2017 Oregon Wine Symposium | Dr. Larry Williams- Coping Strategies for a Warmer Climate: Irrigation and Canopy Management

2017 Oregon Wine Symposium
Coping Strategies for a Warmer
Climate : Irrigation/Canopy
Management
Larry E. Williams
Kearney Agricultural Research and Extension Center
and
Department of Viticulture and Enology
UC-Davis

Vineyard Irrigation Strategies should be
knowledge based:
• What is vineyard ETc or do you have an estimate of
ETc?
• How much water is actually applied each year? How is
that measured?
• How much water in the soil profile is available for
consumptive water use? Do you have a means to
determine that amount or asses vine water status?
• How does vineyard design (row spacing and trellis
type) affect vineyard ETc?
• What fraction of seasonal ETc is used between
budbreak and bloom, veraison or harvest?
• Can RDI or SDI be used to minimize water use while
maintaining yields of high quality?

Performance Metrics and the
California Sustainable
Winegrowing Program:
“You can’t manage what you
don’t measure”
California Sustainable
Winegrowing Alliance

Within the drip line water meter.

Important irrigation management decisions
• When should one initiate irrigations at the
beginning of the season?
• How much water should one apply?
• How does the design of your irrigation
system affect the ability to irrigate your
vineyards?
• How reliable is your water supply?
• Are there deficit irrigation practices to
minimize production loss and maximize
fruit quality?

2017 Oregon Wine Symposium
Coping Strategies for a Warmer Climate: Irrigation/Canopy
Management
Vineyard Irrigation Scheduling - Basics
Larry E. Williams
Department of Viticulture and Enology
University of California-Davis
Kearney Agricultural Research and Extension Center
9240 S. Riverbend Ave., Parlier CA 93648
lewilliams@ucanr.edu

“Goal of irrigation management”
Mark Battany
• Your goal should be to grow vines with a uniform
degree and pattern of water stress every season
(the degree of stress determined by the grower).
• To do this, you need to adjust irrigation timing
and amounts to take into account unique growing
conditions in any given season.
• Weather (evaporative demand and temperature)
is the variable component that exerts the most
influence on irrigation requirements during the
season.

ETc = ETo x Kc
The above equation estimates
vineyard water use at 100% of ETc.
ETo is reference ET (measure of
evaporative demand at a location).
This takes into account the weather
factors. The Kc is defined in the
next slide.

Crop Coefficient (Kc)
• The fraction of water used by a specific
crop compared to that of ETo at a given
location
• Kc = ETc / ETo
• The Kc depends upon stage of crop
development, degree of cover, crop height
and canopy resistance.
• Calculated as a function of degree-days

Reliable crop coefficients should take
the following into account:
• Seasonal growth of grapevines
• Final canopy size, which is a function of
trellis design
• Row spacing (the closer the row spacing
the greater the water use per acre)
• Possible differences in growth (canopy
size) due to cultivar and/or rootstock

One can get a reliable estimate of the
seasonal crop coefficient for
vineyards by measuring the amount
of shade cast on the ground beneath
the canopy around solar noon
throughout the growing season. The
equation is:
Kc = 0.017 * % shaded area
(% shaded area is measured shaded area per vine divided by area per vine
in the vineyard)
(percent shaded area is a whole number)
(Williams and Ayars (2005) Agric. For. Meteor. 132:201-211)

Trellis/ Row Spacing
Canopy type (m) Crop coefficient equation
VSP 1.83 (6 ft.) Kc = 0.87/(1+ e(-(x – 525)/301))
2.13 (7 ft.) Kc = 0.74/(1+ e(-(x – 525)/301))
2.44 (8 ft.) Kc = 0.65/(1+ e(-(x – 525)/301))
2.74 (9 ft.) Kc = 0.58/(1+ e(-(x – 525)/301))
3.05 (10 ft.) Kc = 0.52/(1+ e(-(x – 525)/301))
CA Sprawl 3.05 (10 ft.) Kc = 0.84/(1+ e(-(x – 325)/105))
3.35 (11 ft.) Kc = 0.76/(1+ e(-(x – 325)/105))
3.66 (12 ft.) Kc = 0.70/(1+ e(-(x – 325)/105))
Quad-cordons 3.35 (11 ft.) Kc = 0.93/(1+ e(-(x – 300)/175))
(or GDC/Wye) 3.66 (12 ft.) Kc = 0.85/(1+ e(-(x – 300)/175))
Lyre Types 2.74 (9 ft.) Kc = 0.93/(1 + e(-(x – 300)/150))
or ‘V’ 3.05 (10 ft.) Kc = 0.84/(1 + e(-(x – 300)/150))
3.35 11 ft.) Kc = 0.76/(1 + e(-(x – 300)/150))
3.66 (12 ft.) Kc = 0.70/(1 + e(-(x – 300)/150))
The effect of row spacing on estimated seasonal Kc values for a VSP trellis system, a California Sprawl
type canopy, quadrilateral cordon trained vines and Lyre type canopies. The x value in the equation is
degree-days (base of 10oC) from a starting point. The e value in the equation is 2.71828. Note that row
spacing only changes the numerator in the equation, the maximum Kc value.

