terroir influence on water status and nitrogen status of ... · terroir effect on vine vigour, must...

Terroir Influence on Water Status and Nitrogen Status of non-IrrigatedCabernet Sauvignon (Vitis vinifera). Vegetative Development, Must andWine Composition (Example of a Medoc Top Estate Vineyard, Saint JulienArea, 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, France2) ENITA de Bordeaux, 1 Crs du General de Gaulle, 33175 Gradignan Cedex, France

Submitted for publication: March 2000Accepted for publication: January 2001Key words: Terroir, Nitrogen, water status, Vitis vinifera, Cabernet Sauvignon, vigour, anthocyanin, phenolic content, must nitrogen

content, leaf water potential

Terroir effect on vine vigour, must composition and wine quality was investigated for Cabernet Sauvignon duringa rainy vintage in a top estate of the Medoc area (Bordeaux, France). Soil was the only variable in this survey. Vinewater status was determined by means of leaf water potential. Mild water deficits were observed only on a gravellysoil with a shallow root zone. Vine nitrogen status was determined by total must nitrogen content. Nitrogen statusvaried from deficient to unlimited. Nitrogen deficiency reduced vine vigour to a greater extent than did mild waterdeficits. The smallest berries, as well as the highest phenolic content for both must and wine, were observed undernitrogen deficiency. Both early mild water deficits and a nitrogen deficiency throughout the growth period weredemonstrated to have beneficial effects on the phenolic content of berries and on wine quality. Two combinationsof vine water status and vine nitrogen status led to the most highly appreciated wines: a low nitrogen status withoutwater deficits and a medium nitrogen status accompanied by mild water deficits.

For any given vineyard terroir can be described as the combina-tion of pedoclimatic conditions, vine components such as culti-var, clone and rootstock as well as viticultural techniques (prun-ing system, canopy management, etc.). Given this, terroir must beseen as a complex system with multiple variables: it is impossi-ble to study all the variables in one experiment. Within a singleestate (10 to 100 ha) in Bordeaux, there is generally no climaticvariation but several types of soil. It is well known that the effectof the soil on vine behaviour is mediated through varying water-content levels and their effects on vine water status (Seguin,1970; Seguin, 1986; Van Leeuwen & Seguin, 1994). Waterdeficits occur when transpiration exceeds the ability of the rootsystem to supply water to the transpiring leaves. Mild waterdeficits are known to have positive effects on reducing berry size(Smart, 1974) and on berry skin anthocyanin and tannin contentin red grape varieties (Matthews & Anderson, 1988; VanLeeuwen & Seguin, 1994; Koundouras et al, 1999). Schultz andMatthews (1993) observed that in potted vines water deficitscaused embolism in the xylem shoot apex, which stopped shootgrowth. This has been confirmed in field studies (Matthews et al,1987; Van Leeuwen & Seguin, 1994; Naor & Wample, 1996).Given this consideration, it can be said that under mild waterdeficits vegetative growth is no longer in competition with repro-ductive development as a sink of photosynthesis resources. Hencefruits are primary sinks. This can partly explain the richer mustand wine constitution obtained from vines having undergone mildwater deficits.

Without the addition of nitrogen fertiliser, vine nitrogen statusdepends upon soil organic matter content, its mineralisation rateand the C/N ratio. It has been shown for Merlot (Delas et al,1991) and for Thompson seedless and White Riesling (Kliewer

and Cook, 1971; Spayd et al, 1994) that nitrogen fertilisationincreases vigour.

In the Bordeaux oceanic climate rainfall can vary to a consid-erable extent from one season to another. In a dry season, such as1990, high enological berry potential and therefore wine qualityare strongly linked to mild water deficits (Van Leeuwen andSeguin, 1994). In a rainy season, this is less likely to occur eventhough a soil effect on wine quality is generally admitted to existdespite the rainy conditions. As a better understanding of the ter-roir effect can help growers in their vineyard management andgrape selection, the effect of soil variation on vine vigour, berryconstitution and wine quality was investigated in this survey dur-ing a rainy vintage. Vine water status and vine nitrogen statuswere measured by means of physiological indicators. In the casestudied soil was the only variable differentiating blocks plantedwith the same cultivar and rootstock and with the same vine spac-ing and subject to the same canopy management. Conradie(1986) demonstrated that vine nitrogen uptake from bud breakthrough fruit maturity is progressively less utilised for vegetativegrowth and increasingly more utilised by the fruit. This was con-firmed by Soyer et al (1995), who showed that vine berry nitro-gen content closely reflected mineral nitrogen availability in thesoil. Thus, berry total nitrogen content can be used as a physio-logical indicator of vine nitrogen status. However, the levels oftotal nitrogen berry content as an indicator of vine nitrogen statusis poorly documented.MATERIALS AND METHODSExperimental location and plant materialThe study was conducted in Leoville Las Cases vineyard. Saint-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 pedologicaltypes spread over only 100 ha. Four blocks planted with Vitisvinifera cv. Cabernet Sauvignon grafted on Vitis riparia L. root-stock were studied. Vine age was between 24 and 31 years. Thefour blocks were identified as 1G, 3 A, 4H and 5P. Each block wasset up on a different soil type. To avoid soil variation inside ablock, only 100 vines were studied per site, all located around thesoil pit studied. The soil type, texture, percentage of organic mat-ter in fine soil, occurrence of water table and root zone depth arepresented in Table 1.

