Estimation of water requirements and Kc values of ‘Thompson Seedless’ table grapes grown in the overhead trellis system, using the Eddy covariance metho

Abstract

Crop evapotranspiration (ETc) is essential for irrigation scheduling. The amount of water consumed can be estimated by multiplying the reference evapotranspiration (ET0) by a crop coefficient (Kc); the value of Kc is usually obtained from FAO Paper nr 56. In table grapes (Vitis vinifera L.), Kc are obtained from experiments in vines trained on trellis systems; however in Chile, the most used is the overhead trellis system (parronal). Therefore, the objective was to determine water requirements and Kc values of a table grape orchard cv. Thompson Seedless trained on an overhead trellis system in Calle Larga (32 degrees 52 ' 40" S, 70 degrees 37 ' 45" W, 795 m a.s.l.), Aconcagua Valley, Chile, using the Eddy covariance method. During the 2008/2009 and 2009/2010 seasons, the instruments required for ET0 and ETc measurement were installed on a 4 m tower above the soil (2 m above vine canopy). The ET0 was estimated according to the FAO Penman-Monteith equation and ETc by the Eddy covariance method. The Kc was obtained by ratio between ETc and ET0. The maximum ETc was 7 mm d(-1) and total water consumption was 810 mm. The season maximum Kc value of 1.2 was obtained near harvest during the first season, and 20 d before veraison in the second season. The Kc increased linearly with the percentage of intercepted solar radiation (IRS) by the vine canopy at noon, suggesting that an equation to convert the IRS to Kc is more useful than Kc tabulated according to phenology. The equation obtained in this experiment was Kc = 0.012 IRS - 0.1029, R-2 = 0.85.

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213212 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
Estimation of water requirements and Kc values of ‘Thompson Seedless’ table
grapes grown in the overhead trellis system, using the Eddy covariance method
Paulina Villagra,1 Víctor García de Cortázar2, Raúl Ferreyra1, Cristina Aspillaga1, Carlos Zúñiga1,
Samuel Ortega-Farias3, and Gabriel Sellés1*
Crop evapotranspiration (ETc) is essential for irrigation scheduling. The amount of water consumed can be estimated by
multiplying the reference evapotranspiration (ET0) by a crop coefcient (Kc); the value of Kc is usually obtained from
FAO Paper nr 56. In table grapes (Vitis vinifera L.), Kc are obtained from experiments in vines trained on trellis systems;
however in Chile, the most used is the overhead trellis system (parronal). Therefore, the objective was to determine water
requirements and Kc values of a table grape orchard cv. Thompson Seedless trained on an overhead trellis system in Calle
Larga (32º52’40” S, 70º37’45” W, 795 m a.s.l.), Aconcagua Valley, Chile, using the Eddy covariance method. During the
2008/2009 and 2009/2010 seasons, the instruments required for ET0 and ETc measurement were installed on a 4 m tower
above the soil (2 m above vine canopy). The ET0 was estimated according to the FAO Penman-Monteith equation and
ETc by the Eddy covariance method. The Kc was obtained by ratio between ETc and ET0. The maximum ETc was 7 mm
d-1 and total water consumption was 810 mm. The season maximum Kc value of 1.2 was obtained near harvest during the
rst season, and 20 d before veraison in the second season. The Kc increased linearly with the percentage of intercepted
solar radiation (IRS) by the vine canopy at noon, suggesting that an equation to convert the IRS to Kc is more useful than
Kc tabulated according to phenology. The equation obtained in this experiment was Kc = 0.012 IRS – 0.1029, R2 = 0.85.
Key words: Energy balance, evapotranspiration, FAO Penman-Monteith, Vitis vinifera.
1Instituto de Investigaciones Agropecuarias, INIA La Platina, Santa
Rosa 11610, Santiago, Chile.
*Corresponding author (gselles@inia.cl).
2Universidad de Chile, Facultad de Ciencias Agronómicas, Santa
Rosa 11315, Santiago, Chile.
3Universidad de Talca, Facultad de Ciencias Agrarias, Av. Lircay s/n,
Talca, Chile.
Received: 17 October 2013.
