March 2019 - 15

WATER MANAGEMENT
Figure 2a. The Meter Group makes this moisture sensor, the 5TM. It monitors
soil moisture and temperature. This sensor is approximately 2 inches long, so
it will fit in a 4-inch pot.
IMPLEMENTING EFFICIENT
IRRIGATION AT YOUR GREENHOUSE
The majority of sensors currently
available measure the amount of water
in the soil based on volume (Figure 2).
The soil moisture is a ratio of the volume
of moisture to the volume of substrate,
which is often expressed as a percent. In
most media, we have found that irrigating
at a moisture content between 25 and 45
percent will provide good quality growth
(Figure 1). As discussed above, irrigating
at a lower moisture content will reduce
shoot elongation without the use of
chemical growth retardants.
One of the greatest challenges currently
is deciding how to use soil moisture
sensors in your greenhouse. Some growers
use sensors exclusively for monitoring
their current irrigation practices. However,
other growers are interested in automating
their irrigation based on measurements
from sensors. These options are all
possible, but automating irrigation
based on measurements from sensors
is probably the most challenging way to
implement sensors into your greenhouse.
If you are interested in monitoring
irrigation, you can purchase loggers with
most sensors that can be used to provide
you with more detailed information about
your soil moisture. Many environmental
control systems will measure soil moisture
along with other environmental variables.
Figure 2b. The 10HS sensor is also made by the Meter Group. It only measures
soil moisture, but it is larger than the 5TM sensor (approximately 4 to 5 inches
long). It may be a good choice for perennial production in larger containers.
This is useful to track how environmental
variables may be impacting irrigation
practices. Water use tends to increase
as light increases, for example. Further,
if you are interested in making a major
irrigation decision, such as changing to
cyclic irrigation, you can make that based
on data from your sensors.
If you are interested in automating
irrigation, very few companies provide
technology that makes this easy and user
friendly. A relatively new company, Mayim
(http://mayim.ag), provides technology to
automate irrigation using a variety of soil
moisture sensors. If you are interested in
building your own irrigation automation
system, the University of Georgia has
instructions for using an Arduino data
logger, moisture sensors and solenoid
valves to build an inexpensive system on
your own.
One concern among growers who wish
to automate irrigation using sensors is
that there is spatial variation in substrate
moisture in plants throughout the
greenhouse. For example, plants on the
edges of benches or near fans tend to dry
out more quickly than those in the center
of benches or near cooling pads.
Recent research conducted at the
University of Guelph explored whether this
variation impacts the ability to utilize soil
moisture sensors. In crops of basil and
bellflower, there were variations in soil
GREENHOUSE PRODUCT NEWS 15
moisture observed, both in a new, high technology
greenhouse and an older greenhouse. However, that
variation did not impact plant growth.
Stephanie Burnett is an associate professor of horticulture
in the School of Food and Agriculture at the University
of Maine. She can be reached at sburnett@maine.edu.
propagation trays
with results
http://www.mayim.ag
March 2019

Table of Contents for the Digital Edition of March 2019
