Response of Vitis vinifera cv. ‘Tempranillo’ to partial rootzone drying in the field: Water relations, growth, yield and fruit and wine quality

agricultural water management 96 (2009) 282–292

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Response of Vitis vinifera cv. ‘Tempranillo’ to partial rootzone drying in the field: Water relations, growth, yield and fruit and wine quality D.S. Intrigliolo *, J.R. Castel Instituto Valenciano Investigaciones Agrarias (IVIA), Centro para el Desarrollo de Agricultura Sostenible, Apartado oficial 46113, Moncada, Valencia, Spain

article info

abstract

Article history:

This paper reports the effects of irrigation amount and partial rootzone drying (PRD) on

Received 27 May 2008

water relations, growth, yield and wine quality of Vitis vinifera cv. ‘Tempranillo’ during two

Accepted 3 August 2008

consecutive years in a commercial vineyard with a deep, light-clay soil located in Requena,

Published on line 11 September 2008

Valencia, Spain. Partial rootzone drying applied at two amounts (100% and 50% of the estimated crop evapotranspiration), was compared to conventional drip irrigation, and also

Keywords:

to rainfed vines. Results showed that the effects of irrigation amount on yield and wine

Crop load

quality were different between years. In 2003 with low yield values (around 6.3 t ha1)

Deficit irrigation

irrigation did neither affect grape production nor wine quality. However, in the following

Grapevine leaf and stem water

year, with much higher general yield (17 t ha1), the high irrigation dose increased yield by

potential

30% compared to rainfed vines and it also increased must total soluble solids and wine

Stomatal conductance

alcohol content. In both seasons, PRD did not significantly affect physiological parameters, nor growth, yield or fruit and wine quality, when compared to the same amount of water applied by conventional drip irrigation. Overall these results suggest that, under our experimental conditions, it was the irrigation amount rather than the system of application what affected vine performance, indicating the difficulties of successfully employing the PRD type of irrigation with a drip system in heavy and deep soils. # 2008 Elsevier B.V. All rights reserved.

1.

Introduction

Soil water availability is a critical factor for vine performance and wine composition. Irrigation allows increasing yields (Williams and Matthews, 1990), though a moderate water deficit is often desirable to improve wine composition (Jackson and Lombard, 1993). Deficit irrigation and ‘‘Partial Rootzone Drying’’ (PRD) (McCarthy et al., 2000) have been suggested as strategies to increase water use efficiency (weight of fruit produced per unit of irrigation water applied). The goal is also to improve fruit composition for premium quality wines by reducing canopy vigor, increasing fruit exposure to light and reducing berry growth to avoid dilution effects.

Deficit irrigation consists in reducing water application rates to replace only part of the potential vine evapotranspiration either during the whole season or only during certain phenological periods. Partial rootzone drying aims instead on alternating water application between the two sides of the vine in order to maintain part of the root system in contact with dry soil, while the rest of the rootzone is in a wet condition. The physiological mechanisms behind the PRD practice are based on studies with potted plants, where often roots were artificially separated in two containers (Antolı´n et al., 2006; Dry and Loveys, 1999; Stoll et al., 2000). These investigations showed that vines with half of the root system always in contact with dry soil had lower stomatal

* Corresponding author. Tel.: +34 963424000; fax: +34 963424001. E-mail address: [email protected] (D.S. Intrigliolo). 0378-3774/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.08.001

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agricultural water management 96 (2009) 282–292

Table 1 – Values of reference evapotranspiration (ETo) and rainfall during the growing season (April to harvest) and annual rainfall each year Year

2003 2004

Growing season ETo (mm)

Growing season rainfall (mm)

Annual rainfall (mm)

828 798

185 228

321 521

Irrigation (mm) NI

50

50-PRD

100

0 0

53 46

56 47

93 82

100-PRD 102 86

Irrigation volumes applied to the different treatments are also shown.

