PCC June July 2021 e

loss and maturation delay.
Currently, there are different ways
growers can adjust irrigation based
on weather condition: 1) National
Weather Service (digital.weather.gov/)
provides the weather forecast as well
as forecasted ETo. Growers can adjust
the irrigation amount based on
forecasted weather and ET. 2) UCCE
is launching weekly crop ET reports
(ucanr.edu/sites/viticulture-fresno/
Irrigation_Scheduling/), so growers do
not need to calculate weekly grapevine
ET or gallons/vine/week themselves.
Irrigation can be simply followed on
the ET reports.
Figure 2: Crop coefficient (Kc) is correlated with canopy size measured by leaf area.
Figure is elaborated in Williams and Trout 2005.
Finally, growers need to put economic
consideration into water management.
Water might be better used for younger
blocks than a vineyard which is
near the end of its lifespan, and it also
makes more economic sense to use
water for the cultivar which has a better
price when the water is scarce. The
take-home message on vineyard water
management is:
98
0.4
• Check soil moisture at all levels.
Maximum daily air temperature (F
96
94
92
90
88
86
84
82
80
78
Max daily temperature (r 2 =0.81)
Daily ETo (r 2 =0.97)
76
0.0
300 350 400 450 500 550 600 650 700
0.3
0.2
0.1
Daily ETo (in)
• Assess canopy, vine water status and
weather condition.
• Spend water when it is needed the
most.
• Salinity becomes an important
factor in determining water
management.
• Mow cover crop or middle row
vegetation early to preserve soil
moisture.
Solar radiation (Ly/day)
Figure 3: Sunlight is strongly correlated with ETo and ambient temperature. Data points are
extracted from last 10 years’ average during months of August, September and October at CIMIS
station #56 in Los Banos.
Continued from Page 37
condition (Figure 3). ETo is strongly
correlated with sunlight and the ambient
temperature. A sunny and cloudless
day will drive more grapevine water
use than a cloudy and foggy day or a
smokey day as occurred last year due
to the wildfires. Similarly, a forecasted
heat wave will cause severe water stress
if there is lack of irrigation. Water
stress coupled with temperatures >100
degrees F disrupts berry growth and
sugar accumulation and causes yield
References
Williams, L. and Trout, T. 2005. Relationships
among Vine- and Soil-Based Measures of Water
Status in a Thompson Seedless Vineyard in Response
to High-Frequency Drip Irrigation. Am J
Enol Vitic. 56: 357-366.
L. P. Christensen. 2000. Raisin Production Manual.
University of California Agriculture and Natural
Resources Publication 3393.
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38 Progressive Crop Consultant July / August 2021