Possible topics covered:
• How to deal with less than full soil moisture
profile at beginning of season
• When best to initiate irrigation
• How best to monitor plant water status and
soil moisture
• How to design irrigation strategies for different
soil profiles and is it better to irrigate deeply
and infrequently or more frequently and
shallower
• How to deal with heat spikes
• How to deal with the possibility of losing water
supply before harvest.

Vineyard
evapotranspiration:
ETc 101
‘The Basics’

Definitions
• Transpiration – evaporation of water that has
passed through a plant
• Stomatal conductance – a measure of how open or
closed the stomata are
• Crop evapotranspiration (ETc) – the total process of
water transfer to the atmosphere by a specific crop
(i.e. grapevines) to include soil evaporation
• Reference ET (ETo) – a measure of the evaporative
demand in a region (can be obtained from CIMIS)
• Leaf water potential – a measure of the water status
of plants (units expressed in bars or megapascals
(MPa), 10 bars = 1.0 MPa)

Calculation of Evapotranspiration (ET)
Δ (Rn – G) + ρcpδe/ra
Ep = __________________________
Δ + γ (1 + rc/ra)
Δ = temp. derivate of saturated vapor pressure function (Pa K-1)
Rn = net radiation (W m-2)
G = rate of change of energy storage (W m-2)
ρ = density of dry air (1.2 kg m-2)
 = latent heat of vaporization (2465 J g-1)
cp = specific heat of the air at constant pressure (1005 J kg-1 K-1)
δe = vapor pressure deficit (Pa) (as RH decreases VPD increases)
ra = aerodynamic resistance (s m-1)
γ = psychrometric ‘constant’ (66 Pa K-1)
rc = canopy resistance of stand (s m-1)

Environmental Factors Affecting ET
• As Net Radiation increases, ET
increases (it is the driving force
of ET)
• As the VPD increases (or as RH
decreases), ET increases
• As wind increases, ET increases

7 July, 1993
14.7 gal/day
max/hr
1.76 gal
No nighttime transpiration 

Field Capacity
Permanent Wilting
Point
Completely Dry
Available
Soil
Moisture
Readily Available WaterB
Illustration of Soil Moisture TermsA
A At soil saturation the beaker would be full or overflowing.
B Readily available water is considered to be ~50% of the available soil moisture.

Soil water content measured directly beneath the drip line to a depth of 5½ feet.

Readings were taken at depths of 0.23, 0.46, 0.76,
1.07,1.37 and 1.67 m (9, 18, 30, 42, 54 and 66
inches, respectively) from the soil surface.
Grapevinewateruse/evaporativedemand

12.1 gal/day
13.1 gal/day
4.52 gal/day
3.68 gal/day
transient cloud
cover
Dr. Vinay Pagay – estimated that
32% of daily total water use was
from transpiration occurring at
night for Tempranillo vines
grown in southern Oregon.

20 Jul 23 Jul 26 Jul 29 Jul 01 Aug 04 Aug 07 Aug
SapFlowVelocity(cmhr
-1
)
0
20
40
60
80
100
HRM
CHPM 18
CHPM 24
CHPM 36
Irrigation event
Sap flow velocity of Thompson Seedless grapevines in response to
the termination of irrigation. Irrigation was terminated 11 July and
irrigated again on 6 August for 3 hours (~20 gallons/vine).

Vineyard ETc is a function of the amount of light
intercepted by the canopy (also called fraction
of ground cover or % shaded area).
• As the canopy develops (becomes
larger) during the season, vineyard
water use increases.
• As the trellis width increases the amount
of canopy intercepting light increases
therefore, water use increases.
• The closer the row spacing the greater
the water use per unit land area.

% shaded area is also called fraction of canopy cover

What percentage of ETc is due to vine
transpiration? How much water is lost via
soil evaporation?
Vine water use, measured with the
weighing lysimeter, was compared when
the soil surface was covered with two
layers of thick plastic versus no plastic
on the soil surface. This was done over
several years under high frequency drip
irrigation at 100% of ETc.

Lysimeter covered with
plastic to minimize soil
water evaporation.

