Effects of climate variability on irrigation scheduling in white varieties of Vitis vinifera (L.) of NW Spain

Agricultural Water Management 170 (2016) 99–109

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Effects of climate variability on irrigation scheduling in white varieties of Vitis vinifera (L.) of NW Spain Javier José Cancela a,∗ , Emiliano Trigo-Córdoba a,b , Emma María Martínez a , ˜ a , José Manuel Mirás-Avalos b Benjamín Jesús Rey a , Yolanda Bouzas-Cid b , María Fandino a GI-1716, Proyectos y Planificación, Dpto. Ingeniería Agroforestal, Universidad de Santiago de Compostela, Escuela Politécnica Superior, Campus Universitario s/n, 27002 Lugo, Spain b Estación de Viticultura e Enoloxía de Galicia (EVEGA-INGACAL), Ponte San Clodio s/n, 32428, Leiro, Ourense, Spain

a r t i c l e

i n f o

Article history: Received 27 August 2015 Received in revised form 1 January 2016 Accepted 7 January 2016 Available online 25 January 2016 Keywords: ˜ Albarino Bioclimatic indices Godello Soil water content Stem water potential Water productivity

a b s t r a c t Inter-annual climate variability, mainly rainfall temporal distribution, is a critical factor for scheduling irrigation. In order to efficiently manage precision irrigation systems for Vitis vinifera (L.), their effects on plant physiology, and vineyard soils, together with yield and quality parameters, need to be understood. ˜ and The current study was conducted on two grapevine cultivars from Galicia (NW-Spain), cv. ‘Albarino’ ‘Godello’, during 2012–2014, in two different Designations of Origin (DO): Rías Baixas and Valdeorras. The treatments were rainfed (R) and surface drip irrigation (DI) in DO Rías Baixas, adding subsurface drip irrigation (SDI) in DO Valdeorras, with four replicates (7 plants each). Irrigation was triggered at fruit set, when midday stem water potential (stem ) dropped to −0.5 MPa, and stopped 15 days before harvest in DO Valdeorras; but it was managed by the vinegrower in DO Rías Baixas. Different bioclimatic indices were calculated to characterize each season and location. Soil water content and stem were periodically measured to assess vineyard water status. Yield and juice quality attributes were determined. Water productivity indices were calculated to compare locations and cultivars. Differences between DOs were observed regarding bioclimatic indices, which indicated temperate and very cool nights for cv. ‘Godello’. In ˜ warmer nights were observed. In DO Valdeorras, the differences between treatments the case of ‘Albarino’, in stem were never higher than −0.19 MPa; whereas they were almost null in DO Rías Baixas. Yield parameters showed a worse overall productive performance for the R treatment, with lower yields in 2012 and 2013. Qualitative parameters were stable over the three growing seasons studied. Adjusting irrigation schedules for a given season using stem measurements and considering the phenological stage of the vine might help to obtain homogeneous harvests, both in yield and quality. Water productivity indices related with grape yield and pruning weight showed that, in a temperate climate, vegetative growth has an important weight in vineyard water use. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Although grapevine (Vitis vinifera L.) is a species with a great drought-tolerance, its potential water needs (i.e., vineyard ETc under no stress limitations) are relatively high (Williams and Ayars, 2005), as is the case for Galician grapevine cultivars such ˜ and ‘Godello’. as ‘Albarino’ It is well-known that both water deficit and surplus affect grape composition and quality and, therefore, adequate soil water availability, according to the phenological stage of the vines, must be

∗ Corresponding author. E-mail address: [email protected] (J.J. Cancela). http://dx.doi.org/10.1016/j.agwat.2016.01.004 0378-3774/© 2016 Elsevier B.V. All rights reserved.

maintained over the growing season in order to obtain good-quality grapes (Jackson and Lombard, 1993; Deloire et al., 2004). Hence, vineyard irrigation strategies must be adapted to both the cultivar and the region where it is grown. In this regard, deficit irrigation strategies have been successfully adopted as management tools in vineyards to ensure an adequate balance between vegetative and reproductive development while preserving yield and water resources and improving fruit composition (Dry et al., 2001; Intrigliolo and Castel, 2008; dos Santos et al., 2003). Furthermore, the predictions about global warming suggest a reduction in rainfall and an increased evapotranspiration in Southern Europe for the near future (IPCC, 2007). This may cause that grapevine cultivars adapted to temperate and cool climates to reach their temperature maximum threshold and, consequently,