The four blocks were less than 500 m apart. The altitude of thefour blocks varied from 10 to 20 m and row orientation was iden-tical. Hence it was accepted that no climatic variation occurredamong the four blocks. This was confirmed by the vine phenolo-gy in 1997, which was similar for all the terroirs studied (bloom:May 25; veraison: July 21). The vines were spaced 1 x 1.1 mapart and double Guyot pruned; trunk height was 0,4 m from thesoil surface. During vegetative development, vine canopy wasmechanically cut at 1.1 m height for every block.Water potentialsPre-dawn leaf water potential (dawn^) and leaf water potential(leaTf) were measured with a pressure chamber (Scholander etal, 1965) equipped with a digital manometer (SAM Precis 2000,33175 Gradignan, France). DawnY was measured at the end ofthe night on uncovered mature leaves. LeaPf was measured onmature leaves exposed to sunlight, whether they were transpiringor not (Turner, 1981).Nitrogen statusAs in the preceding years, no nitrogen fertiliser was added in1997. Hence vine nitrogen uptake resulted mainly from mineral-isation of organic matter. Vine nitrogen uptake was estimatedweekly, from veraison through harvest, by the berry total nitrogencontent (Bell et al, 1979).Vine vigourDry leaf mass was measured on eight vines per terroir just beforeharvest. Leaf area per vine was deduced from the correlationobtained. Average total bunch mass per vine was measured on 30vines per block on the day of harvest. Average pruning mass pervine was determined on 25 vines per block.Must characteristics from veraison through harvestFrom veraison through harvest one thousand berries were sam-pled weekly at random from 100 vines on each site. These berries

were immediately counted and weighed to determine averagefresh berry mass. Berries were pressed and the juice was gentlycentrifuged to remove suspended solids. Sugar content was mea-sured by refractometry. Titratable acidity was measured manual-ly with Bromothymol blue. The titration was done with 0.1 NNaOH to an end point of pH 7.0. Malic acid was determinedusing an enzymatic kit from Boehringer Mannheim.

On 200 berries anthocyanins were determined by the method ofRibereau-Gayon & Stonestreet (1965). The measurement ofabsorbency was conducted at a wavelength of 520 nm (opticaldistance: 1 cm). Tannins were measured by the 1PT: "indice despolyphenols totaux" (Ribereau-Gayon, 1970). The wavelengthused was 280 nm (optical distance: 1 cm).Micro vinifi cationMicrovinification was conducted identically for all lots. For everyterroir 50 kg of fruit were harvested on the same day (September27). The fruit from each block was crushed and stems wereremoved. For every lot 40 kg were put into a SOL stainless steeltank. In order to have similar wine alcohol content for tasting, 1G,3A and 5P must were chaptalised to obtain the same sugar con-tent as found in 4H. Alcoholic fermentation and malolactic fer-mentation were enhanced with a selected yeast strain and a select-ed bacteria strain, respectively. All the wine-making parameters(fermentation arrd maceration temperature, pumping over fre-quency, draining away, etc.) were similar.Wine tastingWines were tasted blindly by a panel of 15 professional tasters.They were noted by positive preference order from 1 to 4. Thescores of all judges for a wine were summed. Least significantdifference (LSD) was determined by a modified Chi2.StatisticsWater potential and vigour indicators data were analysed with theANOVA procedure and the Newman Keuls test to determine leastsignificant difference (Statbox Pro Software).RESULTSWater statusSoil water content was at a field capacity on all the soils studiedin the spring (April), which is usual in the French oceanic area. Inthe Medoc 1997 was a rainy vintage: the rainfall in May, June andAugust was far above the average calculated over a 39-year span.Conversely, rainfall was a bit less than average in July andSeptember (Table 2). From bloom through veraison total rainfall

TABLE 1Soil and rooting characteristics of the studied plots.

1G 3A 4H 5P

Type of soil

Gravel contentWater tableTexture of fine soil in limitsof root zone depthOrganic matter (% in finesoil) in the top 60 cmRoot zone depth (meter)

Neoluvisol ongravely soil

75%no

Sandy clay

1.51

Planosol sedimorphe withheavy clay subsoil

15%no

Heavy clay

1.21.5

Redoxisol with heavyclay subsoil

50%yes

Sandy clay

0.50.7

Podzosols

15%no

Sandy

22


20 lerroir influence on Water and Nitrogen Status oj l^atternel bauvignon

TABLE 2Monthly rainfall in Saint Julien in 1997, compared with the long-term average.

May June July August September

Rainfall1997 (mm)Average rainfall1961-1990 (mm)

158.4

77.3

146.6

56.2

36

46.5

80

54.2

32.2

74.1

was 18 mm and from veraison to harvest 113 mm. From Julythrough September 1997 5P dawnT data varied from -0.10 to -0.17 MPa, whereas over the same period IG dawn¥ data variedfrom -0.12 to -0.30 MPa (Fig. 1). At three different stages (July,August and September), dawn*F data were significantly lower forIG than for the other blocks.

On August 23 midday leaf water potential showed no differ-ences among the 4 soils (Fig. 2). Yet IG leaf water potential wassignificantly more negative than that of the other locations at theend of the afternoon, being the beginning of the recovery periodof vine water status. This confirmed the lower pre-dawn leafwater potential measured on IG during the same period. Climaticconditions were identical for the four blocks studied. Thus waterstatus differences observed in 1997 reflected mostly soil ability tosupply water to the vine. Hardie & Considine (1976) and VanLeeuwen et al (1994), showed that dawnY of -0.30 MPa reflect-ed a mild water deficit, which induced slackening of shootgrowth. Given this, IG can be considered as the only block wherevines underwent mild water deficits in 1997.