What percentage of ETc is E or soil
evaporation?
• Lysimeter’s soil surface was covered with
plastic numerous times during the 2009
growing season (6 June to 14 Sept.).
• Grapevine water use was reduced ~ 11%
when the soil was covered with plastic
compared to bare soil (5.64 vs. 6.36
mm/day).
• The Kc was reduced from an average of
1.07 to 0.93 (13% reduction) over the 100
day period mid-season.

How to deal with less
than full soil moisture
profile at the beginning
of the season. Is it a
problem?

Dry soil at budbreak: possible
consequences
• Delayed shoot growth
• Abscission of clusters
• Reduced yield (due to smaller berries and
fewer clusters)
• “Effect of winter rainfall on yield components
and fruit green aromas of Vitis vinifera L. cv.
Merlot in California” Mendez-Costabel et al. (2014)
Austral. J. Grape Wine Res. 20:100-110.
• Irrigation wasn’t initiated until 22 and 16 May
in 2009 and 2010, respectively.

Soil water content as
a function of irrigation
treatment in a Thompson
Seedless vineyard (soil water
content at field capacity is ~22% v/v.)
Rainfall dormancy:
11/90 → BB/91 = 299* mm (11.8 in)
11/91 → BB/92 = 241 mm (9.5 in)
11/92 → BB/93 = 350 mm (13.8 in)
Δ Soil water content
11/90 → BB/91= 150 mm (5.9 in)
11/91 → BB/92 = 138 mm (5.4 in)
11/92 → BB/93 = 198 mm (7.8 in)
Upward arrows indicate date
irrigation commenced each year.
*From the 1st to end of March
(222 mm rainfall)
FC
FC

Shoot length as a function of day
of year across three years. Note
that delayed shoot growth only
occurred early on in 1991 for the
treatment irrigated at 20%
of ETc despite soil water content
for that treatment, compared to
the other three treatments. Clusters
also abscised for the 0 and 20%
ETc treatments.
*Soil matric potential for the 0.2
irrigation treatment = -76 cbar.
Same value in 1992 at same date.
*

Shoot lengths from 1991 as a function of degree-days from
budbreak. The numbers next to a data point represent the
midday leaf water potential for a particular treatment (MPa)

Question: How much does rainfall (dormant
and in-season) contribute to the water
requirements of a vineyard in the San Joaquin
valley?
Possible Answer:
The evaporation of water from the soil after a
rainfall event can approach ETo for up to three
days (~ 5 mm (0.2 in.) per day determined with a
weighing lysimeter early in the spring). Most
researchers assume that 50% of the rainfall is
effective (depending upon a few more factors).
Therefore, if you receive 25 mm (1 inch) of rain,
you can assume ½ of that is available for the
grapevines.

Soil water balance can be calculated as follows:
P + I + W – ETc – R – D = + ΔSWC
where P is precipitation, I is irrigation amount, W is the
contribution of a water table via upward capillary flow,
ETc is vineyard ET, R is surface runoff, D is drainage
and ΔSWC is the change in soil water content
between measurement dates. Effective daily rainfall:
Effective rainfall (mm) = (rainfall amount – 6.35) x 0.8
(Prichard et al., 2004)
Williams (2014, Amer. J. Enol. Vitic. 65: 159-168) has
found this to be reliable for rainfall during the growing
season.

Rainfall amounts and the change in soil water content from 1
November to budbreak the following year in a vineyard at the
Kearney Agricultural Research and Extension Center near
Parlier. The soil was a Hanford fine sandy soil. Soil water
content was measured to a depth of 2.9 m in plots irrigated at
0.2, 0.6, 1.0 and 1.4 times vine water use. ETo averaged 166
mm during dormancy. (vine and row spacing = 7x11ft.)
Rainfall during dormancy:
11/90 → BB/91 = 299 mm (11.8 in)
11/91 → BB/92 = 241 mm (9.5 in)
11/92 → BB/93 = 350 mm (13.8 in)
11/93 → BB/94 = 165 mm (6.5 in)
11/94 → BB/95 = 447 mm (17.6 in) Calculated
Δ Soil water content: Effective rainfall
11/90 → BB/91 = 150 mm (50%) 138 mm (275 gal/vine)
11/91 → BB/92 = 138 mm (57%) 110 mm (220 gal/vine)
11/92 → BB/93 = 198 mm (57%) 167 mm (333 gal/vine)
11/93 → BB/94 = 61 mm (37%) 45 mm (90 gal/vine)
11/94 → BB/95 = 181 mm (40%) 192 mm (383 gal/vine)

Question: How deep in the soil
profile do grapevines use
water and what fraction of ETc
is with water derived from the
soil profile?

Access tube arrangement for Thompson Seedless vines with 2.15 m between vines and
3.51 m between rows. Tube depth is 3 m with nine tubes per site.

Chardonnay vineyard,
Carneros region in
Napa Valley (clay
loam soil).