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lose their specific organoleptic qualities (Horacio García and DíazFierros, 2009). Vinegrowers concern about the negative impacts of water deficits on vine growth, yield and to secure and stabilize production (Gouveia et al., 2012) has increased the use of irrigation in vineyards, even in Galicia (NW Spain), which is considered a region that receives high amounts of rainfall (from 700 mm to 1900 mm, depending on the site within the region); however, irri˜ et al., gation studies in vineyards of this region are scarce (Fandino 2012; Cancela et al., 2015; Trigo-Córdoba et al., 2015). Moreover, due to global water scarcity, agricultural water use is in competition with the rest of water users (industry, ecological, human) (Cosgrove and Rijsberman, 2000). For this reason it is necessary to base agricultural water use according to sustainability criteria, assessing its impact on production and economic terms. Pereira et al. (2012) reported a discussion about water use indicators, namely water use efficiency (WUE) and water productivity (WP), that have been indistinctly used by several authors. This aspect has led to difficulties in comparing the results from different research efforts; therefore it is critical to define exactly the terms used in the calculation of these indices. Teixeira et al. (2007) used different crop water productivity indices, taking into account crop transpiration, evapotranspiration and irrigation water use; however Flexas et al. (2010) used WUE as a plant physiology term that represents the performance of a given plant or variety in using water. Recently, Medrano et al. (2015) applied both focuses, without exactly reflecting the term WP, in this case no relationships between total water applied and yield were shown, including irrigation treatments. In this context, field trials dealing with timing and amount of water applied through irrigation in accordance with the characteristics of the different cultivars and regions are needed (dos Santos et al., 2007; Intrigliolo et al., 2012; van Leeuwen et al., 2009), even under cool-humid climates (Reynolds et al., 2007). Therefore, the objectives of the current study were to: (a) provide tools for irrigation control and management in two different climatic conditions in an Atlantic region; (b) study the effects of irrigation on the production and musts composition in two Galician ˜ cultivars (‘Godello’ and ‘Albarino’) during the period 2012–2014; (c) evaluate the water productivity in agronomic terms, considering grape yield and pruning weight, to allow for comparison between different wine regions in the world. 2. Materials and methods 2.1. Site description In this work, two field sites were studied. They were located within two different wine Designations of Origin (DO) in Galicia: Rías Baixas and Valdeorras (Fig. 1). 2.2. DO Rías Baixas The experiment was carried out, from 2012 to 2014, in an ˜ vineyard planted in 1996 on 110-Richter at a spacing ‘Albarino’ of 3 × 2 m (1667 vines ha−1 ). The vineyard was located in O Rosal (Pontevedra, NW Spain) within the Rías Baixas DO (41◦ 57 6 N, 8◦ 49 26 W, elevation 101 m). Vines were trained to a vertical trellis system on a Guyot oriented in the East–West direction. The soil at this site presented a sandy-loam texture (66.1% sand, 18.5% silt and 15.4% clay), slightly acid [pH (H2 O) 6.2] and with a high organic matter content (7.8%). Soil depth varied with the slope of the plot, in average it was deeper than 1.2 m; available water capacity (AWC) was about 156 mm m−1 . AWC was calculated as the difference between the average higher values of field capacity (FC) and average lower values of permanent wilting point (PWP),

measured with the TDR100 (Campbell Scientific) at 1.00 m depth, during the three study years.

2.3. DO Valdeorras The study was conducted in a commercial ‘Godello’ vineyard during three consecutive seasons (2012–2014) planted in 1997 on 110-Richter at a spacing of 1.35 × 1.95 m (3800 vines ha−1 ). This vineyard was located in A Rúa (Ourense, NW Spain) within the Valdeorras DO (42◦ 23 59 N, 7◦ 7 15 W, elevation 320 m, mean slope is 18%). Vines were trained to a vertical trellis on a double cordon system oriented in the North–South direction. The soil at this site presented a loamy texture (46.2% sand, 31% silt and 22.8% clay), very acid [pH (H2 O) 4.99] and with a medium organic matter content (2.26%). Soil depth was, approximately, 1.2 m and total AWC was about 170 mm m−1 ; this value was calculated using the same methodology applied to DO Rías Baixas.

2.4. Experimental design and irrigation treatments In DO Rías Baixas, two treatments were established following a completely randomized-block design with four replications (7 control plants each). The treatments were: rainfed (R) and surface drip irrigation (DI). Each replicate consisted of three rows with 14 vines per row. The seven vines in the centre of the middle row were used for measurements and the rest acted as buffers. The DI pipes were in the vineyard row at 40 cm above the soil, with two emitters of 4 L h−1 per vine. The irrigation management was established by the vinegrower, applying water from Monday to Friday, from 26th July to 8th August in 2012, during August in 2013 and from mid-July to late August in 2014. Daily irrigation depth was 5.3 mm, usually applied during 4 h per day (2 h rarely), during the morning. The total irrigation depth per season was 16, 32 and 66 mm, in 2012, 2013 and 2014, respectively. During these seasons, the number of irrigation events was 3, 6 and 13 in 2012, 2013 and 2014, respectively. In DO Valdeorras, three treatments were established following a completely randomized-block design with four replications (7 control plants each). Each replicate consisted of three rows with 14 vines per row. The seven vines in the centre of the middle row were used for measurements and the rest acted as buffers. The treatments were: rainfed (R), surface (DI) and subsurface (SDI) drip irrigation. The DI pipes were in the vineyard row at 40 cm above the soil; whereas those for SDI were 40 cm deep into the soil, where the main active roots are disposed. Both systems were equipped with 2 L h−1 emitters (Cancela et al., 2015), one emitter per vine in the case of DI, whereas SDI have one emitter per meter. The irrigation treatment began at fruit set, early June (stem water potential value of −0.5 MPa), and finished at ripeness (mid to late August), approximately two weeks prior to harvest (2012-Sep, 7; 2013-Sep, 16 and 2014-Sep, 3). During this period, water was daily applied early in the morning, with an average total dose per season of 80, 63 and 46 mm, in 2012, 2013 and 2014, respectively. Irrigation treatments began the first of June and finished in the middle of August in 2012; during 2013, irrigation started on July and finished at the end of August; however in 2014, due to problems with the pumping system, irrigation started in the middle of July and finished at the end of August. During these seasons, water was applied for 59, 46 and 34 days in 2012, 2013 and 2014, respectively, at a rate of 1.5 h per day, in order to reduce evaporation losses. Average daily irrigation depths were 1.14 mm and 1.54 mm, for DI and SDI, respectively.

