IRRIGATION OF FRUIT TREES AND VINES

J. Girona Æ M. Mata Æ J. del Campo Æ A. ArbonesE. Bartra Æ J. Marsal

The use of midday leaf water potential for scheduling deficit irrigationin vineyards

Published online: 14 October 2005� Springer-Verlag 2005

Abstract Midday leaf water potential (Ymd) was moni-tored for 3 years at a commercial vineyard (cv. PinotNoir) under four irrigation strategies. Three treatmentswere established based on irrigating vines with 4–6 mm/day, when daily measured Ymd was more negative thanthe pre-defined threshold. After the first experimentalyear, thresholds were adjusted for each treatment as: (1)Control (C), irrigated when Ymd was less than�0.6 MPaat the beginning of the season and gradually fell to�0.8 MPa at about mid-June, after which the thresholdwas maintained at �0.8 MPa until harvest. (2) Control–Deficit (CD), irrigated as C from bud-break to mid-June(around the middle of Stage II of fruit growth), and fromthen until harvest when Ymd decreased below �1.2 MPa.(3) Deficit–Deficit (DD), irrigated when Ymd was lessthan�1.0 from bud break to mid-May (about the middleof fruit growth Stage I), and after that time the Ymd

threshold became �1.2 MPa until harvest. A fourthtreatment was applied following a soil water budget ap-proach (WB). All treatments were replicated five timesbut irrigation in the Ymd-based treatments were inde-pendently applied to each of the replicate plots, whereasirrigation for WB was applied equally to all replications.The more site-specific information obtained from Ymd

thresholds in C provided substantial advantages for yieldhomogeneity and repeatability of results with respect toWB, thus demonstrating the method’s greater ability toaccount for spatial variability. Average applied water forthe 3 years in C, CD, and DDwas 374, 250, and 178 mm,respectively, while the yields were 11.8, 9.2, and 6.1 kg/vine, respectively. The CD treatment produced better

juice quality than C, and was superior in other qualityparameters to both C and DD. However, over the studyperiod, an important carryover effect was observed in theyields and the grape size of CD, which tended to diminishfrom year to year relative to C.

Introduction

In many dry lands of the Mediterranean arc, vines forwine production are grown without the support of irri-gation. Under such conditions, irrigation has two verydifferent effects: on one hand, relatively small watersupplements can remarkably increase grape production(Matthews and Anderson 1989; Reynolds and Naylor1994; Ferreyra et al. 2003; dos Santos et al. 2003), but onthe other, it is widely believed that wine quality may bereduced as grape size increases. As a result, full irrigationrequirements are seldom applied by wine grape growers(Peacock et al. 1998; Williams and Matthews 1990).

The most common vineyard irrigation practiceadvocates the application of nearly full irrigationrequirements during the early part of berry developmentand managing the water deficit during the final phases ofdevelopment (Williams and Matthews 1990). This is avery common practice under Mediterranean conditions.Another approach, mostly developed in Australia, rec-ommends an almost opposite strategy of applying lesswater early in the season, and irrigating to full crop waterrequirements during the latter phases of development(McCarthy et al. 2000). Although at first sight these twostrategies would seem to produce opposite effects on vineproduction, they have both shown to benefit wine pro-duction. In the first case this is achieved by reducinggrape size by limiting water accumulation, and in thesecond by limiting potential grape growth. The ultimatebenefit is to increase the proportion of skin to grape juiceand thereby improve wine colour (Williams et al. 1994).The suitability of using one of the strategies or the otherwould depend on the opportunities for applying the

Communicated by E. Fereres

J. Girona (&) Æ M. Mata Æ J. del Campo Æ A. Arbones Æ J. MarsalInstitut de Recerca i Tecnologia Agroalimentaries (IRTA),Area de Tecnologia Frutıcola, Centre UdL-IRTA,Rovira Roure 177, 25198 Lleida, SpainE-mail: joan.girona@irta.es

E. BartraInstitut Catala de la Vinya i el Vi (INCAVI), Estacio Enologica,Vilafranca del Penedes, Barcelona, Spain

Irrig Sci (2006) 24: 115–127DOI 10.1007/s00271-005-0015-7

water deficit. There are cases in which it is difficult toimpose intense water deficits during the early stages andthe stress must develop in the summer.