As IG received as much rainfall as 5P, where no water deficitoccurred, IG water deficits reflected low water-storage capacity,due to a high proportion of gravel in the shallow root zone (Table1). Conversely, on 5P the root zone was twofold deeper than onIG, whereas the gravel content in the root zone was fivefoldlower. These conditions were reflected in the high dawnT datacollected from July to September on 5P. On 4H, despite the shal-

low root zone, no water deficits were detected. This was due to apermanent water table linked to the subsoil clay depression.Conversely, on 3A the subsoil clay is convex. Thus no water tablecan be formed ant the root zone is deeper (Table 1).Nitrogen statusFrom veraison through harvest, berry total nitrogen content for4H was threefold lower than for 5P and twofold lower than for IG(Fig. 3). Berry total nitrogen content of 3A was between that of4H and of IG. Throughout this period the difference betweenberry total nitrogen content appeared to remain constant from oneblock to another.

Lower total nitrogen content for 4H reflected the low organicmatter content in this soil (Table 1). Conversely, 5P soil organicmatter percentage was fourfold higher than for 4H, with totalberry nitrogen being threefold higher than for 4H. Thus, under theconditions of this survey, berry total nitrogen content appeared toreflect soil organic matter content closely.Vine vigourA strong correlation between leaf area (measured with a planime-ter) and dry leaf mass was established. Total leaf area per vine(Table 3) was not significantly different for IG, 3A and 4H, indi-cating that total leaf area per vine was not affected by water sta-tus for these 3 blocks. Hence, IG mild water deficits were onlydue to low soil-water content available in the root zone depth.Moreover, significantly larger total leaf area per vine did notenhance water deficits on 5P. This confirmed the higher soil-water content in the root zone depth of 5P.

The significantly lower total leaf area per vine for 4H, in com-parison to 5P was not due to water status, which was similar forboth terroirs. The lower vine nitrogen status on 4H appeared toexplain its weaker vigour. Furthermore, the total pruning massper vine and the total cluster mass per vine were also significant-ly lower on 4H than on 5P.

As with total leaf area per vine, 4H and IG showed no signifi-cant difference for total pruning mass per vine, nor for total leafarea per vine. Two vigour indicators, total bunch mass per vine

-0,2--

(0 -0,25Q)

-0,35JULY AUGUST SEPTEMBER

FIGURE 1Dawn 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

-1,602:24

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

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 2Diurnal 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 - -

1 5 0 - -

120 -

90- -SEPTEMBER

FIGURESBerry total nitrogen content from veraison through harvest (1997).

TABLE 3Vigour indicators: Total leaf area, total pruning mass and totalbunch mass per vine.

1G 3A 4H 5P

Total leaf area pervine (m2)Total pruning massper vine (kg)Total bunch massper vine (kg)

1.01 a'1)

0.24 a b

0.935 a b

0.96 a

0.31 b

1.09b

0.8 a

0,19 a

0.765 a

1.46 a

0.43 c

1.103b

(') Values within rows followed by the same letter do not differ significantly.

and total shoot mass per vine, showed that 3A was significantlymore vigorous than 4H, but no more than 1G. Thus the differencein nitrogen supply between 3A and 4H, which had the same water

status, seemed to have had more influence on vigour than did variations in water status between 1G and 4H or between 1G and 3A

Total leaf area per vine and total pruning mass per vine for 51were significantly higher than for the 3 other terroirs, while 51total cluster mass was significantly higher than 4H only. As thttrellising and pruning system were the same on the four sites, thiishowed that low nitrogen status on 4H reduced total bunch mas:per vine to a greater extent than did the mild water deficits on 1GThis further emphasised that low vine nitrogen status had ;greater influence on vigour than did mild water deficits befortveraison.Fresh berry massFrom veraison through harvest 5P fresh berry mass was constantly 30% higher than that of 4H, whereas it was only 10% to 15 9ihigher than that of 1G and 3A (Fig. 4). Fresh berry mass and totacluster mass per vine showed a strong linear correlation (R2=0.92


12 Terroir Influence on Water and Nitrogen Slalus of Cabeme! Sauvignon

160

150

140

70 - •

60

230 y-

220 - •

210--

200 - •

190 --

180 -•

170 --

160 -

150 -•

140-•

130 -•

120-•

1 1 0 - -

100 - -

90-

3A

-1G

-4H

-5P

AUGUST SEPTEMBER

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

AUGUST SEPTEMBER

FIGURESMust-reducing sugar content evolution from veraison through harvest (1997).

440,0

•3-Q>

JULY AUGUST SEPTEMBER

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


Terroir Influence on Water and Nitrogen Status of Cabernet Sauvignon 13

SEPTEMBER

FIGURE?

Must malic acid (meq/L) content evolution from two weeks post-veraisonthrough harvest (1997).

1400

1300-

— 1200 -

1 "'

C

700 - -

600-•

500

400

3A

1 G

AUGUST SEPTEMBER

FIGURESMust anthocyanin content evolution from two weeks after veraison through

harvest (1997).

n=4), which demonstrated that flower abortion did not explain theyield difference between the sites.

Low fresh berry mass on 4H confirmed the low vigour previ-ously observed. Lower fresh berry mass on 1G and 3 A, comparedto 5P, can be attributed to mild water deficits and lower nitrogenstatus respectively, even though these are not reflected by signif-icant differences in total cluster mass per vine.