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Fig. 1. Location of the experimental sites (

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) within the Galician viticultural Designations of Origin (NW Spain—Iberian Peninsula).

2.5. Climate data, field measurements and laboratory determinations Data on air maximum and minimum temperatures, rainfall, relative humidity, wind speed and solar radiation were collected at weather stations managed by MeteoGalicia, the Galician Mete˜ orological Agency, ‘As Eiras’ (DO Rías Baixas, cv. ‘Albarino’) and ‘Larouco’ (DO Valdeorras, cv. ‘Godello’) located in the vicinity of the experimental vineyards, less than 7 km. Reference evapotranspiration (ETo ) was calculated using the FAO Penman–Monteith equation for limited weather data, i.e., estimating the actual vapor pressure from the daily minimum temperature and solar radiation from daily maximum and minimum temperatures (Allen et al., 1998). In addition, from the weather data, several bioclimatic indices were computed according to Tonietto and Carbonneau (2004), including dryness index (DrI), heliothermal index (HI) and cool-night index (CI). Soil water content (SWC) was measured every two weeks with a TDR100 (Campbell Scientific) equipment, using the PCTDR software with a flexible connector (Souto et al., 2008). Observations were performed at 60 cm depth. The equation of Topp et al. (1980) relating the volumetric water content () with the measured bulk dielectric constant (εeff ) was used, since it has been proven successful in soils that do not contain substantial amounts of bound water, e.g., most sandy and loamy soils (Robinson et al., 2003), as those from the studied plots. Eight measurements per treatment were carried out. The measurement points were placed in the vine row, at 0.60 m from the emitters and 0.30 m apart from the vine trunk, allowing tillage operations. Midday stem water potential (stem ) was assessed fortnightly on one mature and healthy leaf of three plants per replicate (thus, twelve plants per treatment), using two pressure chambers (PMS Model 600, Albany, OR, USA and Soil Moisture Inc., Santa Barbara, CA, USA). Leaves were covered with a plastic bag and aluminium foil for at least 1 h prior to the measurements (Choné et al., 2001).

This modality of leaf water potential has been proven more useful than predawn leaf water potential for estimating the vine water status of Galician grapevine cultivars (Mirás-Avalos et al., 2014). Yield was determined at harvest on 7 vines per replicate. The number of clusters per vine was also recorded. Average cluster weight was computed by dividing yield per plant by the number of clusters. Pruning weight (PW) was determined at winter in five vines per replicate, during pruning 30 and 12 buds were retained ˜ and. ‘Godello‘, respectively. The Ravaz Index (ratio in cv. ‘Albarino‘ between yield and PW) was also calculated. Grape lots of approximately 40 kg per treatment were manually harvested. These grapes were destemmed, crushed and the must obtained. Basic parameters of musts (probable alcoholic grade, pH, titratable acidity, tartaric and malic acid contents) were determined by Fourier transform infrared spectrometry (FTIR) using a WineScan FT120 analyzer (FOSS Electric, Barcelona, Spain) calibrated according to the official methods (OIV, 2009).

2.6. Water productivity WP may express a physical ratio between yields and water use, or between the value of the product and water use (Rodrigues and Pereira, 2009). Therefore, it is very important to define exactly the concepts used in the equation (numerator and denominator) for determining WP. In our study, WP is defined as the ratio between vineyard grape yield and the total water use (TWU), in kg m−3 (WPGrape ). WPGrape =

Y TWU

(1)

where Y, is the yield per hectare in kg (Section 2.5); and TWU corresponds to the water used, in m3 ha−1 to achieve Y, i.e., rainfall and irrigation water over the growing season, according to the different treatments considered.

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Since grapevines have an important use of water related with vegetative growth, two new indices were defined for including the pruning wood (Eq. (2)) and grape yield and pruning weight (Eq. (3)). WPPW =

PW TWU

WPGrape+PW =

(2) Y + PW TWU

this water status indicator was observed in 2012, around day 190. In contrast, stem in DO Valdeorras reached values lower than −1.0 MPa in 2012 and 2013, by the end of the season (Fig. 4b). Significant differences among treatments were detected on stem , those values corresponding to the R treatment being more negative than those from DI and SDI. These differences were smaller in 2014 (Fig. 4b).

(3)