Accepted: 14 April 2014.
doi:10.4067/S0718-58392014000200013
INTRODUCTION
The assessment of crop evapotranspiration (ETc) allows
adjusting the water volume applied and irrigation
frequencies to the effective needs of the crop, which
increases irrigation efciency. Unfortunately, ETc
measurements for adult fruit trees are scarce (Williams et
al., 2003b; García Petillo and Castel, 2007), even though
the study of the processes of ETc can help model, predict,
and increase crop yields (Moguel et al., 2001).
The ETc may be estimated based on studies of soil
water balance in cultivated elds (Allen et al., 1998),
by weighing lysimeters (Allen et al., 1998; Williams et
al., 2003b; Williams and Ayars, 2005a), by method of
mass transference or energy balance (Allen et al., 1998;
Moguel et al., 2001; Teixeira et al., 2007; Conceição et
al., 2008; Giambelluca et al., 2009), or Eddy covariance
RESEARCH
method (Martín de Santa Olalla y de Juan, 1993; Gomes,
2003; Paço et al., 2004; Barr et al., 2006; Conceição et
al., 2008; Giambelluca et al., 2009) or using reference
evapotranspiration (ET0) weighted by a crop coefcient
(Kc) (Allen et al., 1998; Ferreira et al., 2006).
Selecting the appropriate value of Kc, which should
be used in a given moment, is not an easy task (Sellés
et al., 2000). In the case of table grapes, Kc values have
been estimated in trellis system not in an overhead trellis
system, as table grapes are cultivated in Chile. In the last
30 yr many studies have estimated standard values and
the temporal evolution of crop coefcients. However,
it is always recommended to adapt them to the local
climate, varieties, and management practices, especially
in fruit crops, in which standard parameters may vary
considerably from one area to another (Campos et al.,
2010). Studies in citrus (Castel, 1997; García Petillo and
Castel, 2007), apricot (Paço et al., 2004), pear (Conceição
et al., 2008), and kiwi orchards (Silva et al., 2008) show
that the Kc values obtained experimentally in local
conditions may not be concordant with those proposed by
FAO 56 (Allen et al., 1998).
The only Kc values available in the literature for
table grapes come from lysimeter studies performed in
California at orchards using the trellis system (Allen et
al., 1998; Williams et al., 2003a; 2003b) and Williams and
Ayars (2005a; 2005b).

215214 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
There are almost no studies in Chile on table grape (Vitis
vinifera L.) evapotranspiration. Tosso (1976) and Tosso
and Torres (1986) estimated Kc values for table grape.
However, the methodology used was not the most exact
and only its utility for future research was considered, with
values that should be conrmed or corrected. The most
frequently used source are the Kc values proposed in FAO
paper nr 56 (Allen et al., 1998) where Kc values for table
grapes are tabulated according only to the phenological
stages without consideration of training systems. In the
USA the trellis system is of widespread use in table
grape crops and hence, FAO56 uses this training system
for its recommendations. In Chile, by contrast, the most
common system is the overhead trellis. Thus the objective
of this study was to determine ETc and Kc in different
phenological stages of ‘Thompson Seedless’ table grapes
grown in overhead trellis. Additionally, the Kc values
obtained were correlated with solar radiation interception
to obtain a simple method of Kc estimation.
MATERIALS AND METHODS
Experimental site
The experiments were performed in a commercial
vineyard of ‘Thompson Seedless’ table grapes grafted
on ‘Harmony’ rootstock (8-yr old), and conducted on
an overhead trellis system, located in Valparaíso Region
(32°52’40” S, 70°37’45” W, elevation 795 m a.s.l.),
Chile; during 2008-2009 and 2009-2010 seasons. Trials
were performed in the central part of a 150 ha eld
planted with table grapes in overhead trellis. The study
zone had a surface area of 7 ha; grapes were planted at
3.5 × 1.75 m. Drip irrigation was used, with one line per
plant row and 4 L h-1 emitters spaced at 1 m. The yield
of the plantation in the last 3 yr averaged 28 t ha-1. The
soil is a Fluventic Haploxerolls (Mollisol), 1 m depth,
with a clay loam texture in all depths. The climactic
conditions (monthly average temperature, rainfall, and
pan evaporation) during the study period are presented
in Table 1.