The water balance method (Allen et al. 1998) is theestablished technique for estimating full irrigationrequirements when crop coefficients are well adjustedand the reference evapotranspiration (ETo) informationis available. However, when dealing with deficit irriga-tion, imposing a deficit based on a water balance conceptimplies defining plant water stress on the basis of frac-tions of ET. This may produce a large degree of uncer-tainty as plant water stress development depends notonly on the fraction of water consumption replaced tothe soil, but also on soil water holding capacity, climateand plant material, and growing conditions (Reynoldsand Naylor 1994). Therefore, it is important to developdeficit irrigation strategies that can cope with the diffi-culties mentioned above, and which can be successfullyapplied and replicated. One alternative approach tousing fractions of the consumptive use requirements isby directly using plant water stress as an irrigationtrigger. In the past, attempts have been made to developsimilar systems based on diurnal trunk fluctuations(Pelloux 1990). More recently, experiments carried outon peach (Besset et al. 2001) and almond (Goldhamerand Fereres 2003), and using tentative threshold valuesof plant parameters as irrigation triggers, have provedthe feasibility of such an approach. Even so, usingdiurnal fluctuations in trunk diameter as an indicator oftree water status does not produce information with aseasonally stable significance (Marsal et al. 2002), andthe use of thresholds to establish irrigation requirementsneeds further phenological adjustments. For this reason,other more seasonally stable indicators may be pre-ferred, even though their measurements cannot be easilyautomated. A number of studies involving vine re-sponses to water have established general values of leafwater potential under adequate water status (Williamsand Araujo 2002; Grimes and Williams 1990; Ojedaet al. 2002). However, very seldom have studies involv-ing vine irrigation used such leaf water potentialthresholds as the only irrigation triggers.

The objectives of this study are: (1) to evaluate andadjust a methodology for scheduling vineyard irrigationbased on using midday leaf water potential thresholds asa stress indicator for triggering irrigation, and (2) todevelop a deficit irrigation strategy for wine grapes thatachieves a compromise between irrigation, yield, andquality.

Materials and methods

Experimental site

The experiment was conducted over three consecu-tive years (2001–2003) at a commercial vineyard(Vitis vinifera L.) of 12-year-old ‘‘Pinot-Noir’’ vines(1.7·3.10 m spacing) (1,900 vines/ha) located at Raımat,

Lleida (Spain). Soil texture was silty-loam and effectiveroot depth was about 90–110 cm. Average annualrainfall and ETo for this period were 440 and 873 mm,respectively. Rainfall was low in 2001 and 2002 with 379and 340 mm, respectively, and relatively high in 2003with 601 mm, though much of the rainfall in 2003 oc-curred after harvest. ETo remained relatively constantfrom year to year. Daily maximum temperatures wereabout 36–38�C.

Vines were trained to a lateral cordon system at aheight of 90 cm. Canopy management practices includedvertical shoot positioning in the month of June, andmechanical shoot topping shortly thereafter. Winterpruning was based on leaving ten to fifteen spurs pervine. A full cover herbicide program was appliedthroughout the growing season.

Irrigation water was supplied through a drip irriga-tion system with two 2.3 l/h drippers per vine positionedat regular intervals along the pipe. The system wasoperated by an irrigation controller that individuallyopened and closed the solenoid valves corresponding toeach experimental unit. Irrigation was scheduled on adaily basis immediately after the physiological mea-surements.

Leaf water potential thresholds

Ymd thresholds were defined bearing in mind valuesprovided by Grimes and Williams (1990); Peacock et al.(1998); Chone et al. (2001); and Williams and Araujo(2002). Generally speaking, –1.0 MPa was the preferredvalue at which to initiate irrigation in California, and�1.5 or �1.6 MPa were the lowest values achieved un-der dry conditions. According to the most recent liter-ature, a reasonable value for a well-irrigated vine wouldbe around �0.8 MPa. Therefore, we initially assumed athreshold of �0.8 MPa for well-irrigated vines,�1.2 MPa for moderately stressed vines, and �1.5 forsevere stress conditions. Nevertheless, we suspected thatseason-steady thresholds were perhaps inadequate forearly spring, as the phenological effects in developingleaves are very common early in the season (Marsal andGirona 1997). As a matter of fact, before May 2001, itwas observed that when using �0.8 MPa as a triggeringvalue, less water was applied and less shoot growth wasachieved than on similar plots where water balanceirrigation was applied. This difference provided evidencethat early Ymd thresholds would need correcting if theywere to serve as indicators for water stress.