Berry composition through ripening

Must from 4H and 1G exhibited the highest sugar content and thelowest acidity, whereas the reverse was true on 5P (Figs. 5, 6 and7). Must sugar content was less for 1G than for 4H. Even thoughtitratable acidity on 1G and 4H was similar, malic acid contentwas nevertheless lower on 1G. As already shown by Van Leeuwenand Seguin (1994), vine water deficits enhance low must malic

acid content. For the four sites a strong linear correlation(R2=0.97; n=4) between average dawn*JK data (from July throughSeptember) and berry malic acid content at the harvest wasobserved.Anthocyanins, tannins and wine appreciationAnthocyanin content for 4H was almost twofold higher than for 3Aand 5P, whereas the difference between 4H and 1G was less pro-nounced (Fig. 8). IPT differences followed the same hierarchy,with 4H and 1G exhibiting the highest tannin content (Table 4).The professional panel of tasters distinguished 4H and 1G as thebest wines (Table 4). The most appreciated wines were also thehighest in phenolic content. Wine phenolic content correlatedclosely with phenolic content (Table 4). Must phenolic content for3A, 4H and 5P suggested that low nitrogen status without waterdeficits was linked to high enological potential for a red grape vari-


TABLE 4Must phenolic content at the harvest, wine phenolic content andwine-tasting appreciation.

1G 3A 4H 5P

Must anthocyanin contentat harvest (mg/L)Must tannin content atharvest (IPT)(1)

Wine anthoeyanincontent (mg/L)Wine tannin content (IPT)

Wine-tasting sum rate

33

61154

823

29.8

46350

50.5a(2) 39 b

1180

36.5

73070

58 a

748

40143

21 c

(i) IPT = "indice des polyphenols totaux".<2> Values within rows followed by the same letter do not differ significantly.

ety such as Cabernet Sauvignon. This confirmed the result ofKeller and Hrazdina (1998) on continuously irrigated, pottedCabernet Sauvignon. They observed that excessive nitrogen fertili-sation decreased win phenolic content. In a rootstock trial Delas etal. (1991) observed an increase of phenolic grape content for someof the rootstocks where nitrogen fertilisation was not applied.Hence, both early mild water deficits and lower nitrogen statusthroughout the growth period had beneficial effects on total berryphenolic contents and wine quality. This appeared to be linked tothe limiting effect on the vine vigour of both of these factors.DISCUSSIONWith the same water status for both sites, lower nitrogen status on4H than on 5P induced a decrease in vigour. The total leaf areaper vine, the total pruning shoot mass per vine and the total clus-ter mass per vine were respectively 55%, 44% and 30% lower on4H than on 5P. Considering these vigour indicators, 4H under-went a clear nitrogen deficiency in 1997. The total cluster massper vine represented a calculated yield of 6.5 tons per ha for 4H,suggesting that nitrogen deficiency level was moderate, as itallowed an acceptable yield for a high-quality wine-producingvineyard.

Bell et al (1979) reported on continuously irrigated Thompsonseedless that for a total nitrogen content of must at harvest rang-ing from 287 to 754 mg/L no significant difference occurred incrop mass per vine. Kliewer and Cook (1971) showed on pottedvines that leaf area and trunk circumference increased linearlywith increasing concentrations of nutrient solutions ranging from0 to 4 mM of NOs, whereas they remained constant with concen-trations ranging from 4 to 8 mM of NOs. This suggests that theBell et al (1979) range of must total nitrogen content indicated nolack of nitrogen, because it was superior to the threshold valuewhere nitrogen begins to have an effect on vigour. In 1997 5Pmust total nitrogen content (290 to 370 mg/L from veraisonthrough harvest) fell within this range. Given this, 5P must totalnitrogen data reflected no limiting vine nitrogen status. Moreover,3A must total nitrogen content (185 to 230 mg/L) correspondedto an intermediate level of vine nitrogen status, between those of5P and of 4H. This was emphasised by the fact that 3A vigour,estimated by the total pruning mass per vine and the total clustermass per vine, was significantly lower than that of 5P and signif-icantly higher than that of 4H, with no water status difference.

Conradie (1980, 1986) demonstrated that most of the vine nitro-gen uptake occurs from bud burst through veraison. During thisperiod nitrogen is increasingly allocated to fruit. From veraisonthrough harvest Conradie (1991) observed a translocation onChenin blanc of nitrogen from shoot, leaves and permanent struc-ture to bunches. These observations were confirmed by constant orslightly increasing must total nitrogen content on the 4 sites in 1997,from veraison through harvest, despite different rates of berry diam-eter increase (Figs. 3 and 4). Low nitrogen status for 4h can thus beconsidered as reflecting limited vine nitrogen uptake since budbreak. This could explain why the low nitrogen status of 4H reducedvigour more than did 1G mild water deficits for 1G. 4H low nitro-gen status was constant through the vegetative and the reproductiveperiods (Fig. 3), whereas 1G mild water deficits appeared at the endof fruit set and were not permanent until harvest (Fig. 1).