Soil water content measurement
The variation in soil water content was measured
continuously in both seasons, using one FDR probe
(Frequency Domain Reectometry, Agrilink, AquaSpy,
San Diego, California, USA), placed near the tower, with
sensors at 10, 20, 30, 40, 50, 60, 80, and 100 cm depth.
Determination of intercepted solar radiation
To determine the solar radiation intercepted by the table
grape orchard we measured, every 2 wk, the ux density
of photosynthetically active incident radiation over
(PARi) and under the orchard (PARbd) with a ceptometer
(AccuPAR, Decagon Devices, Washington, USA).
Data were measured in six quadrants of six plants each
(three plants per row) in the experimental area. Fifteen
measurements were made for each quadrant; ve in each
row and ve between rows. Measurements were made at
solar zenith every 2 wk. Mean values in μmol photons
m-2 s-1 were expressed as percentages using:
where IRS is the percentage intercepted solar radiation,
PARbd is the ow of photosynthetically active radiation
under the vines and PARi is the ow of photosynthetically
active radiation above the vines, both measured in μmol
photons m-2 s-1.
Measurement of energy balance components and crop
evapotranspiration
The sensible heat ux (H) and the latent ux (LE) were
measured with the method of Eddy covariance. To do this,
a 4-m tower (2 m above the crop) with a sonic anemometer
(Windmaster Pro, Gill Instruments, Hampshire, UK)
and an open pass gas analyzer of CO2/H2O (OP-2, ADC
Bioscientic Ltd., Hoddesdon, UK), oriented in the
dominant wind direction (SW), were installed. Fetch length
for the dominant wind was 250 m and it was at least 100
m in every orientation. The frequency of measurements
was 10 Hz averaged over 30 min. Data were recorded on
a CR-1000 datalogger (Campbell Scientic Inc., Logan,
Utah, USA). The processing of data and corrections
°C mm m-1 °C mm m-1
May 13.20 65.8 51.0 13.9 0.8 46.1
June 10.80 34.3 27.8 10.4 89.2 25.1
July 9.40 27.8 31.0 9.8 13.0 32.4
August 10.90 87.0 38.0 11.8 69.8 36.4
September 13.70 12.0 78.8 12.0 10.4 58.2
October 16.20 129.0 17.3 135.3
November 20.20 175.5 17.7 161.9
December 21.40 210.3 20.4 222.0
January 22.40 231.1 21.7 217.7
February 21.33 186.0 20.7 169.9
March 20.80 169.0 19.7 123.2
April 18.00 114.6 15.9 80.3
Table 1. Monthly average temperature, rainfall and pan evaporation during 2008/2009 and 2009/2010 season.
Month
2008/2009 season
Monthly average
temperature
Monthly
rain
Monthly pan
evaporation
2009/2010 season
Monthly average
temperature
Monthly
rain
Monthly pan
evaporation
ISR = PARbd
PARi
( )
1–·100

215214 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
Figure 1. Variation in water content (h) in the soil prole during the 2008-2009 (above) and 2009-2010 (below) seasons. Dashed lines indicate
eld capacity (FC) and watering threshold (70% AW).
were done with the software Eddysoft (Meteotools, Max
Planck Institut für Biochemie, Germany). Latent ux
was corrected as proposed by Webb et al. (1980); for H
corrections proposed by Schotanus et al. (1983) and Liu
et al. (2001) were used. The crop evapotranspiration
was derived from LE, dividing LE by the latent heat of
vaporization of water (2.44 MJ kg-1). The footprints for
the two seasons were 34 m for 50% and 230 m for 90%.
Net solar radiation (Rn) was measured with a net
radiometer (NR2, Delta-T Devices, Cambridge, UK)
installed in the same tower. We also installed in the
ground two soil heat ux plates (HFP01, Hukseux
Thermal Sensors, Delft, The Netherlands) at 7 cm depth,
one over the row at 3.5 m from the tower and the other
in the next row. To determine the heat ow in the soil
(G) we measured the absorption or liberation of heat in
the soil above the plates with four copper-constantan
thermocouples; two above the row and two in the next
row, at 2 and 6 cm depth, which measured the variation in
soil temperature.