where PW refers to pruning wood, expressed in kg per hectare, and Y + PW is the sum of grape yield and pruning wood, also in kg per hectare. 2.7. Statistical analysis A multivariate analysis of variance was performed for all the yield and must quality attributes considered in this study, as well as for WP indices. Tukey’s Honest Significant Difference Test was used for mean separation in the case of the experiment carried out in DO Valdeorras. The statistical software used was SPSS v. 20.0 (IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). 3. Results 3.1. Climate and bioclimatic indices The dynamics of reference evapotranspiration (ETo ) and rainfall distribution over the growing seasons 2012–2014 for the two sites showed different patterns (Fig. 2). In DO Rías Baixas rainfall was higher than in DO Valdeorras over the three seasons, despite the rainfall temporal distribution along the season being similar (same number of rainfall days and on the same dates but with different amounts depending on the site). Total rainfall, from March to harvest, was 593, 791 and 830 mm in DO Rías Baixas; and 260, 331 and 239 mm in DO Valdeorras, for 2012, 2013 and 2014, respectively. Average ETo , from March to harvest, was 715 mm in DO Valdeorras (2012—706 mm, 2013—741 mm, 2014—697 mm), while in DO Rías Baixas was 670 mm (2012—655 mm, 2013—700 mm, 2014—647 mm). Bioclimatic indices showed a temperate climate (HI) for both sites, according to Tonietto and Carbonneau (2004), with the exception of 2014 in DO Valdeorras, where a higher HI (temperate warm) was observed (Table 1). In DO Rías Baixas the nights were classified as temperate (CI > 14 ◦ C) and DrI was framed in humid conditions; however, DO Valdeorras showed lower CI (<14 ◦ C), therefore cool nights; with an average DrI of 18 mm, equivalent to a moderately dry climate type (Tonietto and Carbonneau, 2004). 3.2. Soil and plant water measurements Soil water content at 60 cm showed a similar behavior over the growing season for the different treatments (Fig. 3). In DO Rías Baixas, significantly higher SWC values were detected under the DI treatment around day 225 for 2012 and 2013; whereas in 2014, the year with the greatest SWC values, DI treatment presented significantly higher values than R on the last three measurement dates (Fig. 3a). In DO Valdeorras, a decreasing trend in SWC was observed over the growing season; however, no significant differences among treatments were detected, even though higher SWC were measured under SDI, then under DI and, finally, under R (Fig. 3b). Midday stem values were very similar between treatments in DO Rías Baixas (Fig. 4a). Over the three growing seasons studied, midday stem values more negative than −0.6 MPa were not observed. The only significant difference between treatments for

3.3. Yield and must quality When all the seasons were considered together, treatment only exerted a significant effect on the Ravaz Index for DO Valdeorras (Table 2). The rest of the yield and vegetative growth parameters accounted for in this study were unaffected by the irrigation treatment. In contrast, year significantly influenced cluster weight and pruning weight in both DO and yield in DO Rías Baixas (Table 2). No significant interactions between treatment and year were observed for any of the yield and vegetative growth attributes considered in this study. Similarly, must quality attributes were not significantly affected by irrigation treatment when all years were considered together (Table 2). On the contrary, year exerted a significant influence on probable alcoholic grade and tartaric and malic acid concentrations in the DO Rías Baixas; and only on the tartaric acid concentration in DO Valdeorras (Table 2). No significant interactions between treatment and year were detected for the must quality attributes. When each year was considered separately, no significant differences between treatments were observed for yield components and pruning weight in DO Rías Baixas (Table 3). In the case of DO Valdeorras in 2013, number of clusters per vine was significantly higher for SDI than for R and DI. The rest of the attributes considered did not present any significant difference among treatments (Table 3), except for Ravaz Index in 2012 for both sites, and in 2013 in DO Valdeorras, in these cases the SDI treatment showed the highest values. Similarly, must parameters did not show significant differences between treatments in DO Rías Baixas, except for total acidity in 2013, which was higher for DI musts and pH which was higher for R musts (Table 4). In the case of DO Valdeorras, no significant differences were detected between treatments for any of the must attributes considered; however, a trend to obtain higher probable alcoholic grades and lower acidities under the R treatment was observed (Table 4). 3.4. Vineyard water productivity The WP indices did not show significant differences between treatments in DO Rías Baixas (Table 5), except for WPGrape + PW in 2014, when the R treatment achieved the higher values. On the contrary, a trend to obtain higher WP indices for WPGrape and WPGrape + PW under the irrigation treatment was observed for 2012 and 2013. In contrast, WPPW was higher in the rainfed treatment, for all years. Moreover, year exerted a significant influence in WPGrape and WPPW , mainly due to the results obtained in 2013. For DO Valdeorras, significant differences were detected for WPGrape in 2014, where the R treatment presented the highest value respect to the SDI treatment, whereas the DI treatment showed an intermediate value (Table 5). This trend was also observed in 2012; however WPGrape was higher in the SDI treatment for 2013 when compared with the DI and R treatments. The WPPW index did not show significant differences between treatments, but in general the R treatment showed a higher value than irrigation treatments, except in 2014. Moreover, WPGrape + PW showed the highest values for R, during 2012, without significant differences between treatments (Table 5); the same trend was obtained in 2014. However during 2013, the DI treatment showed the highest value for

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210

240

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90

120

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210

240

9 8

20

7

30

6

40

5

50

4

60

3

70 80

2

90

1

2012

0

0

9

10

8

20

7

30

6

40

5

50

4

60 70

3

80

2

90

1

100

0

0

9

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8

20

ET o (mm d-1)

Precipitation (mm)

300

10

100

Precipitation (mm)

270

-1

150

ET o (mm d )

12 0

2013

7

30

6

40

5

50

4

60

3

70 80

2

90

1

100

0

DO Rías Baixas

-1

90

0

ET o (mm d )

Precipitation (mm)

60

103

2014

DO Valdeorras

Fig. 2. Total rainfall (bars) and daily reference evapotranspiration (lines) at the experimental sites during the seasons of 2012–2014. Data in the X-axis refer to the day of the year.