conductance and reduced vegetative growth, without detrimental effects on yield and improvement in fruit quality. In other research deficit irrigation under a PRD regime was compared to conventionally fully watered vines (Dry et al., 1996, 2000; Poni et al., 2007), with the absence of a proper control, e.g. deficit irrigation applied conventionally. Further research on PRD conducted in the field showed absence of any significant effect of PRD when it was compared with the same amount of water applied conventionally (Bravdo et al., 2004; Gu et al., 2004; Pudney and McCarthy, 2004). Particularly under heavy deep soils (Marsal et al., 2008) the PRD technique seems to be less effective than under sandy soil (de Souza et al., 2003), where wetting and drying cycles can be achieved more easily. Recently, De la Hera et al. (2006) found somewhat higher yield in PRD treatments compared with conventional drip irrigation in one out of the three seasons of their study. Pedreira dos Santos et al. (2007) reported better fruit exposure to light and improved fruit composition when PRD was compared with the same amount of water applied conventionally. Under these circumstances it was considered important to test the PRD practice in the field conditions of heavy and deep soils typical of the Utiel-Requena counties (Valencia, Spain). The aim of this work was then to evaluate the effects of the irrigation dose and of the system of application (conventional drip and PRD) on water relations, yield and wine quality of Tempranillo grapevines during two seasons. The ultimate goal is to provide growers with reliable information about the convenience of using the PRD drip-irrigation system in their vineyards.

2.

Materials and methods

2.1.

Site description

The experiment was carried out during two consecutive seasons (2003 and 2004) in a ‘Tempranillo’ vineyard (Vitis vinifera L.) planted in 1991 on 161-49 rootstock at a spacing of 2.45 m by 2.45 m (1666 vines ha1). The vineyard was located near Requena (398290 N, 18130 W, elevation 750 m), Valencia, Spain. In 2000, a drip-irrigation system was installed and vines trained to a vertical trellis on a bilateral cordon system oriented in the North–South direction. Shoot thinning was carried out each year according to the vineyard manager goals. This led to a different number of shoots retained, 8 and 16 in 2003 and 2004, respectively; and hence different numbers of clusters collected between years. All treatments were fertilized at a rate of 30-20-60-16 kg ha1 of N, P2O5, K2O, and Mg, respectively.

The soil at the site was a Typic Calciorthid, with a clay loam to light-clay texture, highly calcareous and of low fertility (0.66% of organic matter content, and 0.04% of total nitrogen). The soil has a deep soil profile (>2 m), available water capacity is about 200 mm m1 and bulk density 1.43–1.55 t m3. Budbreak for Tempranillo in this area usually occurs by mid April, flowering by early June; veraison is reached by earlyAugust with harvest during late September and leaf fall at the beginning of November. Climate is continental and semiarid with average annual rainfall of 430 mm of which about 65% falls during the dormant period. Weather conditions during the experiment (Table 1) were measured with an automated meteorological station located in the plot and reference evapotranspiration (ETo) was calculated with hourly values by the Penman-Monteith formula as in Allen et al. (1998).

2.2.

Irrigation treatments and experimental design

Treatments studied were (i) rainfed, with no irrigation (‘‘NI’’), (ii) ‘‘50’’, watered at 50% of estimated crop evapotranspiration (ETc) during the whole season, (iii) ‘‘50-PRD’’, irrigated at the same dose as ‘‘50’’ but with water that was applied on only one side of the vine at a time (PRD type of irrigation), (iv) ‘‘100’’ watered at 100% of ETc during the whole season, and (v) ‘‘100PRD’’, irrigated at 100% of ETc but with water application of PRD type. These irrigation treatments were chosen in order to test the effectiveness of the PRD type of irrigation under two watering regimes, full and deficit irrigation. Irrigation started on 19 June (day of the year (DOY), 170) and on 23 June DOY 173 in 2003 and 2004, respectively. Water applications ended in both years by the end of August. In the PRD treatments irrigation was initially applied in the north side of the vines during two weeks, after that, irrigation was switched to the south side of the vine, alternating water applications between both sides on a fortnightly basis. Each treatment had six replicates in a randomized complete block design. Each plot consisted of 10 rows with 9 vines per row and the surrounding perimeter vines used as buffers. Crop evapotranspiration was estimated as product of ETo and crop coefficient (Kc). Kc values used were 0.30 from flowering (early June) to veraison (end of July) and 0.15 from veraison to harvest (mid September). Water was applied with two pressure-compensated emitters of 2.4 L h1 located 60 cm on either side of the vine, on a single line per row for the conventional drip-irrigation treatments and on a double line per row for the PRD ones. Frequency of water applications was the same for all irrigated treatments and varied from 3 to 5 days per week. Water meters measured the amount applied to each irrigated replicate.