The values of LE, H, G, and Rn were used to verify
the closure of the energy balance and thus validate the
Eddy covariance measurements. Measurements may
be considered valid when the closure error does not
exceed 20% (Wilson et al., 2002). Linear regressions
of the energy used in heat transport (LE + H) against
the effective amount of energy available (Rn - G) were
estimated. The closure error of each regression, expressed
as a percentage, was calculated as 100 × (1 - slope).
Calculation of reference evapotranspiration and Kc
values
Reference evapotranspiration was calculated with the
Penman-Monteith FAO equation (Allen et al., 1998); thus
in the instrument tower we also measured net radiation
(NR2, Delta-T Devices, UK), temperature (T), relative air
humidity (HR) (humidity and temperature probe HMP50,
Intercap, Vaisala, Vantaa, Finland), and wind velocity
(u) (wind sensor WM-IIIA, Climatronics Corporation,
Bohemia, New York, USA). All these measurements were
done every 30 min.
Crop coefcient values were calculated weekly as
the quotient between the average ET measured by eddy
covariance and the average ET0.
RESULTS AND DISCUSSION
Soil water content and intercepted solar radiation
Soil water content at eld capacity (FC) was 280 mm m-1.
The mean water content during the period was 276 mm
m-1 (Figure 1). The water in the prole remained close to
FC in both seasons. This assures that plants did not have
water decit, thus stomata were completely open and

217216 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
transpiring at their maximum potential. Possible problems
of aeration provoked by the high soil water content were
discounted, since the commercial yield of the orchard (28
t ha-1) and the condition of the plants did not indicate any
symptom related to excess soil water.
Figure 2 shows the variation in IRS during the season.
Both seasons had similar behavior, at the moment of berry
set the IRS was around 75%; the maximum IRS (112 d
after bud break, DAB) occurred close to veraison.
Energy balance components, crop evapotranspiration,
and crop coefcient
The closure error of energy balance was close to 40% from
bud break until vines intercepted 40% of solar radiation
(45 DAB). The closure error decreased as the season
advanced and leaf area increased, which is reected in
closing errors less than 20% after IRS reached 40%. At
the end of the season, this error reached 2% (Figure 3). As
a consequence, measurements may be accepted as valid
from the time the vines intercepted 40% of solar radiation,
since that moment on the closure error did not exceed the
20% limit, proposed by Wilson et al. (2002) for validation
of measurements using the Eddy covariance method.
Figure 4 shows that in the rst season ETc was less than
ET0 from bud break to 147 DAB. From this day until 167
DAB, the ETc was greater than ET0. From 168 DAB to
the end of the growth period ET0 was again greater than
ETc. In the second season, from bud break to 90 DAB
ETc was less than ET0. From 91 DAB until 112 DAB ETc
was greater than ET0. Mean maximum ETc (Figure 4) in
both seasons was 7 mm d-1, which is very close to the
values reported for the same variety by Williams et al.
(2003a) and Williams and Ayars (2005a; 2005b), which
were 6.6, 6.75, and 6.99 mm d-1, respectively. Total water
consumption (810 mm) was also similar to the values
reported in these studies.
The maximum calculated Kc in both seasons was 1.2
(Figure 5); however, this was reached in different stages.
In the rst season it occurred close to harvest, while in the
second season it happened 20 d after veraison. Comparing
our results to the proposal of FAO Paper nr 56 (Allen et al.,
1998) (hereafter called FAO Kc values), in the rst season
the FAO Kc values underestimate local water needs of
‘Thompson Seedless’ grapes between 28 and 84 DAB,
and beginning with 140 DAB. According to the values
we obtained in the second season, local Kc values were
underestimated by the tabulated FAO Kc values from 28
DAB until the end of the season. Because of the variation
found, Kc was estimated using the values obtained in both
seasons (Eddy, Figure 5), with the following result:
where, Kc is the crop coefcient and DAB is days after
bud break.
If the values published in FAO Paper nr 56 are used
to calculate the ETc, the real water consumption of table
grapes would be underestimated in the trial conditions
from 28 DAB onwards. The maximum Kc value would
Figure 2. Intercepted solar radiation by the plantation during the
2008-2009 and 2009-2010 seasons. Arrows indicate the times of berry
set, veraison, and fruit harvest.
**Highly signicant regressions (p < 0.01).
Rn: net radiation; G: soil heat ux; LE: latent heat ux; H: sensible heat
ux.