WPGrape + PW . Finally, a significant effect of the year was found for WPPW . 4. Discussion In our study, the annual pattern of temperature and rainfall showed differences between both DO during the late season; for this reason, DO Rías Baixas has a lower HI than DO Valdeorras, and a humid DrI classification, instead of a moderately dry (DrI)

as DO Valdeorras. In general, DO Valdeorras showed greater water requirements than DO Rías Baixas, due to a higher ETo and scarcer rainfall (two or three times lower). The HI for DO Valdeorras was greater than the values presented by Fraga et al. (2014), that included this region into the Cool class. However, for the rest of the bioclimatic indices shown by these authors for DO Valdeorras and DO Rías Baixas, the classification was coincident with our results. This slight disagreement might have been caused by the weather stations used in the study of Fraga et al. (2014), which are

Table 1 Bioclimatic indices for DO Rías Baixas and DO Valdeorras during each growing season. Abbreviations: HI = Heliothermal index, DrI = Dryness index, CI = Cool night index. Site—DO

Season

HI ◦

Rías Baixas

Valdeorras

a

DrI

CI

mm

◦

2012

1830.4

304.9

14.3

2013

2059.2

168.1

14.6

2014

1977.3

379.1

15.2

Average

1955.6

284.0

14.7

2012

1969.6

54.6

11.7

2013

2090.9

−8.2

12.7

2014

2124.3

10.0

13.4

Average

2061.6

18.8

12.6

According to Tonietto and Carbonneau (2004).

C

Classificationa

C HI-1, CI-1, DI-2 Temperate, temperate nights, humid HI-1, CI-1, DI-2 Temperate, temperate nights, humid HI-1, CI-1, DI-2 Temperate, temperate nights, humid HI-1, CI-1, DI-2 Temperate, temperate nights, humid HI-1, CI + 2, DI-1 Temperate, very cool nights, sub-humid HI-1, CI + 1, DI + 1 Temperate, cool nights, moderately dry HI + 1, CI + 1, DI + 1 Temperate warm, cool nights, moderately dry HI-1, CI + 1, DI + 1 Temperate, cool nights, moderately dry

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Fig. 3. Seasonal evolution of soil water content for the treatments studied during 2012–2014 growing seasons at a DO Rías Baixas and b DO Valdeorras. Each point represents the average of 8 measurements. Bars indicate the standard error of the mean. Asterisks indicate significant differences among treatments (p < 0.05).

situated at higher altitude than the one used in our work. Climate conditions are very relevant to schedule irrigation management, not only under arid and semi-arid conditions, but also in temperate climates, mainly due to changes in the temporal distribution of precipitation (Cruz et al., 2009), related with climate change. For this

reason, in the temperate climate of NW Spain, several works have ˜ et al., 2012; Trigo-Córdoba et al., 2015) been published (Fandino to understand the effects of the increasing use of irrigation systems on vineyard water requirements and yield. Schultz and Stoll (2010) discussed about the use of several parameters for a dynamic

Table 2 ˜ and ‘Godello’ grapevines for yield and vegetative growth and must quality attributes (p-values are shown). Values in bold indicate significant Analysis of variance for ‘Albarino’ differences at p < 0.05. Site and cultivar Yield and vegetative growth components DO Rías Baixas ˜ ‘Albarino’

DO Valdeorras ‘Godello’

Must quality attributes DO Rías Baixas ˜ ‘Albarino’

DO Valdeorras ‘Godello’

a

Variable

Treatmenta

Yeara

Treatment* Yeara

Yield Clusters Cluster weight Pruning weight Ravaz index Yield Clusters Cluster weight Pruning weight Ravaz index

0.354 0.499 0.274 0.849 0.173 0.336 0.254 0.123 0.110 0.009

0.002 0.099 <0.001 0.030 0.186 0.086 0.936 0.005 0.005 0.017

0.555 0.522 0.353 0.699 0.329 0.215 0.386 0.351 0.932 0.321

Probable alcoholic grade Total acidity pH Tartaric acid Malic acid Probable alcoholic grade Total acidity pH Tartaric acid Malic acid

0.960 0.602 0.287 0.526 0.959 0.650 0.093 0.375 0.053 0.692

<0.001 0.065 0.436 <0.001 0.002 0.168 0.395 0.361 <0.001 0.071

0.964 0.833 0.535 0.773 0.890 0.889 0.857 0.940 0.271 0.767

Data from the three studied years were pooled in order to carry out this analysis.

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105

˜ and b ‘Godello’ cultivars under the treatments studied during 2012–2014 growing seasons. Each Fig. 4. Seasonal evolution of midday stem water potential for a ‘Albarino’ point represents the average of 12 measurements. Bars indicate the standard error of the mean. Asterisks indicate significant differences among treatments (p < 0.05). Arrows indicate the starting and ending date of the irrigation period.