The methodology used to find new thresholds early inthe season is based on maintaining fixed values of leafturgor pressure at midday, and is explained as follows.In 2001, Pressure–Volume curves, P–V, were determinedon a weekly basis for six leaves from C vines. This wasdone over the period from April until mid-June, whichcorresponded to the main phase of shoot development.P–V curves were generated applying a type II transfor-mation [1/Y plotted versus relative water content (R),

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where R=(fresh mass–dry mass)/(saturated fresh mass–dry mass)] (Tyree and Richter 1981), and using the freetranspiration method with a pressure chamber (Hinckleyet al. 1980). Turgid fresh weight (TW) was calculated asper Kubiske and Abrams (1990) by linear regression ofdata between balance pressure and sample fresh weightthat was clearly above turgor loss point, and extrapo-lating the line until Y=0. A more detailed description ofthe methodology used is presented in Marsal and Girona(1997). P–V curves were transformed into plots relatingleaf turgor pressure to leaf water potential, while thepercentage of turgor pressure—expressed in terms of fullturgor—needed to maintain Ymd equal to �0.8 MPawas first calculated from mid-June, when the majority ofleaves in the plant seemed to be mature. It was observedthat 50% of full leaf turgor pressure was required tomaintain a Ymd of �0.8 MPa, and that this percentagedid not vary between May and mid-June. It was there-fore assumed that the �0.8 MPa threshold was probablyappropriate from May onwards, and that 50% of fullturgor pressure could be used as a criterion for devel-oping new Ymd thresholds for the period before May.This meant that a well-irrigated vine would have a Ymd

that produced at least 50% of full leaf turgor pressure.On the basis of this criterion, 50% of full turgor valueswere recalculated on a weekly basis until May, therebyproviding new thresholds that increased in linear pro-portion with time from �0.6 MPa, at the beginning ofthe irrigation season, until they reached �0.8 MPa inMay.

Irrigation treatments

Three irrigation treatments were applied based on vinewater status strategies. The treatments were designed toirrigate 4–6 mm/day when daily measured midday leafwater potential (Ymd) was more negative than theestablished threshold defined for each treatment: (1)Control (C) irrigated when Ymd was less than �0.8 MPafor the full season during the first experimental year(2001), and during subsequent experimental years whenYmd was less than �0.6 MPa at the beginning of theseason, and gradually decreased to �0.8 MPa, and frommid June (about the middle of fruit growth stage II)until harvest, the threshold was maintained at�0.8 MPa; (2) Control–Deficit (CD) irrigated as C frombud-break to mid-June (about the middle of fruit growthstage II), and from mid-June to harvest when Ymd waslower than �1.2 MPa; and (3) Deficit–Deficit (DD)irrigated during the first year of experiment (2001) whenYmd was more negative than �1.5 MPa from bud-breakto mid-June, and when Ymd was more negative than�1.2 MPa from mid-June to harvest. During subsequentyears, DD vines were irrigated when Ymd was less than�1.0 from bud break to mid-May (about the middle offruit growth stage I) and from then until harvest when itwas less than �1.2 MPa. Irrigation treatments wereapplied to each of the replicate plots based on their

individual Ymd readings, which implied that not all thereplicates of a given treatment were necessarily irrigatedon the same day. After harvest, all the vines in alltreatments were irrigated until early October, followingthe same guidelines (Fig. 1).

To analyse spatial variability, an additional treatmentwas established based on the water budget (WB) ap-proach, following the guidelines of Goldhamer andSnyder (1989). Reference evapotranspiration (ETo) wascalculated using the Penman–Monteith equation (Allenet al. 1998) and data from a weather station 1 km fromthe experimental site (Generalitat de Catalunya 1994),and crop coefficients (Kc) were adapted from Williamset al. (2003).

The experimental layout was a randomized complete-block design with five block-replicates per treatment.Each of the 20 experimental plots consisted of fouradjacent rows of vines with twelve vines per row. Theeight central vines of the two central rows were moni-tored while the others served as guard vines. A total of960 vines were involved in this experiment, 320 of whichwere monitored.

Measurements

Midday leaf water potential (Ymd) was measured with apressure chamber (Scholander et al. 1965) (Soil Mois-ture plant water status console 3005 Corp. Sta. Barbara,CA, USA) following Turner and Long (1980) andMatthews et al. (1987). All measurements were done inless than an hour, and two leaves were measured perexperimental unit (one from each row). A total of 90measured-days per year were recorded for each experi-mental plot.

Light interception (LI) was determined as an indica-tor of vegetative development using a ceptometer (Ac-cupar, Decagon Devices Inc., Pullman, WA, USA).Data were gathered on a 12-point grid measured atground level. Each grid was located in the central por-tion of the individual plot and contained no bordervines. Incident radiation readings were taken above thevines. Light measurements were taken at midday atintervals of less than 1.5 h in mid-July, once a year.

Berry growth was determined on a weekly basis bysampling 16 berries per experimental plot (one berry pervine). Berry samples were taken to the laboratory andweighed to determine average fresh berry weight. Thetwo main diameters of each berry were then measuredusing a digital caliper, and the berries were oven dried at65�C to determine average berry dry weight.

Applied irrigation water was determined by readingthe water meters on each experimental plot on a dailybasis. This was done in order to verify that the quantitiesof irrigation water applied were as defined.