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2.3.

agricultural water management 96 (2009) 282–292

Field determinations

Soil water content (SWC) was continuously monitored at 10 cm intervals down to 160 cm, with a capacitance probe (Diviner, 2000, Sentek Pty., South Australia). Access tubes were only installed in the PRD irrigation regimes. Four tubes per treatment were placed in the row line approximately 75 cm from a vine trunk and about 25 cm from a dripper. An in situ calibration against volumetric soil moisture was previously performed by collecting undisturbed soil samples from each depth down to 100 cm in tubes installed for that exclusive purpose. Access tubes were located on both sides of the vine (2 tubes on each side). Soil moisture content readings were taken every two weeks coinciding with the alternating water application regimes of the PRD treatments. Determinations of plant water potential were performed with a pressure chamber (Soil Moisture Corp., Santa Barbara, USA) on five representative plants per treatment and two leaves per vine, at early morning (07:00–08:00 h solar) and at midday (11:30–12:30 h solar) on bag covered leaves (stem water potential, cs) at fortnightly intervals. At midday leaf water potential determinations (cl) were also performed. Determinations at predawn (before 05:00 h, cpd) were also carried out on a monthly interval. Stomatal conductance (gs) was measured around solar midday using a dynamic diffusion porometer (AP4, Delta-T Devices, Cambridge, UK) on the same vines used for c measurements and three fully expanded, sun-exposed leaves per vine. Seasonal variation of berry fresh weight was determined by collecting samples of 100 berries per each experimental plot (6 replicates per treatment) at 10 days intervals. Yield was determined at harvest on each of the 7 internal rows (7 vines per row) of each replicate. The number of clusters per vine was determined in 12 vines per plot and average cluster weight determined from randomly selected samples of at least 20 clusters per plot. Final berry weight was determined on random samples of about 200 berries per replicate. Pruning weight (PW) and leaf area (LA) were determined in four vines per replicate. Leaf area was estimated after veraison when shoot growth had ceased. Leaf area per vine was estimated from a linear equation relating leaf area (Y, cm2 per shoot) and total (main plus laterals) shoot length (X, cm). This relationship was obtained from samples of about 10–20 representative shoots of different lengths collected after veraison each year. Thus, leaf area per vine was calculated from the sum of each of the measured individual shoot lengths. Leaf area to yield ratio (LA/Y) and yield to pruning weight ratio (Y/PW) were also calculated in the four selected vines per replicate.

2.4.

Must and wine quality determinations

Must components were determined in the same samples collected for berry fresh weight determination, which were crushed with a small hand-press, and the juice centrifuged. Total soluble solids (Brix) were determined by refractometry. Juice pH and titratable acidity (TA) were determined by an automatic titrator. Organic acids (malic and tartaric

in juice and wines and lactic only in wines) were analyzed by high-performance liquid chromatography following procedures described by Romero et al. (1993). Ethanol in the wines was analyzed by gas chromatography. Wine color intensity (OD420 + OD520 + OD620), and total phenolics index (OD280) were determined by spectrophotometry in accordance with Ribereau-Gayon et al. (2000) and they were expressed in terms of absorbance units (AU). Anthocyanins (OD520 in HCl media) were also determined by spectrophotometry. All analytical determinations were duplicated.

2.5.