Further investigations will be necessary to define more accu-rately the range of total nitrogen content in must leading to thebest must and wine quality. Different total nitrogen contents dataon 1G and 4H indicated that a nitrogen status varying from lowto medium favoured the production of highly appreciated wine inthis Bordeaux top estate. Yet 1G and 3A grape total nitrogen con-tent data suggested that a medium nitrogen status was adequate toobtain a high-quality wine, if associated with mild vine waterdeficits. Conversely, under the conditions of this survey, withoutvine water deficits only nitrogen deficiency on 4H (90 to 150mg/L of total must nitrogen) had an obvious positive effect onmust and wine phenolic content. This positive effect on winequality suggested that nitrogen deficiency should be maintainedin the vineyard and that nitrogen deficiency in must should becorrected in the tank before and/or during the fermentationprocess. This practice is already followed with success in severalBordeaux vineyard areas.CONCLUSIONSThis terroir survey, carried out during a rainy season in theBordeaux area, revealed a soil effect on vine nitrogen status mea-sured by must total nitrogen content. Despite the rainy vintage, weobserved on a gravelly soil (1G) mild water deficits linked to lowsoil water content in the shallow root zone. Low nitrogen statuswas found on soil having a particularly low organic matter content(4H). We observed that low nitrogen status reduced vine vigourmore than did mild water deficits. Yet when vines were subject toone of these limiting factors, the wines produced in this Bordeauxtop estate were of significantly higher quality. Low vine nitrogenstatus induced high berry tannin and anthocyanin content, accom-panied by low berry mass. It also reduced yield, but this may beacceptable in a very high-quality grape-producing vineyard.

Considering the benefits of low vine nitrogen status on the phe-nolic content of must and wine, it remains to define how this lownitrogen status can be managed more accurately in order to con-serve the equilibrium between the highest possible wine qualityand a decreased but economically acceptable yield.

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Conradie, W.J., 1980. Seasonal uptake of nutrients by Chenin blanc in sand cul-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 timeof application and soil type. S. Afr. J. Enol. Vitic. 2, 76-82.

Conradie, W.J., 1991. Distribution and translocation of nitrogen absorbed duringearly summer by two-year-old grapevines grown in sand culture. Am. J. Enol.Vitic. 42, 180-190.Delas, J. Molot, C. & Soyer, J.P., 1991. Effects of nitrogen fertilisation and graft-ing on the yield and quality of the crop of Vitis vinifera cv. Merlot. Proceedingsof the International symposium on nitrogen in grapes and wine, Seattle, pubbshedby The American Society for Enology and Viticulture. 242-248.

Hardie, W.J. & Considitie, J.A., 1976. Response of grapes to water deficit stressin particular stages of development. Am, J. Enol, Vitic. 2, 55-61.

Keller, M. & Hrazdina, G., 1998. Interaction of nitrogen availability during bloomand light intensity during veraison. II. Effects on anthocyanin and phenolic devel-opment during grape ripening. Am. J. Enol. Vitic. 49, 341-349.

Kliewer, W.M. & Cook, J.A., 1971. Arginine and total free amino acids as indica-tors of the nitrogen status of grapevines. Am. J. Enol. Vide. 96, 581-587.

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Matthews, M.A. & Anderson, M.M., 1988. Fruit ripening in Vitis vinifera L.:Responses to seasonal water deficits. Am. J. Enol. Vitic, 39, 313-320.

Naor, A. & Wample, R.L., 1996. Diurnal internode growth rate in field-grown'Concord' (Vitis labrusca) grapevines. J. Hortic. Sci. 71, 167-171,

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Schultz, H.R. & Matthews, M.A., 1993. Xylem development and hydraulic con-ductance in sun and shade shoots of grapevine (Vitis vinifera L.), evidence thatlow light uncouples water transport capacity from leaf area. Planta 190, 393—406.

Seguin, G,, 1970. Les sols des vignobles du Haut-Medoc. Influence sur 1'alimen-tation en eau de la vigne et sur la maturation du raisin. These de doctoral d'etat,Faculte des Sciences, Universite de Bordeaux.

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Soyer, J.P., Molot, C., Bertrand, A., Gazeau, O., Lovelle, B.R. & Delas, J., 1996.Influence de I'enherbement sur 1'alimentation azotee de la vigne et sur la compo-sition des moflts et des vins. In: Oenologie 95, Actes 5e Symp. Inter. Oenologie,Bordeaux. Tec Doc ed., Paris. 81-84.

Spayd, S.E., Wample, R., Evans, R.G., Stevens, R.G., Seymour, B.J. &Nagel,C.W., 1994. Nitrogen fertilisation of white Riesling grapes in Washington. Mustand wine composition. Am. J. Enol. Vitic. 45, 31-41.

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Relationship Between Microclimatic Data, Aroma ComponentConcentrations and Wine Quality Parameters in the Predictionof Sauvignon blanc Wine QualityJ. Marais1, F. Calitz2 and P. D. Haasbroek3

1) ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa2) ARC Biometry Unit, Private Bag X5013, 7599 Stellenbosch, South Africa3) ARC Agromet, Private Bag X5013, 7599 Stellenbosch, South Africa

Submitted for publication: September 2000Accepted for publication: April 2001Key words: Microclimate, temperature, radiation, Sauvignon blanc quality, prediction model

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

Over many years research has been aimed at developing a simplemodel or recipe that could define and predict wine quality.Examples are sugar/acid ratio (°B/TTA) (Du Plessis & VanRooyen, 1982), the glycosyl-glucose (G-G) assay (Francis et al,1998) and the red wine colour index (Holgate, 2000). Such amodel should also be useful as a method to compensate the grapeproducer according to grape quality. The aim further is that themodel should incorporate parameters that are easily measurableunder field conditions, instead of parameters such as aromaimpact volatiles, the quantification of which is dependent oncomplicated and expensive gas chromatographic and mass spec-trometric analyses. Due to the complexity of factors affectinggrape and wine composition and quality, attempts to date haveachieved varying degrees of success and a foolproof, simplemodel still has to be developed. Nevertheless-, earlier attemptswere valuable and all contribute something to the eventual solu-tion of this problem.