Irrigation scheduling was carried out on a daily basisimmediately after the daily averages in Ymd for eachexperimental unit were determined. Individual plotswhere Ymd was below the established thresholds were

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irrigated with 4–6 mm/day (4 mm from the beginning ofthe season until June, and 6 mm thereafter until harvest).

Fruit composition

A large fruit sample (about 200 berries per plot) wastaken at four different times from veraison to harvest todetermine quality parameters. Fruit soluble solids(�Brix) (FSS), pH, titratable acidity (TA), Anthocyanins,and total Polyphenols were determined for each sample,following the standard methodology (OIV 1990; Ilandet al. 1993; MAPA 1993).

Harvest was carried out on August 27th, 28th, and21st in the first, second, and third experimental years,respectively. Experimental vines were hand harvested,clusters for each vine were counted, and total vine yieldwas weighed. A sample of 100 berries per plot was takento the laboratory to perform the measurements forweekly berry growth described previously.

Results

Seasonal evaporative demand was quite similar fromyear to year (Table 1). Rainfall was only relativelyimportant during the vegetative phase and post-harvest.During the latter, rainfall accounted for an average of68% of total ETo, whereas from initial berry growthuntil harvest, it only represented 20% of total ETo

(Table 1).

Midday leaf water potential (Ymd) used as a thresh-old for irrigation scheduling revealed clear differences inYmd average values for each irrigation treatment(Fig. 2). In the early part of the season and until June, itwas rare to find Ymd values below the thresholds for Cand CD vines (Fig. 2a). As a result, little water wasapplied to the C and CD treatments. For the sameperiod, DD only exceeded the threshold value (�1 MPa)for 7 days, whereas irrigation was not necessary for therest of the period. Although treatment differences wereminor, the cumulative applied water for C was differentthan that of both CD and DD, with each having dif-ferent thresholds for the period in question (Fig. 3).From June until harvest, Ymd of C was below thethreshold for irrigation (�0.8 MPa) for about 80% ofthe measured days, with a resulting increase in irrigationrates during this period (Fig. 3). In DD, when thethreshold was reduced by 0.2 MPa at the end of May, aperiod of 2 weeks was necessary before Ymd approachedthe new threshold values. In the CD treatment, thethreshold change was applied at the end of June, and thesudden decrease in 0.4 MPa implied withholding irri-gation for a period of about 3 weeks, during which Ymd

values progressively decreased until the new thresholdwas achieved. After these adjustments, Ymd for thedeficit treatments (CD and DD) oscillated around thetarget value, with the exception of a few sudden spikesthat were related to rainfall (Fig. 2). Average middayleaf water potential for each phase in the annual cyclealso showed clear differences between treatments, and

Fig. 1 Irrigation treatment (C control, CD control-deficit, DD deficit-deficit) definitions based on threshold values for midday leaf waterpotential. [C01, thresholds applied during the first year of the experiment (2001), C02&03, thresholds applied during the second and thirdyears of the experiment (2002 and 2003)]

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these were repeated with the same tendencies for thedifferent years of the experiment (Table 2).

The amounts of water applied during the first year ofthe experiment were 378, 252, and 148 mm for C, CDand DD, respectively (Fig. 3). These amounts seemed to

be frequently repeated over the 3 years of the experi-ment, except for the DD treatment in which annualirrigation approached 190 mm after the first year, asopposed to the 148 mm of the first year. This differencein applied water in DD was due to the change inthreshold for the early part of the season when it wasraised from �1.5 to �1.0 MPa for the last 2 years, be-cause �1.5 MPa restricted excessively irrigation early inthe season, to the point that hardly any was applied untilearly June (Fig. 3).

Canopy light interception measured once vegetativedevelopment had ended indicated that vines receivingCD irrigation did not experience significant reductionsin their values in comparison with C vines in any of thethree experimental years (Table 3). However, vines fromDD had significant reductions in canopy light intercep-tion over the 3 years (Table 3).

The effects of year (year) and irrigation treatment(TRT) on vine yield were highly significant (Table 4).The interaction of TRT · year was also significant

Fig. 2 Seasonal patterns ofmidday leaf water potential in2002 with the indications of thepre-defined thresholds for eachirrigation treatment. Each pointrepresents the average of 10measurements (five replications,with two measurements perreplicate plot)

Table 1 ETo and rainfall for the different phases of the annualcycle during the 3 year experiment

Weather water balance (mm)

Year Vegetativephase

Initial berrygrowth

Veraison toharvest

Post-harvest

2001ETo 203.5 208.0 191.1 139.5Rain 81.7 54.9 58.3 55.22002ETo 188.7 217.7 191.3 135.1Rain 90.6 45.3 28.7 82.82003ETo 170.5 223.4 213.2 117.7Rain 92.9 23.7 50.0 193.5

