February 2022 - 42

PRODUCTION
MAXIMIZING
Irrigation Efficiency
Here are some of the key considerations to optimizing the efficiency of an irrigation system.
BY AL ZYLSTRA
I
haven't kept track, but I estimate that I've
walked through more than a thousand
growing facilities ... greenhouses, nurseries,
indoor vertical farms and field operations ...
over the past 35 years. I have been designing,
supplying and supporting the environment
systems - irrigation, water management and
treatment, control and heating systems - for
them for more than 30 years.
It has been a privilege to work with some of the
best and most innovative growers on the planet
and observe many of them contribute to the
development of the best technologies available
today, such as the development of flood floors;
pressure compensated drip emitters; traveling
irrigation booms; computerized irrigation;
nutrient management systems; and more. My
travels have allowed me to observe the best
technologies and practices available, but also
some of the crudest and least efficient ways of
getting things done imaginable. In this article, I
will address some of my observations regarding
irrigation efficiency.
There are no alarming revelations here, just
a summary of some key tools and factors to
optimize the efficiency of an irrigation system.
There is one observation however that may be
a bit startling. I have observed, and read about,
some growing facilities that waste as much as
50% (some I suspect even more) of their total
irrigation water drawn from the source. That
may include unnecessary use of reverse osmosis
resulting in immediately dumping 25-40% of
the incoming source water, failing to fix leaks,
irrigation zones and delivery systems that do
not match the crop, lack of control of irrigation
decisions and timing, just plain old overwatering,
overspray, and more.
Of course, there is also the matter of increasing
pressure on water use efficiency brought on
by droughts; water resource re-allocation due
42 FEBRUARY 2022 GPNMAG.COM
to climate change concerns; water pollution
from irrigation runoff; loss of use of resources
for wildlife preservation; and, in some areas,
salt intrusion resulting from reduced aquifer
levels. Lots of good reasons to make sure your
irrigation systems are designed and operating at
optimum efficiency.
START AT THE PLANT
Someone in the industry coined the term
" plantcentric design " several years ago, which
simply refers to designing systems with the needs
of the plants being grown at the forefront. Sort
of a version of form follows function engineering.
Plantcentric design is more important than
ever as average facility size and corresponding
management challenges both get bigger. All
irrigation system design should start at the
plant, or crop level. What is the water budget for
that crop, whether that is measured in milliliters
or liters per plant per day, or liters per square
foot, or gallons per acre per day? For monocrop
facilities or monocrop zones, that means
identifying the water required per plant/day
for each stage of growth that will be grown in
that zone. For example, a potted plant crop at
1.5 square foot per plant density in a 30 x 96 foot
climate zone may demand 1.5 liters per plant per
day for 1,920 plants, resulting in a total irrigation
budget of 2,880 liters or 762 gallons per day
(gpd) for that area.
Alternatively, a bedding plant grower may
grow multiple types of crops in a year in the
same zone. If that crop varies greatly in size,
say propagation in early spring and poinsettias
in the fall, this requires identifying both the
minimum and maximum water demands in that
zone and making sure the system is designed to
provide efficient irrigation for both extremes. That
result then is expressed in liters or milliliters per
square foot of crop area instead of per plant. The
minimum irrigation demand may be
0.5 liter/0.13 gallons to a maximum of as much
as 1.5 liters/0.40 gallons per square foot per day.
GRANULAR IRRIGATION ZONING
Once a water budget is determined for a
particular area, it may be beneficial to divide that
area into multiple smaller irrigation zones to allow
maximum efficiency in irrigation control. This
avoids irrigating two or more types of crops with
different water demands, or worse yet a bare floor
or bench, with the same amount of water and the
same irrigation cycle frequency. Making a higher
quantity of smaller irrigation zones reduces
overwatering of one crop and/or underwatering
of the other. Adding zones means more solenoid
valves and PVC but that granularity pays off over
time by increasing overall irrigation efficiency and
improved plant quality.
Granular irrigation zoning has multiple irrigation
zone valves, each serving a small area for improved
controllability.

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February 2022

Table of Contents for the Digital Edition of February 2022