scheduling of irrigation in vineyards, as well as Mirás-Avalos et al. ˜ ‘Treixadura’ and ‘Godello’ with a study of (2014) for cv. ‘Albarino’, diurnal changes in leaf water potential in order to determine the best water status indicator for Galician cultivars; and Cancela et al. (2015) for cv. ‘Godello’ and ‘Mencía’, appling soil and plant water status relationships for irrigation purposes, mainly to start irrigation. In general, all authors referred to the necessity of appling a set of indices, including soil and plant indicators, to achieve an efficient irrigation management in vineyards (Williams and Trout, 2005). Several authors considered stem as a reliable indicator of vine water status (Choné et al., 2001; Cole and Pagay, 2015; MirásAvalos et al., 2014) that may be useful for irrigation scheduling. However, a strong water limitation induces stomatal closure and leaf area reduction (Intrigliolo and Castel, 2006), which can cause that vines under rain-fed and irrigation conditions present the same values for midday stem and leaf water potentials. These conditions did not occurr in the viticultural Galician regions; for this reason, midday stem is the better plant water status indicator. Moreover, it takes into account the overall plant water status, and it is not dependent on the variability of weather conditions, as leaf water potential does. Over the three seasons studied, a progressive decline of stem water potential values was observed in both treatments for both cultivars (Fig. 4). This decrease has been caused by the increasing evaporative demand observed along the growing season, due to higher temperatures and solar radiation values, as well as to soil water content depletion (Fig. 3). Irrigation allowed ‘Godello’ vines to maintain a higher water status than those rain˜ vines did not present significant differences fed, whilst ‘Albarino’ on their water status as a function of irrigation. At the end of August,

rain-fed ‘Godello’ vines reached −1.0 MPa of stem water potential, indicative of a mild water deficit (Deloire et al., 2004; van Leeuwen et al., 2009). ˜ vines in DO Rías Baixas did not reach stem In contrast, ‘Albarino’ water potential values lower than −0.6 MPa independently of the treatment, indicating that they did not experience water restrictions (van Leeuwen et al., 2009). Furthermore, stem water potential values for this cultivar were less negative each passing year, reflecting the progressive irrigation increase that the vinegrower used in this plot, also displayed by higher soil water contents (Fig. 3), and higher precipitation during the second and third seasons. Several authors discussed about the relevance of taking into account both soil and plant based indicators for irrigation management (Williams and Trout, 2005; Centeno et al., 2010). Cancela et al. (2015) recommended triggering the irrigation when a threshold value of soil water potential (−0.10 MPa), related with stem water potential for ‘Godello’ (stem = −0.6 MPa), was achieved, similar to the results obtained by Centeno et al. (2010). Williams and Trout (2005) and Mirás-Avalos et al. (2014) obtained that midday leaf water potential and stem showed the best results for discriminating between irrigation treatments. In our study, a stem = −0.5 MPa was used as a criteria for irrigation management to the ‘Godello’ cultivar, with a good agreement to discriminate treatments, as referred by Centeno et al. (2010) and Cancela et al. (2015). In contrast, an inefficient schedule for irrigation management was used in DO Rías Baixas, because the vinegrower’s criteria did not take into account neither soil and plant parameters, nor weather conditions (Fig. 3 and 4); even applying higher irrigation depths during the wettest year. However, in DO Valdeorras, stem was as a useful indicator

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Table 3 ˜ and ‘Godello’ grapevines under different irrigation treatments for the 2012, 2013 and 2014 seasons. Yield components and pruning weight of ‘Albarino’ Site and cultivar

Season

Variable

R

DI

SDI

DO Rías Baixas ˜ ‘Albarino’

2012

Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb Yield (kg vine−1 )a Clusters (number vine−1 )a Cluster weight (g)a Pruning weight (kg vine−1 )b Ravaz indexb

3.54 a 52.11 a 62.45 a 2.69 a 1.33 a 6.69 a 67.96 a 97.48 a 1.92 a 3.81 a 5.57 a 47.75 a 117.92 a 3.45 a 2.09 a 2.8 a 22.18 a 130.31 a 0.69 a 4.01 a 3.20 a 21.32 a 142.73 a 0.68 a 4.11 a 2.87 a 22.86 a 122.10 a 0.90 a 3.64 a

3.98 a 55.32 a 69.99 a 2.57 a 1.99 b 7.67 a 74.14 a 103.09 a 1.87 a 4.75 a 5.37 a 45.46 a 116.98 a 3.49 a 1.77 a 2.94 a 19.44 a 144.97 a 0.86 a 3.98 a 3.69 a 20.79 a 170.98 a 0.77 a 5.89 ab 2.72 a 21.36 a 125.02 a 1.11 a 2.49 a

– – – – – – – – –

2013

2014

DO Valdeorras ‘Godello’

2012

2013

2014

– – – – – 3.50 a 21.57 a 152.47 a 0.67 a 5.80 b 4.18 a 26.68 b 152.77 a 0.73 a 6.57 b 2.42 a 19.32 a 117.70 a 0.95 a 3.37 a

The same letter in the row indicates non-significant differences among treatments at p < 0.05. R: rain-fed; DI: surface drip irrigation; SDI: subsurface drip irrigation. a n = 7 vines. b n = 5 vines. Table 4 ˜ and ‘Godello’ musts under different irrigation treatments for the 2012, 2013 and 2014 seasons. Attributes of ‘Albarino’ Site and cultivar

Season

Parameter

R

DI

SDI

DO Rías Baixas ˜ ‘Albarino’

2012

Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 ) Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 ) Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 ) Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 ) Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 ) Probable alcoholic grade (%vol.) Total acidity (g L−1 tartaric acid) pH Tartaric acid (g L−1 ) Malic acid (g L−1 )

13.4 a 9.7 a 3.03 a 7.9 a 4.6 a 12.7 a 7.8 a 3.18 b 5.8 a 4.3 a 10.5 a 12.6 a 3.01 a 6.0 a 8.6 b 13.7 a 6.5 a 3.20 a 5.7 a 4.0 a 14.4 a 6.2 a 3.33 a 6.6 a 2.8 a 12.8 a 7.1 a 3.17 a 8.2 a 3.0 a