Microvinifications procedure

Grapes from the different treatments were harvested on the same day (or with one day difference) and a single set of vinifications was performed. In 2004 two sets of vinifications were carried out by harvesting half of the experimental vines on 22 September, while the rest were harvested later, on 4 October. Vinifications were performed separately on samples of about 30 kg per replicate, most often six per treatment. Grapes were mechanically crushed, de-stemmed, and fermented at about 25 8C in stainless steel containers. All wine lots were inoculated with a commercial yeast strain (L-2056, Danstar Ferment AC, Zug Switzerland) at 100 mg kg1. Skin contact time was seven days and during this time they were punched down automatically every four hours. After alcoholic fermentation they were racked off and malolactic bacteria (Oenococcus oeni) inoculated. They were again racked off, sulfited at 100 mg L1 K2S2O5, decanted and bottled. Analytical determinations in the wines were performed at the same time in both years just before inoculation with malolactic bacteria and about one month after grapes were crushed.

2.6.

Statistical analysis

Analysis of variance was performed using the GLM procedures of the SAS statistical package (version 8.2; SAS Institute, Cary, NC). Differences between treatment means were assessed by Dunnett’s t test against the non-irrigated (control) and by means of designed contrasts between pair of treatments.

3.

Results

3.1.

Climatic conditions and soil and plant water relations

Season 2003 was drier than the 2004 one with lower annual rainfall and also lower precipitation during the growing season (Table 1). Evaporative demand during the growing season was similar for both years. The evolution of soil water content in the PRD treatments (Figs. 1 and 2) did not always show the expected alternating drying and wetting cycles on both soil sides after each switching event. There was a noticeable drying in the portion of the soil that was not irrigated only in the ‘100-PRD treatment’, during 2004, and in 2003 only in the top 40 cm of the soil profile. In treatment ‘50-PRD’ there were no distinct drying and wetting cycles.

agricultural water management 96 (2009) 282–292

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Fig. 1 – Evolution of soil water content at different depths in the PRD irrigation treatments for the 2003 season. Soil water content values are separated for both sides of the vines, north and south, that were alternatively irrigated on a fortnightly basis. Irrigation on each side of the vine started on the day indicated in the legend.

The minimum cPD values measured in the non-irrigated vines were lower in 2003 (0.6 MPa) than in 2004 (0.4 MPa) (Fig. 3). As expected non-irrigated vines tended to have lower early morning and midday leaf and stem water potentials than any of the other treatments. However, differences among treatments were larger and more distinct in determinations performed at pre-dawn or early in the morning than at midday. Differences in plant water status between PRD and conventional drip irrigation were not clear for any given amount of irrigation applied (Fig. 3). Stomatal conductance of the rainfed vines was consistently lower than that of the irrigated vines (Fig. 4). In agreement with the cpd seasonal differences (Fig. 3) stomata of the rainfed vines were in general more closed in 2003 than in 2004. Stomatal conductance was mainly affected by the

irrigation dose and no differences could be observed between PRD and conventional drip irrigation. Also in the diurnal cycle of August 13, 2004 (Fig. 5) it was observed that before dawn, as well as during the first hour of the morning and the last hour of the evening, the non-irrigated vines had lower cs values than the irrigated ones, but at midday the differences are minimal and not significant (P > 0.05). As for gs, it is lower along the whole day in the non-irrigated than in the irrigated vines (Fig. 5). However, the differences were more evident at the first morning hour than at midday, when with a vapor pressure deficit of 4.0 kPa, stomatal closure was observed in all treatments. During the whole course of the day, PRD and conventional drip irrigation did not show differences in cs nor in gs. Pooling data from both seasons, but separated according to md and the type of irrigation, similar gs values for a given cem s , cs

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agricultural water management 96 (2009) 282–292

Fig. 2 – Evolution of soil water content at different depths in the PRD irrigation treatments for the 2004 season. Soil water content values are separated for both sides of the vines, north and south, that were alternatively irrigated on a fortnightly basis. Irrigation on each side of the vine started on the day indicated in the legend.

cmd could be observed in both PRD and conventional drip l irrigation (Fig. 6). For the relationship between gs and cpd there was a trend to lower stomatal conductance for a given cpd in the PRD treatments but differences in slopes nor interception between the linear regressions were not significant (P > 0.05).

3.2.

