine quality was developed. The model utilises above- and within-canopy radiation and can explain 68.8% of the variation in the cultivar-typical vegetative/asparagus/green pepper intensity of Sauvignon blanc wine. Other significant correlations, e.g. between temperature and monoterpene concentrations, were also obtained. Further research is necessary to test and refine this model for application under different environmental conditions.

Over many years research has been aimed at developing a simple The purpose of this study was to correlate microclimatic data model or recipe that could define and predict wine quality. (temperature and radiation) with aroma component concentra- Examples are sugar/acid ratio (°B/TTA) (Du Plessis & Van tions and wine quality parameters of Sauvignon blanc and to Rooyen, 1982), the glycosyl- (G-G) assay (Francis et al, develop a model for predicting wine quality. 1998) and the colour index (Holgate, 2000). Such a MATERIALS AND METHODS model should also be useful as a method to compensate the grape Grapes, regions and seasons producer according to grape quality. The aim further is that the model should incorporate parameters that are easily measurable Vitis vinifera L. cv. Sauvignon blanc grapes, grown in three cli- under field conditions, instead of parameters such as aroma matically different regions, namely Robertson (Region IV, 1945 - impact volatiles, the quantification of which is dependent on 2222 degree days), Stellenbosch (Region IE, 1668 -1944 degree complicated and expensive gas chromatographic and mass spec- days ) and Elgin (Region II, 1389 - 1667 degree days) (Le Roux, trometric analyses. Due to the complexity of factors affecting 1974), were used. A single canopy manipulation treatment, which grape and wine composition and quality, attempts to date have altered microclimate in a natural way to obtain a higher degree of achieved varying degrees of success and a foolproof, simple shading, was applied in each region (Archer & Strauss, 1989; model still has to be developed. Nevertheless-, earlier attempts Marais, Hunter & Haasbroek, 1999). Control vines were not were valuable and all contribute something to the eventual solu- manipulated. Three replications, consisting of 15 vines per repli- tion of this problem. ca, were used. The general viticultural practices followed were described by Marais et al. (1999). Grapes were obtained over Significant correlations between microclimatic parameters and three seasons, namely 1997, 1998 and 1999. Results of the 1997 wine sensory characteristics were reported earlier (Noble, Elliot- and 1998 seasons were published by Marais et al. (1999) and tri- Fisk & Alien, 1995). Models using light radiation in the predic- als during the 1999 season were a repetition of the first two sea- tion of photosynthesis under field conditions, were also devel- sons. oped (Blackburn & Proctor, 1983; Goudriaan, 1986; Spitters, Grape samples (whole bunches, 2kg per sample) were collect- 1986; Haasbroek, Myburgh & Hunter, 1997). Photosynthesis is ed weekly at random from each treatment and replicate over three dependent on light radiation and temperature and is indirectly an weeks between approximately 16°B (close to veraison) and 21°B important factor in grape composition development. (ripeness). Grapes were harvested at ripeness (fourth ripening stage) for wine production, following standard Nietvoorbij prac- The approach in this study was to investigate the possible use tices for small-scale production (Marais et al., 1999). of microclimatic parameters as a quality predictor, which can be easily measured over the whole grape-ripening period. The rate of Meso- and microclimatic measurements enzymatic and chemical reactions in grapes, in terms of develop- MCS data loggers, which continually measured temperature and ment and/or degradation of components, is dependent mainly on visible light radiation (300-1200nm) over the whole ripening temperature and light radiation. Therefore these two climatic period on an hourly basis, were installed within selected vine parameters were used as variables. Canopy density, which is a canopies in the vicinity of the clusters, as well as above the function of different climatic and viticultural factors, largely canopies. Each radiation sensor consisted of 10 individual sen- determines the effects of temperature and light radiation. sors, fitted in parallel onto a metre-long rod, thus giving a more