Kearney Ag Center
(vines were drip irrigated
multiple times daily at the
fraction of measured ETc
given in the graph)
SWC directly below
the in-row emitters.

Question: How much water do
grapevines use? Differences in
water use among vineyards:
effects of canopy type and row
spacing.

Several canopy types in Viticulture

Scarlet Royal vineyard on 16 September, 2014. (3.05 m (10 ft.) rows)

Estimated seasonal water use (ETc) for various
trellises on an 11-foot row spacing using
historical DDs and ETo data.
• Open gable trellis: 1,200 mm (47.2 in.)
• Two foot crossarm (Lysimeter): 907 mm
(35.7 in.)
• Vines w/quad cordons: 912 mm (35.9 in.)
• CA sprawl: 785 mm (30.9 in.) (34 in. for 10 ft.
row or 28 in. for 12 ft. row)
• Lyre type trellis: 779 mm (30.7 in.)
• VSP: 552 mm (21.7 in.)

Year Irrigation Soil Applied
(rain) Treatment Yield H2O H2O ETc
(t/acre) (mm) (mm) (mm)
1998 0 6.99 260 0 260 (10.2 in)
(35.5 in) 0.5 7.52 201 (66%) 105 306 (12.0 in)
1.0 7.88 165 (41%) 232 397 (15.6 in)
1999 0 4.85 b 249 0 249 (9.80 in)
(19.3 in) 0.5 6.23 a 198 (57%) 147 345 (13.6 in)
1.0 6.59 a 155 (34%) 294 449 (17.7 in)
2000 0 3.96 c -- -- --
(19.6 in) 0.5 6.81 b -- 153 -
1.0 8.14 a -- 298 -
2001 0 3.56 c -- -- --
(12.8 in) 0.5 6.06 b -- 165 -
1.0 7.31 a -- 320 -
ETc of Chardonnay grapevines as a function of irrigation
treatment and year. The separation of ETc into water
derived from the soil and that applied is also given.
260 mm = 841 l/vine (222 gal./vine) (vine x row = 5’ x 7’)

Question: How much is estimated vineyard
ET affected by year?
• Grapevine water use was estimated at one
location across several years.
• Water use was estimated for Chardonnay
grapevines on a 2.13 m (7 ft.) row spacing.
• The trellis was a VSP.

Seasonal Precipitation Estimated
Year Nov - Mar From 1 Apr DDs ETo ETc
---------- (mm) ---------- (> 10 C) ---------- (mm) ---------
1994 192 (7.6 in) 61 (2.4 in) 1408 1067 432 (17.0 in)
1995 843 (33.2 in) 47 (1.9 in) 1522 1032 447 (17.6 in)
1996 480 (18.9 in) 139 (5.5 in) 1548 1009 455 (17.9 in)
1997 522 (20.6 in) 38 (1.5 in) 1675 1066 503 (19.8 in)
1998 819 (32.2 in) 85 (3.3 in) 1369 885 346 (13.6 in)
1999 436 (17.2 in) 53 (2.1 in) 1357 988 378 (14.9 in)
2000 427 (16.8 in) 72 (2.8 in) 1446 975 410 (16.1 in)
2001 308 (12.1 in) 19 (0.7 in) 1519 1057 462 (18.2 in)
1481 1009 429 (16.9 in)
Seasonal precipitation, degree days (DDs) from 1 April
and reference ET (ETo) and estimated ETc (1 April to 1 Nov.)
of a Chardonnay vineyard in Carneros. VSP trellis w/vine x row
spacing of 5’ x 7’)
Available water to a depth of 2.75 m was estimated to be 275 mm (10.8 in) in this
vineyard (or 891 L/vine or 236 gal/vine).
ETc of 429 mm (16.9 in) is equivalent to 1390 L/vine or 368 gal/vine in this vineyard.

Question: How much is estimated vineyard
ET affected by year? Conclusions:
• The lowest value of estimated ETc (1997)
was only 69% that of the greatest (1998).
• ETo from 1998 was 83% that from 1997.
• The accumulation of DDs from 1997 were
81% that from 1997.
• The difference in ETc between the two
years were due to a combination of
differences in ETo and DDs. The
differences in DDs affected the Kc.

How can one get an estimate of
ETc in their vineyard?
Comparison of ETc determined with
a weighing lysimeter, Eddy
Covariance, Surface Renewal and
soil water budgeting.
C. Parry, T. Shapland, A. Calderon, L.
Williams and A. McElrone

SR is used to measure sensible heat flux,
and is then fed into the following energy
balance equation:
LE = RN – H – G
where LE is the latent heat flux density, RN is
the net radiation, G is the soil heat flux
density, and H is the sensible heat flux
density from SR.