Vegetative growth, yield and crop load

There were large differences in vegetative growth between years (Table 2). In both seasons, irrigation significantly increased leaf area only in the more irrigated treatments.

Table 2 – Leaf area and pruning weight of the different treatments during each season Parameter

Year 2

1

NI

50

50-PRD

Leaf area (m vine )

2003 2004

4.8 8.4

5.6 9.4

5.6 9.5

Pruning weight (kg vine1)

2003 2004

0.85 1.54

1.18 * 1.73 *

0.99 1.74 *

100 *

6.2 10.4 * 1.25 * 1.92 *

100-PRD *

6.6 10.9 * 1.16 * 2.01 *

PRD at 50

PRD at 100

PRD

n.s. n.s.

n.s n.s

n.s. n.s.

n.s. n.s.

n.s n.s

n.s. n.s.

The asterisk indicates significant differences among irrigation treatments and the control (non-irrigated, NI) based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. n.s.: non-significant.

agricultural water management 96 (2009) 282–292

287

Fig. 3 – Seasonal variation of: (A) pre-dawn water potential (cpd), (B) early morning stem water potential ðcem s Þ, (C) midday md Þ and (D) midday leaf water potential ðc Þ. Values are treatment means W standard error of 8 stem water potential ðcmd s l leaves determinations. DOY, day of the year, CV coefficient of variation. In A rainfall is shown as bars originating from the x axis.

Fig. 4 – Seasonal variation of midday stomatal conductance (gs). Values are treatment means W standard error of 12 leaves per treatment. DOY, day of the year.

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Fig. 5 – Diurnal cycle of (A) stem water potential (cs) and (B) stomatal conductance (gs) carried out on 13th August 2004. Values are treatment means and standard errror of 8 and 12 determinations for water potentials and stomatal conductance, respectively.

Compared with non-irrigated vines pruning weights were significantly higher in all treatments except the ‘‘50-PRD’’ treatment in 2003, and in all treatments in 2004 (Table 2). In both seasons vegetative growth was not affected by PRD.

Seasonal berry growth was mainly affected by the irrigation amount but, within each irrigation dose, similar values of berry fresh weight were observed in PRD and conventional irrigation for both seasons (Fig. 7).

Fig. 6 – Relationship of midday stomatal conductance (gs) with: (A) pre-dawn leaf water potential (cpd), (B) early morning md md stem water potential ðcem s Þ, (C) midday stem water potential ðcs Þ and (D) midday leaf water potential ðcl Þ. Values are separated according to the type of irrigation. There were no significant (P < 0.05) differences in slopes between PRD and conventional drip irrigation, hence unique regression lines, pooling data across treatments, is presented. Values are means of 8 and 12 leaves for c and gs determinations, respectively. r2 values with indication of significance at 1% (***) and at 5% (**) are also shown.

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agricultural water management 96 (2009) 282–292

Fig. 7 – Seasonal variation of berry fresh weight in 2003 and 2004. Values are treatment means W standard error of 6 samples per treatment.

In 2003 there were no significant differences among treatments in yield, which were relatively low in general, in the 6.0–6.5 t ha1 range. In the following year crop levels were in general much larger as number of cluster was about double than in the previous year. All irrigated treatments had

significantly higher yield than the rainfed one, mainly due to the increased berry and cluster weight with irrigation amount. However, there were no significant differences between PRD and conventional drip irrigation in yield and yield components.

Table 3 – Yield and yield components of the different treatments during each season Parameter

Year

NI

50

50-PRD

100

100-PRD

PRD at 50

PRD at 100

Yield (t ha )

2003 2004

6.3 14.2

6.5 17.0 *

6.5 16.7 *

6.0 18.3 *

6.5 18.7 *

n.s. n.s.

n.s. n.s.

n.s. n.s.

Clusters per vine

2003 2004

11 21

11 21

11 21

10 21

11 22 *

n.s. n.s.

n.s. n.s.

n.s. n.s.

Cluster weight (g)

2003 2004

333 407

342 476 *

343 480 *

346 504 *

360 513 *

n.s. n.s.

n.s. n.s.

n.s. n.s.