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(Table 4). The reason for this significant interaction isrelated to the progressive changes that were mainly ob-served in the CD vines: they showed no significant dif-ferences for the first year (Table 5), a significant yieldreduction for the second year (yield being 81% of C),and an even more significant reduction in the third year(yield being 76% of C) (Table 5). The Year effect onyield components was significant at all levels [Clustersper vine (NCV), berries per cluster (NBC), average berryfresh weight (ABFW)] (Table 4). However, the effect ofdeficit irrigation on yield components was only seen insignificant reductions in ABFW and NCV, while NBCremained unaffected. Analysing yield behaviour by year,irrigation treatments effect was only slightly significantfor the first year, when only the DD were significantlylower than those from C vines. The effects of the irri-

gation treatments became progressively more significantas time went on, and in the third year, CD yields weresignificantly lower than those of C, while DD yields werealways significantly lower than those of C and CD vines(Table 5). In the first year, the only yield componentaffected by irrigation was ABFW, DD vines havinglower ABFW than C vines. In the second year, CD alsohad significantly lower ABFW than C. During the thirdyear, reductions in irrigation for DD were also reflectedin significant reductions in NCV.

Berry growth was affected in the deficit-irrigatedvines (Fig. 4). In the early stages (June), DD berries hadless fresh weight than C and CD berries (Fig. 4). Later,from early July onwards, once the CD threshold wasreduced to �1.2 MPa, berry fresh weight in CD de-creased consistently in comparison with C vines (Fig. 4).

Fig. 3 Seasonal patterns ofcumulative applied water foreach irrigation treatment (Ccontrol, CD control-deficit, DDdeficit-deficit) and for the 3 yearsof the experiment [C-01: first year(2001), C-02: second year (2003),and C-03: third year (2003)].Each point represents the averageof five replications

Table 2 Average values for midday leaf water potential for each irrigation treatment at different phases of the annual cycle during the3 year experiment

Year Irrigation treatment Midday leaf water potential (MPa)

Vegetative phase Initial berry growth Veraison to harvest Post-harvest

Average ±ES Average ±ES Average ±ES Average ±ES

2001 C �0.85 0.007 �0.91 0.005 �0.88 0.008 -0.90 0.016CD �0.80 0.012 �0.93 0.010 �1.04 0.009 �1.00 0.014DD �0.92 0.007 �1.17 0.005 �1.15 0.006 �1.07 0.009

2002 C �0.72 0.015 �0.83 0.009 �0.88 0.006 �0.85 0.020CD �0.78 0.014 �0.82 0.006 �1.10 0.005 �0.94 0.029DD �0.92 0.010 �1.07 0.004 �1.17 0.003 �0.92 0.004

2003 C �0.62 0.003 �0.89 0.006 �1.03 0.007CD �0.62 0.007 �0.84 0.014 �1.21 0.007DD �0.73 0.007 �1.14 0.006 �1.28 0.005

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These patterns were consistently repeated over the threeexperimental years. Dry weight accumulation in berrieswas also reduced in line with the reduction in the Ymd

threshold for irrigation, although to a lesser extent thanfresh weight. At harvest, differences in berry dry matteramong irrigation treatments were not significant (datanot shown).

The quality of grape juice during the last weeks be-fore harvest was affected by the irrigation treatments;grapes from all treatments experienced steady increasesin �Brix from 4 weeks before harvest, and those fromDD presented higher �Brix values than the other twotreatments for the first sample day (Fig. 5a). These dif-ferences were maintained for almost all the days andyears sampled (Fig. 5a). Hardly any significant differ-ence was observed between C and CD (Fig. 5a). Similardifferences were observed for titratable acidity duringpre-harvest; DD always presented lower values than Cand CD (Fig. 5b). In relation to juice pH, CD was the

treatment that presented the lowest values during pre-harvest with hardly any observed differences between Cand DD (Fig. 5c). Such differences were drastically re-duced at harvest (Table 6). The tendencies observedduring pre-harvest in the different treatments for solublesolids and acidity tended to be maintained at harvest(Table 6).

The comparison between the two irrigation-schedul-ing methods presented in Table 7 indicate that the use ofYmd thresholds in C vines (each elemental plot irrigatedindependently) reduced fourfold the variability amongindividual plots (expressed in terms of their annualaverage Ymd), relative to the situation where a waterbalance method was used for scheduling. In the WBtreatment, all elemental plots were irrigated with thesame amount of water (Table 7). Likewise, yield andBFW exhibited less variability (CV=4.7 and 3.2%,respectively) in C than in WB (CV=8.2 and 8.5%,respectively) (Table 7).