13.3 a 10.3 a 2.96 a 7.9 a 4.6 a 12.7 a 8.4 b 3.11 a 6.1 a 4.5 a 10.6 a 12.7 a 3.01 a 6.3 a 8.3 a 13.3 a 7.0 a 3.18 a 4.7 a 3.4 a 14.2 a 6.1 a 3.33 a 6.3 a 2.9 a 12.6 a 7.4 a 3.13 a 8.2 a 3.1 a

– – –

2013

2014

DO Valdeorras ‘Godello’

2012

2013

2014

– – –

– – –

12.9 a 7.9 a 3.14 a 6.3 a 4.1 a 14.1 a 6.9 a 3.26 a 6.8 a 3.1 a 12.6 a 7.9 a 3.06 a 8.6 a 3.2 a

The same letter in the row indicates non-significant differences among treatments at p < 0.05. R: rain-fed; DI: surface drip irrigation; SDI: subsurface drip irrigation.

to determine when to trigger irrigation (Fig. 4). Usually, irrigation depths are scheduled as percentages of ETo , while the ideal would be to apply a calculation method for estimating the required water

amount for each irrigation event according to the objectives (both quantitative and qualitative) of the vinegrower. However, in our experiment, irrigation depth was not evaluated, using a fixed quan-

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107

Table 5 ˜ and ‘Godello’ grapevines under different irrigation treatments for the 2012, 2013 and 2014 seasons. Water productivity indices for ‘Albarino’ WPGrape (kg m−3 )

WPPW (kg m−3 )

WPGrape + PW (kg m−3 )

Site and cultivar

Treatment

2013

2014

2012

2013

2014

2012

2013

2014

DO Rías Baixas ˜ ‘Albarino’

0.996 a R 1.089 a DI Analysis of variance—p-value −1 0.562 Treatment year

1.411 a 1.554 a

1.117 a 0.999 a

0.746 a 0.710 a

0.402 a 0.382 a

0.693 a 0.649 a

1.730 a 1.905 a

1.770 a 2.014 a

1.998 a 1.567 b

0.339

0.411

0.567

0.604

0.652

0.677

0.263

0.042

Treatment Year Treatment * year 4.235 a R 3.412 a DI SDI 3.784 a Analysis of variance—p-value Treatment year−1 0.266

0.654 0.000 0.428 3.669 a 3.638 a 3.923 a

4.551 a 3.708 ab 3.151 b

1.003 a 0.999 a 0.726 a

0.412 0.000 0.964 0.780 a 0.761 a 0.685 a

1.420 a 1.516 a 1.240 a

4.935 a 4.494 a 4.741 a

0.747 0.774 0.128 4.035 a 4.235 a 4.097 a

6.545 a 5.121 a 4.886 a

0.841

0.024

0.118

0.723

0.463

0.849

0.438

0.155

Treatment Year Treatment * year

0.102 0.970 0.208

2012

DO Valdeorras ‘Godello’

0.058 0.000 0.856

0.474 0.056 0.288

The same letter in the column indicates non-significant differences among treatments at p < 0.05. R: rain-fed; DI: surface drip irrigation; SDI: subsurface drip irrigation. WPGrape : water productivity grape yield; WPPW : water productivity pruning weight; WPGrape + PW : water productivity grape yield plus pruning weight.

tity in both experiments, 4.0 and 1.5 h per event (common irrigation time), for DO Rías Baixas and DO Valdeorras, respectively. ˜ These results proved that ‘Albarino’ and ‘Godello’ cultivars present a different behavior in regard to water status (Fig. 4) and suggest that this kind of study must be conducted for each cultivar and cultivation area in order to manage irrigation adequately, as reported by other authors (Basile et al., 2012). In this sense, the current study presents results for two different irrigation schedulings, one managed by the owner of the vineyard and the other one based on climate conditions (soil and plant indices). In fact, the results obtained have been caused not only by the different development of both cultivars but also by the differences in climate (Table 1) and irrigation management between both vineyards. Final objectives of vinegrowers, climate conditions, soil water storage capacity and grapevine cultivar phenology must be accounted for when designing an irrigation strategy for a given vineyard (Dry et al., 2001; Deloire et al., 2004). In both experiments, a trend to lower values of probable alcoholic grade and pH in the musts was observed under irrigation treatments, as well as increases in total acidity (Table 4), as reported by TrigoCórdoba et al. (2015) for another humid region. These results are directly related with vinegrower objectives, total acidity of musts is decreasing in the last years due to climate change; for this reason, irrigation scheduling based on soil and plant indices (DO Valdeorras), allow to obtain higher values (>0.5 g L−1 tartaric acid) of this attribute under the irrigation treatments when compared with the rain-fed treatment (Table 4). Nevertheless, in DO Rías Baixas this trend was not observed clearly for all study years. Moreover, yield and pruning weight were slightly affected by irrigation, causing differences in Ravaz Index between treatments. These results seem to indicate that rainfall amount in both vineyards was enough to fulfill grapevine water requirements, due to the irrigation water amount applied represented a small fraction of TWU. In fact, irrigation water applied was 5% and 23% of the growing season rainfall in DO Rías Baixas and Valdeorras, respectively. Soil texture and AWC were different between the experimental areas, with the lowest AWC value and a sandier texture for DO Rías Baixas. These aspects explain the lower values of WP indices in DO Rías Baixas than in DO Valdeorras, in addition to a higher rainfall amount in the first DO, that could cause leaching of soil nutrients. Moreover, plant density was 2.28 times higher in DO Valdeorras than in DO Rías Baixas, which influenced WP indices, as discussed below.