Berries per cluster

2003 2004

149 192

142 195

148 199

135 198

143 198

n.s. n.s.

n.s. n.s.

n.s. n.s.

Berry weight (g)

2003 2004

n.s. n.s.

n.s. n.s.

n.s. n.s.

1

2.2 2.1

2.3 2.4 *

2.5 * 2.5 *

2.2 2.3 *

2.4 2.5 *

PRD

The asterisk indicates significant differences among irrigation treatments and the control (non-irrigated, NI) based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. n.s.: non-significant.

Table 4 – Leaf area to yield and yield to pruning weight ratio of the different treatments during each season Parameter

Year

NI

50

50-PRD

100

100-PRD

PRD at 50

PRD at 100

Leaf area/yield (m kg )

2003 2004

2.0 1.0

1.4 0.8

1.7 0.9

1.8 0.9

2.5 0.9

n.s. n.s.

n.s. n.s.

n.s. n.s.

Yield/pruning weight (kg kg1)

2003 2004

4.2 5.7

4.0 6.9 *

4.3 6.6

3.0 6.4

3.6 6.3

n.s. n.s.

n.s. n.s.

n.s. n.s.

2

1

PRD

The asterisk indicates differences among irrigation treatments and the control (non-irrigated, NI) based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. n.s.: non-significant.

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Table 5 – Parameters of must quality of the different treatments during each season Parameter

Year

NI

*

100

22.3 20.8 * 23.1 *

22.0 21.4 * 24.9 *

2003 2004-eh 2004-lh

pH

2003 2004-eh 2004-lh

3.33 3.16 3.21

3.50 * 3.21 3.27

3.49 * 3.24 * 3.31 *

3.44 3.28 * 3.39 *

2003 2004-eh 2004-lh

4.7 5.7 5.4

4.3 5.9 5.9

4.2 6.0 5.5

2003 2004-eh 2004-lh

1.0 1.4 1.4

1.1 1.9 * 1.9 *

2003 2004-eh 2004-lh

4.7 5.5 6.3

4.5 5.5 5.9 *

Malic acid (g L1)

Tartaric acid (g L1)

22.5 20.8 * 22.8 *

50-PRD

Total soluble solids (Brix)

Titratable acidity (g L1 tartaric acid)

21.6 19.7 21.3

50

100-PRD PRD at 50 PRD at 100 21.9 20.9 * 23.6 *

PRD

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

3.40 3.23 * 3.33 *

n.s. n.s. n.s.

n.s. n.s.

n.s. n.s. n.s.

4.5 6.3 5.6

4.2 6.3 5.3

n.s. n.s. n.s.

1.3 * 1.9 * 1.6

1.4 * 1.8 * 1.8 *

1.2 1.6 1.5

4.5 5.2 6.0

4.5 5.4 6.4

4.3 5.2 5.9 *

* *

n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s.

n.s. n.s.

*

*

n.s. n.s. n.s.

n.s. n.s.

n.s. n.s. n.s.

*

For year 2004 values from the early (2004-eh) and late harvest (2004-lh) are separately analyzed. The asterisk indicates significant differences among irrigation treatments and the control (non-irrigated, NI) based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. *Significant at P < 0.05; n.s., non-significant.

Crop load, either expressed as leaf area to yield or as yield to pruning weight, was not significantly affected by the irrigation type nor by the irrigation dose (Tables 3 and 4).

3.3.

in wines. Similarly, pH significantly increased in both treatments irrigated at 50% of ETc in the must, but again not in the wines. In 2003 there were no significant differences between PRD and conventional drip irrigation in any of the must and wine quality parameters analyzed. In both harvests of 2004 irrigation had large effects on must and wine composition. Irrigation increased must total soluble solids concentration and wine alcohol content. Again, there were no significant differences between PRD and conventional drip irrigation on these parameters. Irrigation increased pH and malic acid in must and wine. Significant differences on must and wine pH attributable to