Table 4 Effects of irrigation treatments on fresh yield and yield components for the experimental period 2001–2003

df Variables

Yield NCV ACW ABFW NBC NBV

Signification (Pr > F)Model 20TRT 2 <.0001 0.0021 <.0001 <.0001 0.7310 0.0025Year 2 0.0002 <.0001 <.0001 <.0001 <.0001 <.0001REP 4 0.2002 0.5733 0.0008 0.1110 0.0030 0.0780REP*Year 8 0.2238 0.2917 0.4864 0.9883 0.9833 0.4021TRT*Year 4 0.0159 0.3454 0.0061 0.1082 0.8712 0.7182Error 24

Irrigation TRT (Mean separation)C 10.82 a 98.2 a 109.6 a 1.35 a 81.6 8162 aCD 9.21 b 96.4 a 96.3 b 1.17 b 83.2 8151 aDD 6.12 c 81.2 b 75.0 c 0.93 c 80.9 6693 b

Means within column/year followed by different letters were significantly different at P=0.05 using Duncan’s test. TRT Irrigationtreatments. Yield kg per vine in fresh weight. NCV number of clusters per vine. ACW average cluster weight (g). ABFW average berryfresh weight (g). NBC number of berries per cluster NBV number of berries per vine

Table 3 Effects of irrigation treatments on vine light interception, at about the end of July, for each year of the experiment

df Years (date)

12 July 2001 29 July 2002 25 July 2003

Signification (Pr > F)Model 6TRT 2 0.0019 <.0001 0.0225REP 4 0.0168 0.0023 0.0783Error 14

Irrigation TRT (Mean separation)C 56.9 a 48.0 a 42.5 aCD 52.4 a 47.1 a 41.7 aDD 41.4 b 33.2 b 34.8 b

Means within column/year followed by different letters were significantly different at P=0.05 using Duncan’s test. TRT Irrigationtreatments. For each elemental plot 12 radiometer measurements were taken under the vines and two were taken over the vines asreferences for light interception

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Discussion

Berry size and water content are two of the main factorsaffecting berry growth and wine quality that are influ-enced by irrigation. In this study, the degree of waterstress strongly influenced berry growth in fresh (Fig. 4)and dry weight. DD vines had the highest levels of waterstress and also the lowest rates of berry growth, while Cberries always grew fastest. Berries from CD vines onlygrew as fast as those in C during the first year of theexperiment (Fig. 4) as reported by other authors in 1-year studies (Reynolds and Naylor 1994; Ojeda et al.2002). However, it was clear from our study that the CDberries growth rates cannot be sustained over the years;in fact, carry over stress effects in CD were evident insubsequent years, when CD berries grew proportion-ately less than C (Fig. 4). This carry over effect was notlikely to be explained by an increase in fruit load, be-cause crop light interception in CD was not significantlydifferent from that of C, and the number of clusters pervine also remained unchanged. Similarly, it was not

likely that the carry over effect was related to anincreasing water deficit during veraison as years went on,because the average Ymd difference between C and CDwas of similar magnitude in the first and in the thirdyears (0.16 and 0.17 MPa, respectively; Table 2). Itcould therefore be argued that the carbon reservoir wasprogressively depleted in CD, and that this hypotheticalcarbon limitation reduced the potential for berrygrowth. These long-term effects on fruit growth havebeen observed in RDI experiments with trees (Gironaet al. 2003, 2005), and has been associated with carbonstorage depletion in almond (Esparza et al. 2001). Inaddition, a recent study has suggested the same responsein vineyards under deficit irrigation (Ferreyra et al.2003). A reduction in reserves tends to reduce fruit sol-uble solids (FSS) as the experiment advances. Suchreductions were observed in CD berries, but becausethey were also accompanied by substantial increases inacidity, low FSS could just be indicative of a delay inripening (Table 6, Fig. 5). It has been shown that FSStends to increase over time, while acidity does theopposite (Matthews and Anderson 1988; Sipiora and

Table 5 Effects of irrigation treatments on fresh yield and yield components for each of the 3 years of the experiment

df Variables

Yield NCV ACW ABFW NBC NBV

Year 2001

Signification (Pr > F)Model 6TRT 2 0.0111 0.2054 0.0002 0.0047 0.7331 0.3036REP 4 0.0908 0.1489 0.0724 0.9966 0.4747 0.1445Error 8Irrigation TRT Mean separationC 6.73 a 69.0 97.0 a 1.38 a 71.4 5000CD 7.31 a 77.9 92.5 a 1.33 a 69.3 5475DD 4.28 b 65.4 64.7 b 0.97 b 66.7 4343

