VOL. 16/NO. 2
Summer 2015
Saving
Water
and Money:
Irrigation for Increased Nursery
Profitability and Efficiency
UT Gardens’ 2014 Best
& Beautiful Edibles,
Shrubs, Trees and Roses
Pick Your Pot...
Are Container Alternatives
Right for Your Nursery Operation?
VOL. 16/NO. 2 •
Cover Story
Saving Water and Money:
Irrigating for Increased
Profitability and Efficiency
10
In the landscape
UT Gardens’ 2014
Best & Beautiful Edibles,
Shrubs, Trees and Roses
14
Summer 2015
In the nursery
Pick Your Pot...
Are Container Alternatives
Right for Your Operation?
18
more features
Green Gatherings
Tennessee Green Industry Expo,
September 17–18, 2015, Nashville, TN..........................................................................7
DEPARTMENTS
From the President, Jeff Harrell.....................................................................................6
Recent Event....................................................................................................................8
TNLA New Members.......................................................................................................9
Index of Advertisers.......................................................................................................21
Calendar of Events.........................................................................................................22
4
tennessee greentimes SUMMER 2015
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Cover Story
Saving
WATER, Saving
MONEY:
Irrigating for Increased Nursery
Profitability and Efficiency
By Halee Jones, Recent Graduate, Department of Plant Sciences, and Amy Fulcher, Ph.D.,
Extension Specialist and Assistant Professor for Sustainable Ornamental Plant Production
and Landscape Management, The University of Tennessee
In
the first article in this series,
“Nursery Irrigation: The
Importance of Water
Availability and Efficiency,” published
in the Spring 2015 issue of Tennessee
GreenTimes, we discussed reasons why
nursery growers may want to look closely
at their water use, including issues that
could lead to water scarcity and the economic and production benefits to refining
water use. In this article, second in the
series of three, we will cover how growers
can make small or big changes to their
irrigation practices that improve not
only plant quality and profitability, but
also reduce water consumption.
Growers who use water effectively
not only help reduce the demand for
freshwater resources, but they also cut
costs and increase production efficiency
in their nursery. While water is critical
to plants, both too much and too little
can be harmful. Plants that don’t receive
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tennessee greentimes SUMMER 2015
the needed amount of irrigation grow
more slowly, which increases the amount
of time it takes to reach a mature or marketable plant size. Conversely, too much
water can also slow growth and lead to
root rot, increased fungicide use (and
related costs) and increased plant death.
When the distribution within a zone
is not even, growers will use more water
to irrigate. For example, when water
distribution (measured as distribution
uniformity) is not consistent, an overhead irrigation system will often be
operated to sufficiently wet the driest
areas, meaning that plants in other
areas of the zone are over irrigated.
Let’s examine some ways that growers
can increase the uniformity and
efficiency of irrigation.
Identifying inefficiencies
The most common form of irrigation in
the nursery industry is overhead irriga-
tion. Overhead irrigation is the cheapest
and most effective method of irrigating
relatively small container sizes. Overhead irrigation systems are useful
when covering large areas of land. They
also don’t require the messy and more
expensive tubing that drip irrigation
systems require.
However, overhead irrigation is also
the most wasteful form of irrigation.
Inefficiency can easily occur with overhead irrigation due to poor distribution
uniformity (as mentioned above), which
can be caused by inappropriate system
design or clogged, worn and/or damaged
emitters or risers (see Photo 1). In addition, overhead irrigation of container
crops is inherently wasteful due to poor
application efficiency, specifically poor
interception efficiency. Depending on
pot spacing, up to 80% of overhead
irrigation misses the intended target. By
spacing pots closer together, we reduce
the amount of space between containers
and usually increase the amount of water
intercepted by containers, which
increases efficiency (Photo 2).
Weather also plays a role in application efficiency. Wind speed and sun
intensity increase as the day progresses.
Greater wind and air temperature
reduce overhead irrigation application
efficiency due to drift and evaporation,
and they increase the need for irrigation.
This is why natural or constructed
windbreaks should be used to minimize
wind and improve irrigation application
efficiency and uniformity. Wind, evaporation, inappropriate plant spacing, poor
system design and clogged emitters will
lead to over or under irrigation of part
or all of the target crops.
The potential consequences of inefficient irrigation include wasted water,
increased nutrient and pesticide leaching
(removing nutrients and pesticides from
the foliage and container substrate),
increased water runoff and movement of
contaminants in runoff from production
surfaces, increased insect, mite and disease problems and water stress, reduced
plant growth, increased plant death and
increased production duration.
Irrigation and IPM
Many nursery growers now use
Integrated Pest Management
(IPM) strategies to produce their
crops. Not only does IPM help control pests, but also it can reduce
pesticides in runoff. In fact, a study
conducted at Clemson University
shows that the implementation of
IPM strategies effectively reduces
the amount of fungicides transported in runoff water, without
compromising container plant
health or marketability. Combining IPM along with refined
irrigation practices can lead
to many benefits, both for the
producer and the environment.
How can you tell if plants
have similar water needs?
Section Name
Photo 1. Risers that are not 90 degrees
can lead to poor irrigation uniformity.
Nutrient and pesticide leaching can
create a number of problems. The need
to reapply controlled-release fertilizers
and preemergent herbicides and other
pesticides more frequently or to use
higher rates will have a negative impact
on nursery profits. Nutrient or pesticidecontaminated leachate can also cause
harm to the environment.