Water use calculated with Surface Renewal
versus measured with a weighing lysimeter.

How much water is used
by vines as a function of
phenology throughout
the growing season?

Water use as a function of
phenology (% of total use).
Cultivar
BB 
Bloom
BB 
Veraison
BB 
Harvest Total
Thompson
Seedless 10 38 89
825 mm
(32.5 in)
Chardonnay
(Carneros) 10 38 78
429 mm
(16.9 in)
Merlot
(SJV) 10 52 82
716 mm
(28.2 in)
Red Cultivars
(SJV) 10 48 78
>828 mm
(32.6 in)

How to design irrigation strategies
for different soil profiles
(different soil textures and varying
depths):

When best to initiate irrigation
and whether it is better to
irrigate deeply and infrequently
or more frequently and
shallower

Deciding when to start irrigating
There are several methods: a.) measuring the
depletion of water in the soil profile to a pre-
determined value with a neutron probe (or other
such technique), b.) water budgeting, i.e.
calculating vineyard water use and subtracting
that from the amount of water in the profile (this
requires knowledge of the water holding
capacity of the soil and effective rooting depth)
and c.) using a plant based method such as
measuring leaf water potential. All three
methods could be used with low volume or
surface irrigation.

What information is needed to
determine when to start irrigating?
• An estimate of the amount of water available in
the soil profile (this can be determined with a
neutron probe, capacitance sensors,
tensiometers, etc.) or knowledge of soil type
• Rooting depth of the vines in your vineyard (a
good estimate is ~ 1.2 to 1.5 m (4 to 5 feet) but
water extraction may take place at greater
depths.
• An irrigation event would take place once a
pre-determined value of soil water was
depleted.

b.) Water budgeting
Estimates of vineyard water use and the
amount of water available in the soil profile
are needed when utilizing the water
budgeting method to determine when to
start irrigating the vineyard. Once the
irrigation season begins, this method can
be used to determine the intervals
between irrigations and the amount of
water to apply for flood or furrow irrigated
vines.

Example:
• Assume – a sandy loam soil in San Joaquin Valley
(Fresno area) with 1.2 m (4 ft.) rooting depth will contain
140 mm (1.38 in/foot) at field capacity while a clay loam
in Napa Valley (Oakville) will contain 190 mm (1.9
in/foot) at the same depth.
• Assume – trellis at both locations is a CA sprawl on an
11 foot row spacing and that the canopy developed
during the 2002 season.
• Allowable depletion is 50% (70 mm in the SJV and 85
mm in Napa Valley)
• Calculating ETc using 2002 reference ET data obtained
at each location the date of the first irrigation would
occur on May 19th near Fresno while that in Napa would
occur on June 19th.

Question:
Do vineyards on lighter soils require more
water once irrigations commence?
Answer:
ET of the vineyard is driven by evaporative
demand and canopy development. Assuming
that soil water is not limiting, ET of two vineyards
on different soil types will be the same as would
their irrigation requirements. If the water applied
to the lighter soil is lost below the rootzone, then
irrigation requirements will be greater. One
means to overcome this is to schedule irrigations
at a higher frequency with lowered amounts.

How to best monitor plant water
status and soil moisture:

Plant based techniques I’ve used:
• Pre-dawn leaf, midday stem and midday
leaf water potentials.
• Stomatal conductance and photosynthesis.
• Correlated above with soil water content
and soil matric potential
• Canopy temperature
• Crop Water Stress Index (CWSI)
• Remote sensing (UAV) to calculate CWSI
other stress indices

Plant based measurements of
water status should reflect the
amount of water available in the
soil profile (Higgs and Jones,
1990; Jones 1990).

Relationships among predawn (ΨPD), midday leaf
(Ψl), and midday stem (Ψstem) water potentials and
mean soil matric potential (Ψπ) of a Hanford fine
sandy loam.
• ΨPD = -0.059 + 0.94x
(R2 = 0.56 ***)
• Midday Ψl = -0.476 + 5.72x
(R2 = 0.88 ***)
• Midday Ψstem = -0.126 + 6.85x
(R2 = 0.83 ***)
• X in the above equations is soil matric potential

In general, most of the plant based techniques I’ve
used are highly correlated with one another and with
soil water content. I would use the one that is most
convenient and that a person feels most comfortable
with. I am of the opinion that any of methods (plant or
soil based) discussed could be used to determine
when to initiate irrigation early in the season. Once
the decision to irrigate has been made I would
calculate ETc using the product of ETo and Kc. I would
then irrigate at some fraction of ETc using sustained
deficit irrigation (SDI) or regulated deficit irrigation
(RDI). The fraction of ETc used to determine applied
water amounts would be based upon previous
experience in a particular vineyard and production
goals.

