The Crush - June 2019 - 2

[ FEATURE STORY ]
"Growers trust what they see with their eyes on the vine,"
Shapland said. "A monitoring system's data has to support what
the grower sees on the ground."
SOIL MOISTURE MONITORING
Mark Greenspan, viticulturist and consultant with Advanced
Viticulture, has used soil moisture sensors to schedule irrigation
for vineyard clients since 2010. Types of sensors available include
moisture block sensors and individual capacitance sensors.
Greenspan uses sealed tube probe sensors that measure soil
moisture at specific depth intervals to provide continuous data
at individual levels, as well as a provide a soil moisture profile.
"Soil moisture depth charts can be very informative during the
spring dry-down phase to determine when to start irrigation," he
said. In addition, soil sensors provide information to determine
the depth of irrigation, the time required for profile wetting, and
the timing of precise irrigations to maintain the desired soil water
profile. Greenspan said, "Don't neglect what's happening below
ground. It's half of our system."
SAP FLOW MONITORING
Thibaut Scholasch of Fruition Sciences supplies sap flow sensors,
a continuous, non-destructive technology attached to a vine
trunk that measures sap temperatures to quantify stress relative
to potential vine transpiration. Scholasch acknowledged that
every method of water stress measurement has limitations, and it
is often better to use more than one method. Under best practices
for water stress management, he advised: 1. Distinguish water
stress from water use. 2. Water stress - not water use - impacts
fruit composition and yield.
He suggested delaying the first irrigation of the season as much
as possible, provided canopy development is sufficient. He
said, "Early season water deficit toughens up the vine hydraulic
system." Based on experience he advised: Favor large/less
frequent irrigations that result in less accumulated stress over the
season; more irrigation induces faster ET and faster soil moisture
depletion; and avoid the "junkie effect" (the more water you
apply, the more the plant will need).
OTHER VITICULTURISTS' PERSPECTIVES
Daniel Bosch, viticulturist for Constellation Brands California
vineyards, advised paying attention to the basics of irrigation
management. This includes evaluating irrigation system
uniformity and system capacity in terms of application volume/
minute, pumps, wells, reservoirs and filters.
Create a plan for the year that takes into account yield goals, soil
moisture at the beginning of the season, salt issues, fertigation
needs, canopy growth and fruit exposure, when vine growth
should stop, and wine quality and style. He uses flow meters
to know if the correct water amount is applied, soil moisture
sensors to check irrigation depth to avoid wasting water below
2 / JUNE 2019

Vineyard irrigation can be better managed with sensor and monitoring technologies.
Photo: Ted Rieger

the root zone, and he measures leaf water potential. He also
uses the vineyard soil irrigation model (VSIM) that uses aerial
imagery to assist with irrigation scheduling.
"Erroneous seasonal data can lead to disastrous outcomes.
Redundancy of measurements is needed," said Mark Battany, UC
Cooperative Extension Central Coast viticulture advisor.
WILLIAMS REVIEWS WATER STATUS TOOLS
The UCD seminar also honored the work of Professor Emeritus
Dr. Larry Williams, who spent his career as a plant physiologist
studying grapevine water status and evaluating measurement
tools while based at the Kearney Agricultural Research and
Extension Center in Fresno County. The seminar provided a
paper by Williams that appeared in 2017 from the Proceedings
of the IX International Symposium on Grapevine Physiology
and Biotechnology by the International Society for Horticultural
Science: "Physiological tools to assess vine water status for use in
vineyard irrigation management: review and update."
In the paper, Williams reviewed the following physiological
methods to assess vine water status and estimate vineyard
water use: leaf and stem water potentials, stomatal conductance,
thermal imaging and crop water stress index, estimating water
use with ET and crop coefficients, soil water content, and sap
flow sensors. Based on his review, he wrote this conclusion:
"In general, most of the physiological methods outlined in this
paper 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
methods (plant or soil based) discussed herein could be used to
determine when to initiate irrigation early in the season. Once
the decision to irrigate has been made, I would calculate crop
ET (ETc) using the product of reference ET (ETo) and the crop
coefficient (Kc). I would then irrigate at some fraction of ETc
using sustained deficit irrigation or regulated deficit irrigation.
The fraction of ETc used to determine applied water amounts
would be based upon previous experience in a particular
vineyard and production goals."



The Crush - June 2019

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