Luckily, many practices — some of
them easy and inexpensive — can be integrated into nursery production to improve
irrigation efficiency and avoid the problems associated with inefficient irrigation.
Improving irrigation efficiency
Photo 2. When they are small, plants can
be spaced pot-to-pot (like the boxwoods in
the foreground) to increase the interception
of irrigation water. Carefully space the
plants as they grow so that excess spacing
doesn’t cause inefficient irrigation.
Cyclic Irrigation
6 am
11 am
3 pm
Standard Timer-Based Irrigation
6 am
Figure 1. In cyclic irrigation (top), the
volume of applied water needed per day
is divided among three smaller irrigation
events, as opposed to standard timerbased irrigation (bottom) that typically
comes on in the early morning and is left
on for a long time.
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tennessee greentimes SUMMER 2015
Some simple practices that improve
efficiency include choosing a substrate
with adequate or enhanced water-holding
capacity, grouping plants into zones
based on water requirements, spacing
plants within a zone and refining irrigation timing and volume (collectively
known as irrigation scheduling), along
with irrigation system design and
delivery. However, until the distribution
uniformity is at an appropriate level, the
benefits of these efforts will not be maximized. As mentioned above, distribution
uniformity is the measure of an irrigation
system’s ability to apply water evenly
within a zone, which in turn will affect
how much water is being applied. Measuring distribution uniformity will be described in detail in our third article (to be
published in the Fall 2015 issue of Tennessee GreenTimes). Along with checking, and if needed, improving your
distribution uniformity, consider adopting
some of the low-tech and/or high-tech
ways to improve irrigation efficiency that
are discussed in the following paragraphs.
Grouping plants into zones based on
water requirements can lead to more efficient water use. See the sidebar (above,
right) for information on how to determine water requirements for different
species. Decreasing the space between
each plant will decrease the amount of
water that falls between containers, hits
the ground and becomes runoff.
However, consider the role that canopy
shape and size play on intercepting
overhead irrigation and rainfall. The
smaller a plant is (for example, early
in the production cycle), the less of a
With a bathroom scale, you can
use this simple technique!
1. Water plants.
2. Weigh after plants stop dripping.
3. Weigh again 24 hours later.
4. The difference is water used by
the plant (and evaporated from
the substrate) in one day.
5. Compare different species’
water use to decide how to
group plants in irrigation zones.
factor the canopy is, and close spacing
can be used to increase interception
efficiency. The larger a plant becomes,
the more canopy size and shape play a
role in funneling water down into the
container or, conversely, shedding water
away from the container. When water
is channeled by the canopy toward the
container, space plants adequately so that
they are sure not to “rob” one another of
water. Also, adjust irrigation time accordingly, as more water than the application
rate would indicate is going into the
container. Knowing your application
rate is an important step in refining
nursery irrigation efficiency and will
be described in our Fall 2015 article.
Adjusting irrigation timing is a simple
and cheap way to increase irrigation efficiency. Irrigating in the early morning
hours can decrease losses to evaporation
and drift, but will negate some of the
plant growth benefits of irrigating in
hotter parts of the day. By using cyclic
irrigation — dividing the same irrigation
volume into three separate events
throughout the day — water has time to
soak in (see Figure 1). Cyclic irrigation
can decrease water use by 25% and prevent runoff, as well as increase growth.
Refining irrigation volume is another
easy way to irrigate efficiently. One
method to refine the irrigation volume is
by calculating the leaching fraction. The
leaching fraction is the amount of water
applied during an irrigation cycle that
drains out of the container compared to
the amount that is applied (easily defined
as excess water). A leaching fraction
of 10% to 20% allows for water and
nutrient conservation. Our Fall 2015 article will describe how to determine LF.
Basing irrigation on the soil or
container-substrate moisture level is
another way to refine irrigation. Water
in soil and container substrates is divided
between plant-available water and
unavailable water. A tensiometer is a
probe-like device that can be used to
determine the amount of water available
to plants growing in field soil, which
is very valuable, but generally does not
perform well in container substrates,
which are coarse in comparison to soil.
Capacitance sensors determine volumetric
water content, and while very useful,
they do not account for the amount of
water actually available to the plant.
However, even without probes it is
easy to determine irrigation volume
needed by weight. Start by watering a
plant thoroughly, let it drain to container
capacity (when it stops dripping, usually
after 30 minutes to 1 hour, depending
on container size), and then weigh it.
Reweigh it 24 hours later. The difference in weight is used to determine
the water lost in one day. This water loss
is a combination of evaporation from the
substrate and the transpiration from the
plant, what is collectively referred to as
evapotranspiration. By knowing the
system’s application rate and that 1 gram
of water equals one milliliter of water
(varies slightly by temperature), a grower
can adjust the irrigation duration to precisely apply the amount of water lost in
the previous 24 hours. A similar type of
daily water-use system can be automated
by using capacitance sensors to sense the
change in water content each day and trigger irrigation solenoid valves to replace
the amount lost in the previous 24 hours.
Summary
Increasing irrigation efficiency can
lead to many benefits, including shorter
production cycles, decreased root rot
and use of fungicides, and increased
intervals between preemergence herbicide applications. The concepts described
above range from very simple to using
automated moisture-sensor-based
irrigation systems. Consider trying one
new technique this summer, and see
what benefits you experience! C
This article was sponsored by the
Southern Risk Management Education
Center, USDA NIFA and The University
of Tennessee Institute of Agriculture.