S. Afr. J. Enol. Vitic., Vol. 22, No. 1,2001

22 A Model for Predicting Sauvignon blanc Wine Quality 23 reliable average reading within the canopy (Marais et a/., 1996; ter plots were examined for trends. After examining the scatter 1999). These measurements were done in each experimental unit. plots, it was clear that the radiation variable showed a non-linear Aroma component analyses trend. Therefore three additional terms were added (i.e. the squares of the above- and within-canopy light radiation and the Grape samples from each treatment, region, season and replicate interaction between them) before the data were subjected to the were analysed for free and bound monoterpenes and bound Ci3- stepwise regression procedures. For each dependent variable a norisoprenoids by gas chromatography, and for 2-methoxy-3- stepwise regression was performed with a specified significance isobutylpyrazine (ibMP) by gas chromatography / mass spec- level of at least 5% for inclusion in the models, using SAS trometry (Marais et al., 1996; 1999). (Version 6.12 ) statistical software (SAS, 1990). Sensory analysis For the above-mentioned analyses, the data were handled in two Wines of each treatment, region, season and replicate were sensori- ways. Firstly, all the data were statistically processed. Secondly, ally evaluated for fruitiness and vegetative/asparagus/green pepper the data obtained at ripeness (fourth ripening stage) only were intensities by a panel of six experienced judges. A line method was statistically processed, since wines were produced from grapes at used, i.e. evaluating the intensity of each characteristic by making a this stage. mark on an unstructured, straight 100 mm line (Marais et al., 1999). RESULTS AND DISCUSSION Statistical procedures The final models produced by the stepwise regression procedures Seventy-two independent data sets consisted of three seasons, are given in Table 1 and Figures 1 to 3 for the complete data set, three localities, two canopy treatments and four ripening stages. and in Table 2 and Figures 4 to 6 for the data of harvest week four Only 70 data sets were used, due to two missing plots. A 15-vine only. These coefficients correspond to significant correlations plot was considered as an experimental unit. For each experi- between dependent and independent variables (data not shown). mental unit the microclimatic measurements, such as the mean The figures presented were selected with the main purpose of this maximum, mean minimum and average temperatures during a study in mind, i.e. to predict wine quality from easily-measurable ripening week, were calculated and served as independent vari- microclimatic parameters. Although ibMP was significantly ables. The average light radiations above and within the canopies described by the interaction of above- and within-canopy radia- were also recorded as independent variables. The grape and wine tion, only 43.4% of the variation could be explained by the model measurements (averages of three replicates), such as aroma (Table 1, Fig. 1). For fruitiness intensity 33.3% of the variation volatiles (monoterpenes, norisoprenoids and ibMP) and sensory was explained by maximum temperature and the above-canopy data (fruitiness intensity and vegetative/asparagus/green pepper radiation (Table 1, Fig. 2). The vegetative/asparagus/green pepper intensity) were recorded as dependent variables. intensity (complete data set) showed the best coefficient of deter- Pearson's correlation coefficients were calculated between the mination, i.e. R2 = 68.8% (Table 1, Fig. 3). The above-canopy above-mentioned independent and dependent variables and scat- radiation showed a greater effect than the within-canopy radia-

TABLE1 Coefficients of independent variables selected for model and standard errors. Models fitted to all the data (N=70).

Variable Intercept T min. T max. T aver. A W AxW A2 W2 R2

65.4387 -2.3810 37.2% Mono! ±8.0075 ±0.3752 sl<0.01 37.8475 -0.5634 6.8% Noris ±5.9782 ±0.2537 sl=0.03

91.8313 -2.8195 -14.8243 0.5092 43.4% ibMP ±17.5359 ±0.7455 ±3.9360 ±0.1616 sl<0.01

21.9055 -1.0191 2.1351 33.3% ±10.4858 ±0.4318 ±0.3767 sl<0.01

265.119 -15.6791 -8.3895 0.3043 0.5505 68.8% Vagp ±29.648 ±2.6458 2.9499 ±0.0590 ±0.2492 sl<0.01

Monot = Total free monoterpenes {relative concentration) Noris = Tota! bound monoterpenes and Cn-norisoprenoids (relative concentration) ibMP = 2-Methoxy-3-isobutylpyrazine concentration (ng/L) Fi = Fruitiness intensity (%) Vagp = Vegetative/asparagus/green pepper intensity (%) A = Visible light radiation above the canopy (MJ) W = Visible light radiation within the canopy (MJ) T min. = Minimum temperature (°C) T max. Maximum temperature (°C) T aver. = Average temperature (°C) _ = Not selected

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2001 24 A Model for Predicting Sauvignon blanc Wine Quality

TABLE 2 Coefficients of independent variables selected for model and standard errors. Models fitted to the data from harvest week four only (N= 18).

Variable Intercept T min, T max, T aver. A W AxW A2 Wz R2

66.5851 -1.7250 — — — Monot — — — 70.5% ±8.3672 ±0.2792 sl<0.01 Noris — — — — — — _ _ _ _ ibMP 146.6720 — — — -11.9510 — — 0.2516 — 40.8% ±55.4550 ±3.1776 ±0.1180 sl=0.02

Fi 6.7709 — — — 1.5152 — — — — 22.7% ±16.2588 ±0.6995 sl=0.046 _ 0.4499 — 65.0% Vagp 313.451 — — — -22.3616 — ±82.2622 ±7.6806 ±0.1750 skO.Ol

Monot = Total free monoterpenes (relative concentration) Noris = Total bound monoterpenes and Cj3-norisoprenoids (relative concentration) ibMP = 2-Methoxy-3-isobutylpyrazine concentration (ng/L) Fi = Fruitiness intensity (%) Vagp = Vegetative/asparagus/green pepper intensity (%) A = Visible light radiation above the canopy (MJ) W = Visible light radiation within the canopy (MJ) T min. = Minimum temperature (°C) Tmax. = Maximum temperature (°C) T aver. = Average temperature {°Q — = Not selected

Y = 91.83 - 2.819A - 14.824W + 0.5Q92AxW R = 43.4% si < 0.01 Y = 21.9055 • 1.019T max. + 8.1351A R2= 33.3% si < 0.01 f*• t^

rM '«Won(Mj, " ^ -*"