Significant correlations between microclimatic parameters andwine sensory characteristics were reported earlier (Noble, Elliot-Fisk & Alien, 1995). Models using light radiation in the predic-tion of photosynthesis under field conditions, were also devel-oped (Blackburn & Proctor, 1983; Goudriaan, 1986; Spitters,1986; Haasbroek, Myburgh & Hunter, 1997). Photosynthesis isdependent on light radiation and temperature and is indirectly animportant factor in grape composition development.

The approach in this study was to investigate the possible useof microclimatic parameters as a quality predictor, which can beeasily measured over the whole grape-ripening period. The rate ofenzymatic and chemical reactions in grapes, in terms of develop-ment and/or degradation of components, is dependent mainly ontemperature and light radiation. Therefore these two climaticparameters were used as variables. Canopy density, which is afunction of different climatic and viticultural factors, largelydetermines the effects of temperature and light radiation.

The purpose of this study was to correlate microclimatic data(temperature and radiation) with aroma component concentra-tions and wine quality parameters of Sauvignon blanc and todevelop a model for predicting wine quality.MATERIALS AND METHODSGrapes, regions and seasonsVitis vinifera L. cv. Sauvignon blanc grapes, grown in three cli-matically different regions, namely Robertson (Region IV, 1945 -2222 degree days), Stellenbosch (Region IE, 1668 -1944 degreedays ) and Elgin (Region II, 1389 - 1667 degree days) (Le Roux,1974), were used. A single canopy manipulation treatment, whichaltered microclimate in a natural way to obtain a higher degree ofshading, was applied in each region (Archer & Strauss, 1989;Marais, Hunter & Haasbroek, 1999). Control vines were notmanipulated. Three replications, consisting of 15 vines per repli-ca, were used. The general viticultural practices followed weredescribed by Marais et al. (1999). Grapes were obtained overthree seasons, namely 1997, 1998 and 1999. Results of the 1997and 1998 seasons were published by Marais et al. (1999) and tri-als during the 1999 season were a repetition of the first two sea-sons.

Grape samples (whole bunches, 2kg per sample) were collect-ed weekly at random from each treatment and replicate over threeweeks between approximately 16°B (close to veraison) and 21°B(ripeness). Grapes were harvested at ripeness (fourth ripeningstage) for wine production, following standard Nietvoorbij prac-tices for small-scale white wine production (Marais et al., 1999).Meso- and microclimatic measurementsMCS data loggers, which continually measured temperature andvisible light radiation (300-1200nm) over the whole ripeningperiod on an hourly basis, were installed within selected vinecanopies in the vicinity of the clusters, as well as above thecanopies. Each radiation sensor consisted of 10 individual sen-sors, fitted in parallel onto a metre-long rod, thus giving a more


22

A Model for Predicting Sauvignon blanc Wine Quality 23

reliable average reading within the canopy (Marais et a/., 1996;1999). These measurements were done in each experimental unit.Aroma component analysesGrape samples from each treatment, region, season and replicatewere analysed for free and bound monoterpenes and bound Ci3-norisoprenoids by gas chromatography, and for 2-methoxy-3-isobutylpyrazine (ibMP) by gas chromatography / mass spec-trometry (Marais et al., 1996; 1999).Sensory analysisWines of each treatment, region, season and replicate were sensori-ally evaluated for fruitiness and vegetative/asparagus/green pepperintensities by a panel of six experienced judges. A line method wasused, i.e. evaluating the intensity of each characteristic by making amark on an unstructured, straight 100 mm line (Marais et al., 1999).Statistical proceduresSeventy-two independent data sets consisted of three seasons,three localities, two canopy treatments and four ripening stages.Only 70 data sets were used, due to two missing plots. A 15-vineplot was considered as an experimental unit. For each experi-mental unit the microclimatic measurements, such as the meanmaximum, mean minimum and average temperatures during aripening week, were calculated and served as independent vari-ables. The average light radiations above and within the canopieswere also recorded as independent variables. The grape and winemeasurements (averages of three replicates), such as aromavolatiles (monoterpenes, norisoprenoids and ibMP) and sensorydata (fruitiness intensity and vegetative/asparagus/green pepperintensity) were recorded as dependent variables.

Pearson's correlation coefficients were calculated between theabove-mentioned independent and dependent variables and scat-

ter plots were examined for trends. After examining the scatterplots, it was clear that the radiation variable showed a non-lineartrend. Therefore three additional terms were added (i.e. thesquares of the above- and within-canopy light radiation and theinteraction between them) before the data were subjected to thestepwise regression procedures. For each dependent variable astepwise regression was performed with a specified significancelevel of at least 5% for inclusion in the models, using SAS(Version 6.12 ) statistical software (SAS, 1990).For the above-mentioned analyses, the data were handled in twoways. Firstly, all the data were statistically processed. Secondly,the data obtained at ripeness (fourth ripening stage) only werestatistically processed, since wines were produced from grapes atthis stage.RESULTS AND DISCUSSIONThe final models produced by the stepwise regression proceduresare given in Table 1 and Figures 1 to 3 for the complete data set,and in Table 2 and Figures 4 to 6 for the data of harvest week fouronly. These coefficients correspond to significant correlationsbetween dependent and independent variables (data not shown).The figures presented were selected with the main purpose of thisstudy in mind, i.e. to predict wine quality from easily-measurablemicroclimatic parameters. Although ibMP was significantlydescribed by the interaction of above- and within-canopy radia-tion, only 43.4% of the variation could be explained by the model(Table 1, Fig. 1). For fruitiness intensity 33.3% of the variationwas explained by maximum temperature and the above-canopyradiation (Table 1, Fig. 2). The vegetative/asparagus/green pepperintensity (complete data set) showed the best coefficient of deter-mination, i.e. R2 = 68.8% (Table 1, Fig. 3). The above-canopyradiation showed a greater effect than the within-canopy radia-

TABLE1Coefficients of independent variables selected for model and standard errors. Models fitted to all the data (N=70).