Year 2002

Signification (Pr > F)Model 6TRT 2 0.0010 0.0932 <.0001 <.0001 0.6903 0.0567REP 4 0.6708 0.7236 0.0093 0.3576 0.3767 0.6210Error 8Irrigation TRT Mean separationC 12.31 a 98.6 126.2 a 1.45 a 87.0 8532CD 10.01 b 89.9 111.6 b 1.24 b 90.0 8030DD 6.44 c 73.3 87.5 c 1.00 c 87.4 6423

Year 2003

Signification (Pr > F)Model 6TRT 2 0.0001 0.0349 <.0001 0.0003 0.7756 0.1110REP 4 0.0771 0.2503 0.0014 0.7891 0.5974 0.2678Error 8Irrigation TRT Mean separationC 13.43 a 127.0 a 105.6 a 1.23 a 86.3 10950CD 10.29 b 121.4 a 86.8 b 0.94 b 90.4 10948DD 7.66 c 105.0 b 72.9 c 0.82 b 88.7 9312

Means within column/year followed by different letters were significantly different at P=0.05 using Duncan’s test. TRT Irrigationtreatments. Yield kg per vine in fresh weight. NCV number of clusters per vine. ACW average cluster weight (g). ABFW average berryfresh weight (g). NBC number of berries per cluster NBV number of berries per vine

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Gutierrez-Granda 1998). Generally speaking, the CDirrigation regime improved berry quality, though themechanism responsible for this improvement remainedunclear, and the quality response varied from year toyear, i.e. sometimes anthocyanins were improved (2002),and other years’ total polyphenols were improved in CDrelative to C (2002 and 2003).

In the case of DD, berry quality generally improvedin all measured parameters relative to C berries.However, during the third year, this quality improve-ment was partially lost because the anthocyanin andtotal polyphenol values were not significantly higher

than those of C (Table 6, Fig. 5). There is no clearexplanation for this loss of quality, since the DD berrysize was reduced in 2003 to a similar extent as it hadbeen in 2001, and comparative treatment differences inYmd, were of a similar magnitude from one year toanother. However, during the initial vegetative phase in2003, differences in water stress levels between C andDD (Table 2) were substantially reduced, while vinedevelopment—as indicated by light interception, berrysize, and yield components—showed similar trendsover the 3 years (Table 3, Fig. 4, and Table 5). DDvines probably adapt to extended periods of water

Fig. 4 Seasonal patterns of berry fresh (a, c, e) and dry (b, d, f) weights for each irrigation treatment (C control, CD control–deficit, DDdeficit–deficit), and for each of the experimental years. Each point represents an average for 80 berries (16 berries per repetition, with fivereplications)

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stress, as it has been described for other vegetationtypes (Osmond et al. 1987), by modulating vegetativegrowth in response to early water stress, and thusachieving a new equilibrium between abovegroundbiomass and the root system. After 3 years of experi-ment, DD and CD vines had achieved a new level ofyield and canopy size. However, berry quality behaveddifferently and, by a hitherto undetermined mechanism,apparently returned to levels more akin to those of C.Perhaps the pattern of water stress also affects thelong-term responses in berry quality as it was lesssensitive in DD vines after a period of adaptation than

it was in CD vines. Along the same lines, it has beenreported that late stress is more effective for improvingwine quality (Matthews and Anderson 1988) than stressapplied earlier in the season, and that mild water stress,applied at specific phenological stages, is most effectivein improving quality (Bravdo and Naor 1996). Theseobservations could be relevant for some cultivars like‘‘Pinot Noir’’ in which quality is not only related to areduction in berry size but also to an increase inanthocyanin concentration in the berry epidermis(Matthews and Anderson 1988; Freeman and Kliewer1983; Williams and Matthews 1990).

Fig. 5 Seasonal patterns forfruit quality parameters(soluble solids, titratableacidity, and pH) during the lastweeks before harvest for eachirrigation treatment (C control,CD control–deficit, DD deficit–deficit) and for the 3 years ofthe experiment (ns nonsignificant, and *significant atP=0.05 irrigation treatmenteffects within each group)

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The substantial yield decline in DD vines (43%reduction on average over the 3 years) contrasted withthe slight reduction in CD vines (14.8%). While yielddecline was due to both a reduction in the number ofclusters per vine (third year) and in berry size for DD,the yield decrease in CD was mainly caused by reduc-tions in berry size. The fall in the number of clusters inDD can be explained by the influence of early waterstress on reducing vegetative growth, and consequentlyreducing the number of spurs per vine (fruiting posi-tions, data not shown) available the following year. Thetrend in yield decline size experienced by CD in succes-sive years was not observed in DD, where yield reduc-tions tended levelled off at around 45% of C from thesecond year. The relative advantages of using the twodeficit irrigation strategies should be assessed from thepoint of view of time and quality. DD strategies areassociated with a yield loss that can only be offset by aputative improvement in the quality of the wine pro-duced from DD grapes. It does not seem possible tomaintain high yields and reduce berry size at the sametime, but if there is a necessity to reduce irrigation, theCD treatment seems to provide the best irrigationstrategy. Yield reductions were much less than in DD,and the loss in yield was offset by the production ofsmaller berries, thus potentially improving wine quality.