Must and wine composition

In 2003 the irrigation regime did not have any considerable effect on must and wine composition (Tables 5–7). Wine alcohol content, anthocyanins concentration, wine color and total phenolic were not significantly affected by the irrigation applied (Table 7). The only significant changes due to irrigation were an increase in malic acid concentration in musts but not

Table 6 – Parameters of wine quality, before malolactic fermentation, of the different treatments during each season Parameter

Year

NI

50

Ethanol (8 Vol)

2003 2004-eh 2004-lh

12.3 11.2 12.8

12.9 12.1 * 13.7

Wine pH

2003 2004-eh 2004-lh

3.76 3.26 3.19

3.87 3.35 3.34 *

3.94 3.48 * 3.42 *

3.94 3.47 3.49 *

2003

5.0

4.9

4.3

2004-eh 2004-lh

6.8 7.1

6.8 7.0

Malic acid (g L1)

2003 2004-eh 2004-lh

1.4 2.0 1.3

Tartaric acid (g L1)

2003 2004-eh 2004-lh

3.2 3.8 * 2.4

Titratable acidity (g L1 tartaric acid)

50-PRD

PRD at 50

PRD at 100

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

3.86 3.43 3.39 *

n.s.

n.s. n.s. n.s.

n.s.

4.8

5.4

n.s.

n.s.

*

6.6 7.0

6.8 6.7

6.6 6.6

n.s. n.s.

n.s. n.s.

n.s. n.s.

1.8 2.3 1.6

2.0 2.4 1.6

1.6 2.6 1.9

2.4 2.3 1.7

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

2.8 * 3.3 * 2.2

2.7 * 2.9 * 2.0

2.7 * 2.7 * 1.9

2.7 * 2.9 2.2

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

12.8 11.9 13.4

100 12.6 12.2 * 14.6

100-PRD 12.6 12.0 14.2

* *

PRD

*

n.s.

For year 2004 values from the early (2004-eh) and late harvest (2004-lh) are separately analyzed. The asterisk indicates significant differences among irrigation treatments and the control (non-irrigated, NI) were based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. *Significant at P < 0.05; n.s., non-significant.

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Table 7 – Parameters of wine quality, before malolactic fermentation, of the different treatments during each season Parameter

Year

NI

50

2003 2004-eh 2004-lh

486 448 482

484 443 441

440 502 545

408 488 570

Total phenolics index (AU)

2003 2004-eh 2004-lh

50 49 54

52 49 53

47 51 50

45 50 55

Color intensity (AU)

2003 2004-eh 2004-lh

1

Anthocyanins (mg L )

8.8 8.9 9.9

8.2 9.0 8.2

50-PRD

7.3 8.4 8.8

100

8.1 8.0 9.3

100-PRD

PRD at 50

PRD at 100

447 472 571

n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s

48 50 54

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

6.1 8.1 9.7

*

PRD

For year 2004 values from the early (2004-eh) and late harvest (2004-lh) are separately analyzed. The asterisk indicates significant differences among irrigation treatments and the control (non-irrigated, NI) based on Dunnett’s t test at P < 0.05. The significance of the contrast between PRD and conventional drip irrigation are also indicated. *Significant at P < 0.05; n.s., non-significant.

PRD, were also observed, but differences were not consistent between the two irrigation levels, PRD increasing must and wine pH at the low irrigation amount, but decreasing pH when applied at 100% of ETc. Wine phenolics content was not significantly impaired by irrigation in none of the two 2004 harvests. The only significant effect of PRD was an increase in anthocyanins in the 50-level but not in the 100. This effect could be observed in both harvests but it was statistically significant only in the latter.

4.