Variable

Mono!

Noris

ibMP

Vagp

MonotNorisibMPFiVagpAWT min.T max.T aver._

Intercept T min.

65.4387±8.0075

37.8475±5.9782

91.8313±17.5359

21.9055±10.4858

265.119±29.648

T max. T aver.

-2.3810±0.3752

-1.0191±0.4318

A W AxW A2 W2

-0.5634±0.2537

-2.8195 -14.8243 0.5092±0.7455 ±3.9360 ±0.1616

2.1351±0.3767

-15.6791 -8.3895 0.3043 0.5505±2.6458 2.9499 ±0.0590 ±0.2492

R2

37.2%sl<0.01

6.8%sl=0.03

43.4%sl<0.01

33.3%sl<0.01

68.8%sl<0.01

= Total free monoterpenes {relative concentration)= Tota! bound monoterpenes and Cn-norisoprenoids (relative concentration)= 2-Methoxy-3-isobutylpyrazine concentration (ng/L)= Fruitiness intensity (%)= Vegetative/asparagus/green pepper intensity (%)= Visible light radiation above the canopy (MJ)= Visible light radiation within the canopy (MJ)= Minimum temperature (°C)

Maximum temperature (°C)= Average temperature (°C)= Not selected


24 A Model for Predicting Sauvignon blanc Wine Quality

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

Variable

Monot

Noris

ibMP

Fi

Vagp

MonotNorisibMPFiVagpAWT min.Tmax.T aver.—

Intercept T min, T max, T aver. A W

66.5851 -1.7250 — — —±8.3672 ±0.2792

— — — — — —

146.6720 — — — -11.9510 —±55.4550 ±3.1776

6.7709 — — — 1.5152 —±16.2588 ±0.6995

313.451 — — — -22.3616 —±82.2622 ±7.6806

= Total free monoterpenes (relative concentration)= Total bound monoterpenes and Cj3-norisoprenoids (relative concentration)= 2-Methoxy-3-isobutylpyrazine concentration (ng/L)= Fruitiness intensity (%)= Vegetative/asparagus/green pepper intensity (%)= Visible light radiation above the canopy (MJ)= Visible light radiation within the canopy (MJ)= Minimum temperature (°C)= Maximum temperature (°C)= Average temperature {°Q= Not selected

AxW A2 Wz R2

— — — 70.5%sl<0.01

_ _ _ _

— 0.2516 — 40.8%±0.1180 sl=0.02

— — — 22.7%sl=0.046

_ 0.4499 — 65.0%±0.1750 skO.Ol

Y = 91.83 - 2.819A - 14.824W + 0.5Q92AxWR = 43.4% si < 0.01

*• ̂ft

rM'«Won(Mj, " ^-*"

FIGURE 1Effect of above-canopy (A) and within-canopy (W) radiation

(between veraison and ripeness) on 2-methoxy-3-isobutyl-pyrazine concentration in Sauvignon blanc grapes.

Y = 21.9055 • 1.019T max. + 8.1351A

R 2 = 33.3% si < 0.01

FIGURE 2Effect of above-canopy (A) radiation and average maximum

temperature (T max.) (between veraison and ripeness) onthe fruitiness intensity of Sauvignon blanc wine.

tion. The higher the average above-canopy radiation, the lowerthe vegetative/asparagus/green pepper intensity of the wine (Fig.3). This is in agreement with data presented by Marais et al.(1999). Although natural shading plays an extremely importantrole in Sauvignon blanc quality development (Marais et al.,1999), models developed separately for the shaded and controltreatment data were more or less the same as for the full data setand are therefore not reported.

Models arising from the data of ripening week four (harvesttime) only are presented in Table 2. As much as 70.5% of the vari-

ation in monoterpene levels was explained by the average maxi-mum temperature for the week in which the grape samples weretaken. Monoterpenes may contribute to the flower-like nuances ofSauvignon blanc wine, but are probably less important than thecultivar-typical methoxypyrazines. The negative coefficient indi-cated that the higher the maximum temperature, the lower themonoterpene concentrations in the grapes, which is in agreementwith results reported by Marais et al. (1999), There was notenough evidence, i.e. no variables were selected, to fit a model onthe norisoprenoids in the grapes. 2-Methoxy-3-isobutylpyrazine,


A Model for Predicting Sauvignon blanc Wine Quality 25

Y = 265,119 - 15.6791A 4- 0.3043A- 8.3B95W + 0.5505W

= 68.6% si < 0.01

FIGURESEffect of above-canopy (A) and within-canopy (W) radiation(between veraison and ripeness) on the vegetative/asparagus/

green pepper intensity of Sauvignon blanc wine.

35

g 30

Is 25Q.D)

IT 20«s««A£ 1510

5 —

Y = 146.672 - 11.9510A + 0.2516A

R = 40.8% si = 0.02

12 14 16 18 20 22 24 26

Above-canopy radiation (MJ)26 30

FIGURE 4Effect of above-canopy (A) radiation at harvest (week 4) on2-methoxy-3-isobutylpyrazine concentration in Sauvignon

blanc grapes.