FIGURE 1 FIGURE 2 Effect of above-canopy (A) and within-canopy (W) radiation Effect of above-canopy (A) radiation and average maximum (between veraison and ripeness) on 2-methoxy-3-isobutyl- temperature (T max.) (between veraison and ripeness) on pyrazine concentration in Sauvignon blanc grapes. the fruitiness intensity of Sauvignon blanc wine. tion. The higher the average above-canopy radiation, the lower ation in monoterpene levels was explained by the average maxi- the vegetative/asparagus/green pepper intensity of the wine (Fig. mum temperature for the week in which the grape samples were 3). This is in agreement with data presented by Marais et al. taken. Monoterpenes may contribute to the flower-like nuances of (1999). Although natural shading plays an extremely important Sauvignon blanc wine, but are probably less important than the role in Sauvignon blanc quality development (Marais et al., cultivar-typical methoxypyrazines. The negative coefficient indi- 1999), models developed separately for the shaded and control cated that the higher the maximum temperature, the lower the treatment data were more or less the same as for the full data set monoterpene concentrations in the grapes, which is in agreement and are therefore not reported. with results reported by Marais et al. (1999), There was not Models arising from the data of ripening week four (harvest enough evidence, i.e. no variables were selected, to fit a model on time) only are presented in Table 2. As much as 70.5% of the vari- the norisoprenoids in the grapes. 2-Methoxy-3-isobutylpyrazine,

S. Afr. J. Enol. Vitic., Vol. 22, No. 1, 2061 A Model for Predicting Sauvignon blanc Wine Quality 25

35 Y = 146.672 - 11.9510A + 0.2516A

Y = 265,119 - 15.6791A 4- 0.3043A g 30 - 8.3B95W + 0.5505W R = 40.8% si = 0.02 25 = 68.6% si < 0.01 Is IQ.DT) 20 ««s« A£ 15

10

5 —

12 14 16 18 20 22 24 26 26 30 Above-canopy radiation (MJ)

FIGURES FIGURE 4 Effect of above-canopy (A) and within-canopy (W) radiation Effect of above-canopy (A) radiation at harvest (week 4) on (between veraison and ripeness) on the vegetative/asparagus/ 2-methoxy-3-isobutylpyrazine concentration in Sauvignon green pepper intensity of Sauvignon blanc wine. blanc grapes.

70 100 Y = 313.451 - 22.3616A + 0.4499A 60 R = 65.0% si < 0.01 80 50

* 40 60

30 S." iS5 40

.*• 20 Y = 6.7709 + 1.5152A 10 R = 22.7% si = 0.046

12 14 16 18 20 22 24 26 28 30 12 14 16 18 20 22 24 26 28 30 Above-canopy radiation (MJ) Above-canopy radiation (MJ) FIGURES FIGURE 6 Effect of above-canopy (A) radiation at harvest (week 4) Effect of above-canopy (A) radiation at harvest (week 4) on on fruitiness intensity of Sauvignon blanc wine. vegetative/asparagus/green pepper intensity of Sauvignon blanc wine.

fruitiness intensity and vegetative/asparagus/green pepper inten- CONCLUSIONS sity showed a significant response to the above-canopy radiation There is a significant relationship between gas chromatographi- only (Figs. 4, 5 and 6, respectively). Again the vegetative/aspara- cally-analysed grape aroma components, sensorially-evaluated gus/green pepper intensity variation was best explained by a qua- wine quality parameters and microclimatic data. Models are pre- dratic response of above-canopy radiation with 65.0%, and a min- sented, one of which can predict Sauvignon blanc wine quality imum turning point of 24.9% for the above-canopy radiation. In (cultivar-typical vegetative/asparagus/green pepper intensity ^ spite of the fact that only 18 data points were applied for ripening from above- and within-canopy radiation data, collected ovei week four, results obtained for vegetative/asparagus/green pepper grape ripening, with a fairly high degree of accuracy. It is there- intensity (65.0%, Table 2) were close to those of the full data set fore possible to predict wine quality from easily-measurabh (68.8%, Table 1). microclimatic data. The results of this investigation wert

S. Afr. J. Enol. Vitic., Vol. 22, No. 1,2001 26 A Model for Predicting Sauvignon blanc Wine Quality obtained under specific South African conditions and it is not Holgate, A., 2000. Berry colour index assay - application and interprelation of the claimed that they are valid under all conditions. Nevertheless, assay as an objective measure of red wine grape quality in a commercial vineyard. Proc. 5th Int. Symp. Cool Climate Vitic. & Enol., 16-20 January 2000, they can be considered as a contribution towards wine quality Melbourne, Australia. In press. prediction. Future research is necessary to test and refine this model for application under different environmental conditions. Le Roux, E.G., 1974. 'n Klimaatsindeling van die Suidwes-Kaaplandse wyn- bougebiede. M.Sc. Thesis, University of Stellenbosch, StelSenbosch, South Africa.

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