Figure 3. Energy balance closure with different percentages of solar
radiation intercepted by the orchard (0-40%, 300 data; 40-80% 560
data; > 80%, 1020 data). The closure error of each regression is
represented as 100 × (1 - slope).
(1 + 0.54e –0.05DAB),
Kc =1.07 R2 = 0.84

217216 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
be obtained at 155 DAB, close to the date of harvest, and
would be approximately 1.05. We suggest that values
proposed in the FAO paper (Allen et al., 1998) do not
represent the local crop conditions for table grapes
grown in an overhead trellis system. This has also been
observed by other authors on other species; Castel (1997)
reported that values obtained for clementines were about
20% lower than the FAO Kc values, while Paço et al.
(2004) found that ETc was overestimated by 35% by the
Figure 4. Seven-days averages of crop evapotranspiration (ETc) of the
grape orchard and of reference evapotranspiration (ET0) during the
2008-2009 (above) and 2009-2010 (below) seasons. The blank spaces
in data indicate periods of malfunctioning of the sonic anemometer.
Figure 5. Comparison of crop coefcient (Kc) values calculated
in two seasons (Eddy 2008-2009, Eddy 2009-2010) with the values
proposed in FAO Paper nr 56 (Allen et al., 1998). Also shown are
Kc values adjusted to the data (Eddy) for both study seasons using
days after bud break (DAB). Arrows indicate the times of berry set,
veraison, and fruit harvest.
Figure 6. Relation between calculated crop coefcient (Kc) and
percentage of solar radiation intercepted by the grape orchard during
the 2008-2009 and 2009-2010 seasons. Kc is the weekly average
around the date of measurement of solar radiation interception
which was measured every 15 d.
FAO Kc values for peach compared to those measured
using the Eddy covariance technique in a peach orchard
in Portugal. Also in Portugal, Conceição et al. (2008)
conrmed the need to adjust published values for a pear
orchard.
The Kc values obtained for different phenological
stages and for DAB were different between the two
seasons. For this reason, we analyzed the calculated Kc
with the percentage of IRS on the same dates (Figure 6).
The linear relation obtained is similar to that obtained in
‘Thompson Seedless’ with the trellis system by Williams
and Ayars (2005a); their equation had a slope of 0.017 and
an intercept of -0.008. The same linear relation between
Kc and IRS has been reported in bananas (Santana et al.,
1993), clementines (Castel, 1997), peaches (Johnson et
al., 2000; Goodwin et al., 2006), and olives (Testi et al.,
2004). Intercepted solar radiation explained 85% of the
variation in water consumption by the orchard (Figure
6), and its relation with Kc appears to be very general
(Johnson et al., 2000). This would explain why local
conditions are not well represented by the FAO Kc values,
which were derived from studies of table grapes using the
trellis system, were the IRS is lower than overhead trellis
system. Since the percentage of solar radiation intercepted
by grapevines may vary according to the training system,
plantation spacing and pruning, it is unlikely that the
same Kc values will be found in table grapes cultivated
with different agricultural management systems. Since
IRS is a parameter easy to measure, Kc may be estimated
at different ages in any locality and in plantations with
different management systems, simplifying the prediction
of ETc. This suggests that, instead of relying on tables
with Kc for each phenological state or for DAB, it is more
useful to have an equation which converts the percentage
of IRS into a Kc value. The equation we obtained using
measurements of two seasons, which is valid above 20%
interception, is:
Kc = 0.012 · IRS – 0.1029, R2 = 0.85
where Kc is the crop coefcient and ISR is the percentage
of intercepted solar radiation.

219218 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 74(2) APRIL-JUNE 2014
CONCLUSIONS
Water requirements of ‘Thompson Seedless’ table grapes
grown in overhead trellis may be estimated using the
Eddy covariance method with reasonable precision. The
value of Kc increased linearly with the percentage of
solar radiation intercepted by the table grape orchard.
The results suggest that knowledge of the percentage
interception of solar radiation is more important than the
phenological stage to determine the value of Kc, since
the former takes into account the local conditions of crop
management.
ACKNOWLEDGEMENTS
The authors thank INNOVA Project nr 05-CR11PAT-11
“Increasing the Productivity of Table Grapes” for
nancing this study.
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