70

60

50

* 40

30

.*• 20

10

Y = 6.7709 + 1.5152A

R = 22.7% si = 0.046

12 14 16 18 20 22 24 26 28

Above-canopy radiation (MJ)30

FIGURESEffect of above-canopy (A) radiation at harvest (week 4)

on fruitiness intensity of Sauvignon blanc wine.

100

80

60

S."iS5 40

Y = 313.451 - 22.3616A + 0.4499A

R = 65.0% si < 0.01

12 14 28 3016 18 20 22 24 26

Above-canopy radiation (MJ)

FIGURE 6Effect of above-canopy (A) radiation at harvest (week 4) on

vegetative/asparagus/green pepper intensity of Sauvignonblanc wine.

fruitiness intensity and vegetative/asparagus/green pepper inten-sity showed a significant response to the above-canopy radiationonly (Figs. 4, 5 and 6, respectively). Again the vegetative/aspara-gus/green pepper intensity variation was best explained by a qua-dratic response of above-canopy radiation with 65.0%, and a min-imum turning point of 24.9% for the above-canopy radiation. Inspite of the fact that only 18 data points were applied for ripeningweek four, results obtained for vegetative/asparagus/green pepperintensity (65.0%, Table 2) were close to those of the full data set(68.8%, Table 1).

CONCLUSIONSThere is a significant relationship between gas chromatographi-cally-analysed grape aroma components, sensorially-evaluatedwine quality parameters and microclimatic data. Models are pre-sented, one of which can predict Sauvignon blanc wine quality(cultivar-typical vegetative/asparagus/green pepper intensity ^from above- and within-canopy radiation data, collected oveigrape ripening, with a fairly high degree of accuracy. It is there-fore possible to predict wine quality from easily-measurabhmicroclimatic data. The results of this investigation wert


26 A Model for Predicting Sauvignon blanc Wine Quality

obtained under specific South African conditions and it is notclaimed that they are valid under all conditions. Nevertheless,they can be considered as a contribution towards wine qualityprediction. Future research is necessary to test and refine thismodel for application under different environmental conditions.

LITERATURE CITED

Archer, E. & Strauss, H.C., 1989. Effect of shading on the performance of Vitisvinifera L. cv. Cabernet Sauvignon. S. Afr. J. Enol. Vitic. 10, 74-76.

Blackburn, W.J. & Proctor, J.T.A., 1983. Technical note. Estimating photosynthet-ically active radiation from measured solar irradiance. Solar Energy 31, 233-234.

Du Plessis, C.S. & Van Rooyen, P.C., 1982. Grape maturity and wine quality. S.Afr. J. Enol. Vrtic. 3, 41-45.

Francis, I.L., Hand, P.G., Cynkar, W.U., Kwiatkowski, M., Williams, P.J.,Armstrong, H., Bolting, D.G., Gawd, R. & Ryan, C., 1998. Assessing wine qualitywith the G-G assay. In: Blair, R.J., Sas, A.N., Hayes, P.p. & Hoj, P.B., (eds.). Proc.10th Aust. Wine Ind. Tech. Conf., 2-5 August 1998, Sydney, Australia, pp. 104-108.

Goudriaan, J., 1986. A simple and fast numerical method for the computation ofdaily totals of crop photosynthesis. Agric. For. Meteorol. 38, 249-254.

Haasbroek, P.D., Myburgh, J. & Hunter, J.J., 1997. Modelling sunlight intercep-tion and photosynthetic activity - correlation with field data. Poster. 21SI AnnualSASEV Congress, 27-28 November 1997, Cape Town, South Africa.

Holgate, A., 2000. Berry colour index assay - application and interprelation of theassay 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,Melbourne, Australia. In press.

Le Roux, E.G., 1974. 'n Klimaatsindeling van die Suidwes-Kaaplandse wyn-bougebiede. M.Sc. Thesis, University of Stellenbosch, StelSenbosch, South Africa.

Marais, J., Hunter, J.J. & Haasbroek, P.D., 1999. Effect of canopy microclimate,season and region on Sauvignon blanc grape composition and wine quality. S. Afr.J. Enol. Vitic. 20, 19-30.

Marais, J., Hunter, J.J., Haasbroek, P.D. & Augustyn, O.P.H., 1996. Effect ofcanopy microclimate on Sauvignon blanc grape composition. In: Slockley, C.S.,Sas, A.N., Johnstone, R.S. & Lee, T.H. (eds.). Proc. 9th Aust. Wine Ind. Tech.Conf., 16-19 July 1995, Adelaide, Australia, pp. 72-77.

Noble, A.C., Elliot-Fisk, D.L., & Alien, M.S., 1995. Vegetative flavor andmethoxypyrazines in Cabernet Sauvignon. In: Roussef, R.L. & Leahy, M.M.(eds.). Fruit flavors. Biogenesis, Characterization and Authentication. ACSSymposium. Series 596,22-27 August 1993, Chicago, Illinois, USA. pp. 226-234.

SAS. 1990. SAS/Stat User's Guide. Version 6, 4lh Edition, Vol. 2, SAS InstituteInc., SAS Campus Drive, Cary, NC 27513.

Spitters, C.J.T., 1986. Separating the diffuse and direct component of global radi-ation and its implications for modelling canopy photosynthesis. Part II,Calculation of canopy photosynthesis. Agric. For. Meteorol. 38, 231-242.


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