Discussion

Water relations and vine growth were not affected by the PRD type of irrigation. Probably because of this, vine performance and fruit and wine composition were not different in the PRD than in the conventional drip-irrigation treatments. Indeed, applying irrigation alternatively to only one side of the vine did not have any beneficial, nor negative effect, on the overall vineyard performance, when compared to similar amount of irrigation applied conventionally. However, it should be noted that, at a grower scale, to properly manage a PRD type of irrigation, it is necessary to double the pipe lines and the control valves. This leads to a more expensive irrigation system for growers. The lack of any considerable effect of PRD might have been due to the frequent absence of clear soil drying and wetting cycles between the two sides of the vine. However, even in treatment ‘100-PRD’ that did show, particularly in 2004, the expected drying and wetting patterns, the agronomic and fruit quality response were not different than in the ‘100’ treatment. In view of the soil water content data here reported one may speculate that a different switching pattern should have been applied. Longer drying cycles, to dry a higher proportion of fine and active roots could be applied in order to exploit more efficiently root-to-shoot signalling. The proper length of the drying period will however be difficult to determine by growers, who often cannot afford the expensive soil water measurement equipment required to properly monitoring soil water status. In potted plants it is easy to separate the rootzone in dry and wetted areas. Under these conditions PRD has been shown to have the potential to increase water use efficiency (Antolı´n et al., 2006). In the field, instead, there are not only some

examples of successful PRD (Dry et al., 2001; de Souza et al., 2003; dos Santos et al., 2003; Du et al., 2008), but also other cases where PRD did not have any considerable effect on grape performance (Bravdo et al., 2004; Gu et al., 2004; Pudney and McCarthy, 2004). This difference might be because of different soil and environmental conditions, as well as the system of irrigation employed. In this sense conventional drip irrigation, as applied in our study, can be also considered already as a type of partial rootzone drying, but without any alternation in water application as in the PRD irrigation system. It seems then that for heavy textured and deep soils, under drip irrigation, as in our study, it is difficult to achieve a proper separation between wet and dry portions of the rizosphere questioning the transferability of the PRD technique to these conditions. This is even more complex in environments such as the Mediterranean one, where rain is scarce, but still there is some erratic precipitation during the summer. Under these conditions growers should carefully consider the convenience of using this type of irrigation in their vineyard. Similarly to our results Marsal et al. (2008), also working with Tempranillo grapes, showed that the expected physiological PRD mechanisms could not be achieved. Despite that, they still reported some indirect beneficial effect brought by PRD due to the smaller soil portion wetted by PRD and hence a higher efficiency in water application was obtained. This was not the case, however in our experiment. In our conditions it seems therefore more important to focus research on the effects of the irrigation dose and timing of application on vine performance and fruit quality. In this sense it should be noted that the clearest effect of irrigation on must and wine composition was the increase in wine pH. This is because irrigation altered the balance between malic and tartaric acid, with a tendency to increase the first and to decrease the latter. Given that malic is a weaker acid than tartaric, the overall effect of irrigation on wine pH was to increase it. An increase in wine pH might be detrimental to sanitary and aging stability of the wines made from the irrigated vines and it has been also previously reported in other irrigation trials (Freeman and Kliewer, 1983). From our results it is also clear that more effort should be conducted to explore the possible interaction between irrigation and crop level. In fact, due to the different numbers of shoots retained after shoot pruning, and therefore different

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agricultural water management 96 (2009) 282–292

numbers of cluster per vine collected (Table 3), there were larger differences in yield between both seasons. In 2003, yield was very low, and irrigation did not improve vineyard productivity probably because yield was more constrained by the few shoots retained after pruning rather than by vine water status or the environmental conditions. In 2004, with a general high crop level, the supplemental irrigation improved vine yield, as well as it increased sugar and alcohol level of wines without any detrimental effect on wine phenolic contents. This suggests that the vine response to irrigation might well be different according to its crop level as in occasions reported for other grape cultivars (Bravdo et al., 1984; Poni et al., 1994).

Acknowledgements This research was supported by funds from the Generalitat Valenciana, Consellerı´a de Agricultura, Pesca y Alimentacio´n, Project No. 2002TAHVAL0034. We are grateful to the STR personnel for the meteorological data, to Dr. E. Carbonell for statistical analysis of data and to personnel from Caja Campo for the field determinations. Thanks are also due to the ‘‘Estacio´n de Viticultura y Enologı´a, Requena’’ for the vinifications and to the Fundacio´n Lucio Gil de Fagoaga for allowing this research activity in its vineyard.

references

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