Scheduling irrigation based on pre-established Ymd

thresholds gave consistent results for various aspects ofirrigation management: (1) in the different irrigation

treatments, applied water was clearly different as themagnitude of the thresholds varied, (2) different irriga-tion treatments produced clear differences in yield andquality, and (3) differences in applied water affectingyield were maintained throughout the 3 years of theexperiment. Other authors have reported on schedulingirrigation by means of plant water stress indicators usingcontinuous or discrete measurements (Goldhamer andFereres 2003; Ginestar et al. 1998; Li and Huguet 1989).However, the majority of these studies focused onevaluating the response in a single year or only at spe-cific times within a season.

The use of plant-based indicators to trigger irrigationhas an advantage over the water balance method in thatits indicators provide more site-specific information andcan thus account for spatial variations. When comparingthe use of the Ymdmethod for individual plots as opposedto a water balance technique, the Ymd method substan-tially reduced the variability in the annual average Ymd

(Table 7). This result was not necessarily expected, sincethe irrigation criterion was not to maintain Ymd at onespecific interval. As a matter of fact, Ymd values notablydeparted at times from the irrigation threshold during theseason (Fig. 2). However, it is important to underline thefourfold reduction in the coefficient of variation in Ymd

when using the Ymd versus the WB method, and therelated 2.6 and 1.7 fold reductions in the coefficients ofvariation for berry size and yield (Table 7). This dem-onstrates that scheduling irrigation according to the Ymd

Table 7 Applied water, leaf water potential, yield, and berry fresh weight for each replications-block and irrigation treatments C and WB

REP C WB

Irrigation (mm) Ymd (MPa) Yield (kg/vine) BFW (g) Irrigation (mm) Ymd (MPa) Yield (kg/vine) BFW (g)

I 364 -0.83 8.99 1.44 390 -0.95 9.62 1.40II 399 -0.84 9.49 1.34 393 -0.86 10.40 1.33III 370 -0.87 10.22 1.45 388 -0.80 11.56 1.63IV 397 -0.86 9.57 1.41 393 -0.93 10.47 1.34V 329 -0.87 9.35 1.44 393 -0.82 11.73 1.44CV 7.7% 1.9% 4.7% 3.2% 0.6% 7.6% 8.2% 8.5%

REP Repetition (blocks); Ymd Leaf water potential; BFW Berry fresh weight at harvestValues presented are the 2001 and 2002 averages within repetition block

Table 6 Effects of irrigation treatments on grape juice quality at harvest for each of the 3 years of the experiment

Year Quality parameters

Irrigation treatment Anthocyanins (mg/kg) Total polyphenols (mg/kg) pH Titratable acidity (g/l) Soluble solids (�Brix)

2001 C 406.4 b 15.7 b 3.9 ab 3.9 b 24.7 bCD 369.4 b 14.9 b 3.8 b 4.5 a 24.6 bDD 478.4 a 19.3 a 4.0 a 3.5 c 25.8 a

2002 C 619.6 b 12.9 b 3.6 5.8 a 21.5CD 782.1 a 16.4 a 3.5 5.8 a 20.0DD 806.4 a 16.5 a 3.6 5.0 b 22.0

2003 C 643.8 10.5 ab 3.6 4.5 b 20.7 abCD 725.4 11.9 a 3.6 5.0 a 19.8 bDD 694.4 9.8 b 3.7 4.3 b 21.2 a

Means within column/year followed by different letters were significantly different at P=0.05 using Duncan’s test

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method increases the precision of irrigation with highlyrepeatable results, and could potentially improve thehomogeneity of grape juice, a key factor in wine pro-duction. Note, however, that this methodology was ap-plied at an experimental scale where the individual plotswere less than 200 m2 and that two Ymd measurementswere taken for each plot. This implied a high sampleintensity with correspondingly high labour costs. It wouldtherefore be interesting to adapt this method to com-mercial size plots, and to determine the smallest Ymd

sample size required to manage the irrigation with thedegree of precision required for a given target.

Acknowledgements The authors would like to thank Raımat Win-eries, and particularly X. Farre and J. Esteve, for allowing to carryout this research on their vineyards, and for their keen interest inthe results. The authors would also like to thank D. Manresa forskilful technical assistance. Thanks are due to E. Fereres and D.Goldhamer for their contribution in the initial design of theexperiment, and to two anonymous reviewers for their commentsand suggestions for improving the manuscript. This research waspartially supported by INIA grant VIN00-17–C2.

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