Water productivity (yield to water consumption ratio) has been proven a useful tool for assessing vine water use under Mediterranean and semi-arid climates (Teixeira et al., 2007; Medrano et al., 2015). However, under Atlantic or humid regions, these indices are less sensitive due to the high vegetative growth of grapevines, which may use rainfall water for vegetative development even at advanced phenological stages and, thus, is related to rainfall distribution over the season (Pereira et al., 2012). Therefore, a simple modification of the WP index is presented here, by including pruning weight into the equation (yield + pruning weight to ˜ vines from DO water consumption ratio: WPGrape + PW ). ‘Albarino’ Rías Baixas showed significant differences between treatments for WPGrape + PW , in 2014. Moreover, the magnitude of the WPGrape and WPPW differed from one year to another. On the contrary, ‘Godello’ vines from DO Valdeorras presented slight differences between treatments showing a trend to achieve greater WPGrape + PW values under the rain-fed treatment, except in 2013. These differences may be due to a higher TWU in the irrigation treatments in DO Valdeorras during the growing season, related to similar soil water contents between treatments and similar yield per treatment, for all years. In general, WP indices were higher for cv. ‘Godello’ in DO Valdeorras, which were related with the total rainfall during the growing season, irrigation scheduling practices, plant density and WUE of cultivar (Pereira et al., 2012; Medrano et al., 2015). Using the data showed by Acevedo-Opazo et al. (2010), we calculated higher values of WPGrape and WPPW for treatments with less irrigation water (18.7 and 8.0 kg m−3 , respectively), for cv. ‘Chardonnay’ in a semi-arid region. A previous study (Trigo-Córdoba et al., 2015) performed in other Galician DO (Ribeiro) showed greater WP values for ‘Godello’ under rain-fed conditions (9.07 kg m−3 ) when compared with a deficit irrigation treatment (6.85 kg m−3 ); however, the plant density was lower (3,333 vines ha−1 ) than that in DO Valdeorras (3800 vines ha−1 ). This is in accordance with the results observed in the current work when only considering grape yield into the calculation of the WP index, and suggests that vines grown in humid regions allocate a relevant amount of resources into vegetative development, showing the relevance of studying irrigation effects on different locations and cultivars (Basile et al., 2012). Otherwise, WPPW values, calculated from Trigo-Córdoba et al. (2015), showed for rain-fed treatment an average value of 2.42 kg m−3 , higher than the average value for DO Valdeorras, 1.07 kg m−3 (Table 5). From the information collected in Intrigliolo et al. (2012), we obtained

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an intermediate value to WPGrape for rain-fed (2.87 kg m−3 ) cv ‘Tempranillo’ (1666 vines ha−1 ), than those obtained for rain-fed ˜ in Galicia (Table 5). Moreover, data from ‘Godello’ and ‘Albarino’ Intrigliolo et al. (2012) showed a WPPW for rain-fed (0.58 kg m−3 ) lower than that in our cultivars and locations. These last examples justify the relevance of taking into account not only irrigation water applied but also location, cultivar and cultural practices; using both vegetative growth (pruning weight) and yield (grapes) field measures, to achieve WP indices comparable between regions and cultivars. This would aid in making decisions for irrigation scheduling.

5. Conclusions Modifications of WP indices for grapevines were performed by including pruning weight into the equations. This allowed us to ˜ and ‘Godello’) better describe water use in two cultivars (‘Albarino’ from two different DO (Rías Baixas and Valdeorras) in Galicia, a humid region of NW Spain. Irrigated ‘Godello’ vines presented less ˜ negative stem water potentials than those rain-fed but ‘Albarino’ water status was unaffected by irrigation. Since no significant differences were observed in yield parameters, we consider that water supplied by rainfall was sufficient for adequate plant functioning. Must quality was slightly affected by irrigation. WP was similar between treatments but greater in rain-fed ‘Godello’ vines when only grape was considered into the calculation of this index. Due to the fact that irrigation management was different for both cultivars, based on soil and plant indicators (stem ) measured for ‘Godello’, we concluded that climate, soil, cultivar phenology and vinegrower’s objectives must be carefully considered for scheduling irrigation. Under the global change context and accounting for the water scarcity scenario that must be faced, the results obtained in this study proved that a rational management of irrigation can be achieved by combining soil and plant water status measurements, and we provide a new tool for assessing vine water use that allows for comparisons between regions and cultivars (WPPW and WPGrape + PW ). Acknowledgements This research was supported by the Spanish Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Project n◦ RTA2011-00041-C02-00, with 80% FEDER funds. J.M. MirásAvalos and E.M. Martínez thank Xunta de Galicia for funding their contracts through the “Isidro Parga Pondal” and “Isabel Barreto” Programmes. E. Trigo-Córdoba and Y. Bouzas-Cid thank INIA for their PhD scholarships (FPI-INIA). Thanks to NaanDanJain Iberica, SL for providing irrigation pipes and emitters.

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