How do temperature spikes affect
vineyard ET and how best to mitigate
them?
The next slide contains data from
Napa Valley in 2002 during which I
was collecting data. It shows the
effect of rapid increases in maximum
ambient temperature on the
calculation of reference ET (ETo).
Remember: ETc = ETo x Kc

Data from CIMIS station at
the Oakville research station
ETc = ETo x Kc
Reference ET was more
highly correlated with SR
during July than with max.
daily temperature.
75 F
105 F

Conclusions:
• Mean maximum daily temperature for the month
was 29.2o
C (~85o
F). That recorded on July 9th
was 40.5o
C (~105o
F). Others in Napa Valley
recorded 113o
F.
• Reference ET was ~ 30% greater on July 9th
compared to the mean monthly ETo.
• Would grapevine ETc also increase? It has been
shown in Australia that high temperatures
upregulate stomatal conductance of grapevines.
• Vapor pressure deficit (VPD) also increased
greatly during the heat spell.
• VPD has also been shown to decrease stomatal
conductance in a linear fashion.

How do temperature spikes
affect vineyard ET and how best
to mitigate them?
What else may be affected by
these temperature spikes?

Cabernet Sauvignon near Oakville: July 18th 2002

Desiccated berries of Cabernet Sauvignon grown in Lake County.

An attempt was made to quantify the
sunburn damage across most of the
treatments (trellis, rootstock, irrigation
amount and spacing)
• Only the 0.0 and 0.75 of estimated ETc
irrigation treatments were examined.
• The total number of clusters per a four vine
plot were counted. The four vine plots were
replicated four times.
• A cluster was considered sunburned if it had
a minimum of 5 sunburned berries.
• A cluster was considered desiccated if ~ 50%
of the berries were dried.
• Data were collected on July 18, 2002.

1 x 1 m VSP Cabernet Sauvignon vineyard in Napa Valley.
Row direction was approximately east/west.

Row direction was approximately east/west.

Trellis and/or Irrigation % of total clusters
Row Spacing Rootstock Treatment w/sunburn desiccated
VSP 1 x 1 m 5C 0.0 97 70
0.75 94 46
110R 0.0 77 19
0.75 77 17
VSP 9 ft. row 5C 0.0 28 --
0.75 17 --
110R 0.0 8 --
0.75 7 --
Lyre 9 ft. row 5C 0.0 86 --
0.75 66 --
110R 0.0 43 --
0.75 19 --
The effect of trellis and/or row spacing, rootstock and applied
water amounts on the percentage of Cabernet Sauvignon clusters
w/sunburn. Row direction ~ east/west. LSD0.05 for w/sunburn
column = 12

Average effects of treatments
on clusters with sunburn
• Trellis/training: VSP 1x1 m = 87; VSP 9 ft.
= 15; Lyre 9 ft. = 54
• Rootstock: 5C = 65; 110R = 38
• Irrigation: 0.0 = 57; 0.75 = 47
• There was a significant effect of rootstock
(LSD0.05 = 17) and irrigation amount
(LSD0.05 = 17) on desiccated clusters in
the 1x1 meter spacing.

Sunburn of grape berries:
• For grape berries to sunburn I am of the
opinion several factors are necessary.
• Very high ambient or berry temperatures
(> 40C [104F])
• Direct, prolonged exposure (> 2 - 3 hr.) to
solar radiation
• Intermittent exposure of an individual berry
to direct solar radiation will mitigate the
degree of sunburn (California sprawl
canopy will provide such protection)

Minimize sunburn/desiccation
• Provide good canopy coverage of the
fruit.
• While light can be beneficial to
enhancing fruit composition, minimize
fruit exposure during the hottest
portion of the day.
• Row direction and trellis type in
minimizing fruit exposure should be
considered

How to deal with the
possibility of losing
your water supply
before harvest.

Effects of cultivar and irrigation treatments
on yield of vines grown in the San
Joaquin Valley.
• Seventeen red, wine cultivars grown at the
KARE Center.
• All grafted onto 1103P.
• Irrigation treatments consisted of 1.) full
ETc from 1st irrigation to veraison and then
no applied water, 2.) applied water at 50%
of ETc season long and 3.) no applied
water to veraison and then applied water
at 50% of ETc up to harvest.

Cultivar
Aglianico
Cabernet Sauvignon
Cinsault
Durif
Freisa
Grenache noir
Malbec
Montepulciano
Petit Verdot
Refosco
Sauzao
Syrah
Tannat
Tempranillo
Tinta Amarella
Tinta Madeira
Touriga Nacional
Red wine grape cultivars used in the study.

Applied water amounts as a % of full ET for the irrigation treatments across
years. (5.58 m2/vine = 1792 vine/ha = 725 vines/acre). A mean of 833 mm
of water is equivalent to 1230 gallons/vine. I  Ni: full ET from 1st irrigation
of season to veraison, then no applied water. NI  0.5: no applied water to
veraison, then 50% ETc. 0.5 ETc: 50% season long.
---------------- Irrigation Treatment -----------------
Year I  Ni 0.5 ETc NI  0.5 100% ETc Rainfall
(applied water amounts % full ET) (mm)(in.) (in.)
2012 49% 59% 39% 780 (30.7) 2.4/4.3
2013 54% 53% 29% 821 (32.3) 4.3/0.8
2014 62% 52% 28% 846 (33.3) 2.2/2.2
2015 42% 51% 36% 829 (32.6) 2.1/1.1
mean 52% 54% 33% 833 (32.7)
2016* 100% 54% 100% 891 (35.1) 9.3/2.0
*Treatments were irrigated at 100% ETc except for the 0.5 ETc treatment.

The effect of irrigation treatment on berry weight at
harvest across years. Values are the means of 17, red
wine grape cultivars grown at the Kearney Agricultural
Research and Extension Center.
----------------- Irrigation Treatment -----------------
Year I  Ni 0.5 ETc NI  0.5 1.0 ETc
------------------- weight (g berry-1) ------------------
2012 1.44 (76%)* 1.52 (80%) 1.08 (57%) 1.89
2013 1.63 1.58 1.23 ---
2014 1.61 1.52 1.02 ---
2015 1.30 (72%) 1.59 (88%) 1.26 (70%) 1.81
mean 1.50 1.55 1.15 1.85
2016** 1.81 b 1.76 b 1.92 a
*Percent of 1.0 ETc treatment
** all treatments were irrigated at full ETc except the 0.5 ETc treatment.

The effect of irrigation treatment on soluble solids across years.
Values are the means of 17, red wine grape cultivars planted at
the Kearney Agricultural Research and Extension Center.
-------------------- Soluble solids (Brix) -------------------
2012* 24.6 24.0 22.3 23.8
2013 24.5 24.1 24.0 ---
2014 24.6 23.8 22.9 ---
2015* 28.2 26.1 24.7 24.6
2016** 22.3 22.7 22.3 ---
*all treatments harvested on the same day
** all treatments were irrigated at full ET except the 0.5 ETc treatment.

The effect of irrigation treatment on yield across years. Values
are the means of 17, red wine grape cultivars planted at the
Kearney Agricultural Research and Extension Center. (5.58
m2/vine = 1792 vine/ha = 725 vines/acre).
---------------------- Yield (kg vine-1) ---------------------
2012 11.7 11.9 7.2 14.3
2013 13.3 12.3 8.1 ---
2014 9.6 10.4 5.4 ---
2015 7.4 9.0 5.6 10.9
2016* 10.8 a 10.1 ab 9.9 b 12.2
t/acre** 33.2 34.7 21.0 ---
*Treatments were irrigated at 100% ETc except for the 0.5 ETc treatment.
**Total yield across the first four years of the study as a function of irrigation treatment.

The effect of irrigation treatment on number of clusters per vine
across years. Values are the means of 17, red wine grape cultivars
planted at the Kearney Agricultural Research and Extension Center.
Treatments first applied in 2012.
----- Irrigation Treatment ------
Year I  Ni 0.5 ETc NI  0.5
------------ Cluster #/vine ------------
2013 57 + 7 54 + 7 48 + 8
2014 49 + 8 45 + 7 38 + 5
2015 44 + 7 44 + 8 35 + 5
2016* 45.0 a 43.0 ab 40.6 b
I  Ni = 100 ETc between berry set and veraison, no water after veraison
Ni  I = no water between berry set and veraison, 50% ETc after veraison
0.5 ETc = applied water at 50% of ETc all season.
* all treatments were irrigated at 100% of ETc season long except the 0.5 ETc.

Conclusions
• Early season stress (NI  I) significantly reduced
berry size and yield across cultivars compared to
the 0.5 ETc and late season (I  ni) stress
treatments. Early season stress also delayed the
accumulation of sugar.
• Cluster number per vine was reduced in the NI  I
irrigation treatment compared to the other two trts.
• The I  ni treatment had the greatest TA values in
2013 and highest total wine anthocyanins in 2014
compared to the two other treatments.
• The data would indicate that there are irrigation
strategies to minimize reduction in yields of wine
grapes due to limited water availability and
possibly maximize fruit (wine) composition.

Potential vineyard
evapotranspiration (ET) due to
global warming: Comparison of
vineyard ET at three locations in
California differing in mean
seasonal temperatures

Background
• An increase in global temperature has been
predicted to increase evaporative demand
as it is controlled by temperature, net
radiation, wind and relative humidity.
• Rainfall timing and amount may also
change to due an increase in temperature.
• An increase in temperature will accelerate
vegetative growth (canopy development).
• Such changes may result in an increased
demand for vineyard irrigation to minimize
yield reductions due to water stress.

Methods
• Reference ET, temperature and degree-
day data were obtained (using 2009 data)
from three locations in California: the
Carneros district at the southern end of
Napa Valley, Lodi located in the northern
San Joaquin Valley and Parlier (Fresno)
located in the southern San Joaquin Valley.
• Carneros: 38o 13’ N/122o 21’ W (2 m elev.)
• Lodi: 38o 8’ N/121o 23’ W (8 m elev.)
• Parlier: 36o 36’ N/119o 21’ W (103 m elev.)

Lodi
Parlier
Carneros
Map of California
North
Pacific
Ocean

Methods
• It was assumed that the same cultivar and
rootstock was used at all locations.
• It was assumed that the trellis/canopy type
was a California sprawl and that the
vineyards had row spacings of 3.35 m (11 ft.).
• The seasonal Kc was a function of degree
days (> 10 C) using temperature data
recorded at CIMIS weather stations from
each location (obtained from the UC IPM website and
calculated using the single sine method). The seasonal
maximum Kc was 0.82 at all locations.

Typical California sprawl type canopy
3.05 m (10 ft.) between rows in this vineyard

Monthly mean high temperature at three
locations in California during the 2009
growing season
--------------- Temperature (oC) --------------
Month Parlier Lodi Carneros
March 19.8 18.5 18.1
April 23.6 22.6 20.6
May 30.7 27.7 22.8
June 30.7 28.2 24.8
July 36.9 31.3 26.5
August 34.8 31.4 27.8
September 33.5 31.7 28.9
October 23.5 22.9 22.5
Mean 29.2 26.8 24.0

Cumulative DDs from March 15 to October 31. Cumulative DDs at
Carneros and Lodi are 59 and 80%, respectively, those at Parlier
(To convert from degree days in C to F, multiply by 1.8.)
2835 (II)
3864 (IV)
4806 (V)
DDs
Base 50 F

Cumulative ETo from March 15 to October 31. ETo values at
Carneros and Lodi are 84 and 95% that at Parlier.
44.7 in.
42.5 in.
37.6 in.

Cumulative estimated vineyard ET from March 15 to October 31.
ETc values at Carneros and Lodi are 77 and 94%, respectively,
that at Parlier.

Conclusions
• Mean monthly temperature at Parlier was 5.4
and 2.4 C greater than those at Carneros and
Lodi, respectively across the growing season.
• However, mean monthly solar radiation at
Parlier was only 10 and < 1% greater than
those at Carneros and Lodi, respectively.
• Thus the differences in ETo across locations
were less than one may assume based solely
upon temperature data. Seasonal ETo at
Carneros and Lodi were 84 and 95% that at
Parlier, respectively.

Conclusions
• Estimated vineyard ET at Parlier was 39 and 6% greater
than those at Carneros and Lodi, respectively.
• The greater ET at Parlier compared to the other locations
was due in part to a more rapid canopy development in
response to increased temperature (affecting the seasonal
crop coefficient).
• Based upon the data presented in this talk, an increase in
seasonal temperature in a viticultural region more than
likely will increase vineyard water demand.
• This does not take into account a continued increase in
CO2 concentration and/or decreases in VPD. Such an
increase may decrease vineyard water use due to a
reduction in stomatal conductance which may mitigate
increases in evaporative demand as demonstrated by
recent research.

Conclusions
• Estimated vineyard irrigation requirements due to
global warming will depend upon several other
factors to include: rooting depth and soil type and
viticultural practices such as row spacing, trellis
used and grape type (raisin, table or wine grapes).
• The seasonal pattern of rainfall and its amount will
also affect irrigation requirements.
• The absolute difference in grape growing regions
presented here did not take into account date of
harvest. If harvest date in delayed in the cooler
growing region then ETc from budbreak to harvest
(and not until the end of October) may be more
similar across regions than presented here.

Things you can do to assist in
irrigation management.
• Get an estimate of ET for your vineyard(s).
• Collect degree days from budbreak each year and
determine DDs as a function of phenological
events.
• Download ETo data from closest CIMIS station (or
other means).
• Download rainfall amounts/events.
• Measure applied water amounts and record as a
function of time (DDs).
• Using the above develop an irrigation coefficient.

2017 Oregon Wine Symposium | Dr. Larry Williams- Coping Strategies for a Warmer Climate: Irrigation and Canopy Management

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2017 Oregon Wine Symposium | Dr. Larry Williams- Coping Strategies for a Warmer Climate: Irrigation and Canopy Management