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Soil moisture sensor-based irrigation reduces water use and nutrient leaching in a commercial nursery

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Marc W Van Iersel at University of Georgia
Marc W Van Iersel
R.M. Seymour
R.M. Seymour
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Matthew Chappell at Virginia Tech
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F. Watson
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SNA Research Conference Vol. 54 2009
Water Management Section
17
Soil Moisture Sensor-Based Irrigation Reduces Water Use
and Nutrient Leaching in a Commercial Nursery
Marc van Iersel1, Rose Mary Seymour2, Matthew Chappell1, Frank Watson3
and Sue Dove1
1 Dept of Horticulture, University of Georgia, Athens, GA 30602
2 Dept of Biological and Agricultural Engineering, University of Georgia, Athens, GA 30602
3 Cooperative extension, McDuffie Co., University of Georgia, Thomson, GA, 30824
mvanier@uga.edu
Index words: hydrangea, runoff, substrate water content
Significance to Industry: High quality irrigation water is becoming increasingly scarce
and it is becoming more important to use the available water efficiently. One approach
to more efficient irrigation is the use of soil moisture sensors to control irrigation. Soil
moisture sensors can detect when the substrate water content drops below a grower-
defined set point and can be used to automatically turn on the irrigation when needed.
Using this approach on a hydrangea crop in a commercial nursery from May 6 – July
23, 2008 resulted in large water savings: plots irrigated using standard irrigation
practices used 133,000 gallons during this period, as compared to only 23,300 gallons
for plots with soil moisture sensor-controlled irrigation. Excessive irrigation in the
control plots also resulted in more nutrient leaching: on June 13, substrate EC in control
plots was 0.94 mS/cm, while substrate EC in soil moisture sensors-controlled plots was
1.51 mS/cm. Thus, soil moisture sensors are a highly effective tool for reducing both
water use and nutrient leaching.
Nature of Work: Continuing population growth and increased urbanization threaten
water availability for agriculture, including greenhouses and nurseries. Thus, efficient
water use is increasingly important. More efficient irrigation practices not only reduce
water use, but also save energy and reduce leaching and runoff of fertilizer. In addition,
better water management may reduce the incidence of root diseases and may be used
for growth control (Burnett and van Iersel, 2008). One method for improving irrigation
practices is the use of soil moisture probes to open and close solenoid valves based on
the amount of water in the substrate. The objective of this work was to quantify water
savings that can be achieved using soil moisture probes for irrigation control.
Seven bays in an unheated greenhouse at a large commercial nursery were used for
this research in spring and summer of 2008. Each bay contained several hundred ‘Mini
Penny’ hydrangeas in #2 containers filled with a bark-based substrate. Irrigation in four
of the seven bays was controlled with a Moisture Clik irrigation controller (IL200-MC,
Dynamax, Houston, TX), which uses a dielectric soil moisture sensor (SM200) to
measure substrate water content. Since these controllers use a single probe, irrigation
in each bay was controlled based on the substrate water content in a single container.
SNA Research Conference Vol. 54 2009
Water Management Section
18
The irrigation controllers were set to come on when the substrate water content dropped
below approximately 0.20 m3·m-3. To prevent irrigation at night and keeping the foliage
wet, the Moisture Clik controllers were connected to a timer to power the controllers
from 8 am to 5 pm. Irrigation in the other three bays was controlled by nursery
personnel, according to their regular irrigation practices. Each bay was equipped with a
water meter, and irrigation volumes were recorded with dataloggers. Two soil moisture
probes (EC-5, Decagon, Pullman, WA) were installed in each plot and connected to
dataloggers (EM50, Decagon) to monitor the substrate water content. Substrate
solution EC was measured with a SigmaProbe (Delta T devices, UK) on June 13. Other
than irrigation, plants were produced using the standard cultural practices of the
nursery.
Results and Discussion: Water savings from soil moisture sensor-controlled irrigation
became apparent quickly (Fig. 1, top). During the first 10 days of the experiment,
control plants received approximately 6200 gallons/bay, while plants irrigated using the
Moisture Clik controllers received less than half of that amount. The Moisture Clik
controllers also proved to be the more reliable system, since control plants did not get
irrigated on May 17 and 18 (a weekend), during which the substrate water content in
control plots dropped to as low as 0.05 m3·m-3 (Fig. 2). A more detailed look at the
irrigation data shows that control plants were watered using a timer. On May 14,
irrigation in the control plots came on for 20 minutes every hour from 8 am to 12 pm.
Control plots received approximately 1200 gallons during this period, while Moisture
Clik-controlled plots received less than 200 gallons during this same period.
Differences in water use between the two treatments became larger during the summer,
as the frequency of irrigation in the control plots was increased. Over the course of the
experiment (May 6 – July 23), control plots received 133,500 gallons of water compared
to 23,270 gallons in Moisture Clik-controlled plots, a savings of 83%. Overall, substrate
water content in Moisture Clik-controlled plots was more stable than that in control plots
(Fig. 2). Moisture Clik controllers not only reduced water use, but also reduced
leaching. Substrate solution EC on June 13 was 0.94 mS/cm in control plots as
compared to 1.51 mS/cm in Moisture Clik-controlled plots, indicating that more fertilizer
had been leached out of control pots. Overall, these findings are similar to those of
Ristvey et al (2004), who showed that using TDR probes for irrigation control resulted in
water savings of 60-85% (with similar reductions in leaching of N and P) compared to
cyclic irrigation.
Shoots of 16 plants per plot were harvested at the end of the experiment, and no
differences in shoot dry weight or marketability were observed. However, these data
may not be completely reliable, since all plants were pruned in early July, which may
have masked differences in growth that could have occurred before then. An
unexpected side effect of the Moisture Clik controllers was a drastic increase in weed
pressure. We suspect that the excessive irrigation in control plots may have resulted in
a water-logged soil and low survival of weed seedlings. Reducing the irrigation volume
may have created more favorable conditions for weeds. Overall, this study shows that
soil moisture sensors can be used in commercial nurseries to control irrigation. This
SNA Research Conference Vol. 54 2009
Water Management Section
19
can result in major water savings, although the exact magnitude of savings is likely to
differ among nurseries due to differences in irrigation practices and crops. Future
research will also address whether soil moisture sensors can be used to impose a mild,
controlled drought stress that might reduce stem elongation and decrease the need for
plant growth retardants.
Literature Cited
1. Burnett, S.E. and M.W. van Iersel. 2008. Morphology and irrigation efficiency of
Gaura lindheimeri grown with capacitance-sensor controlled irrigation.
HortScience 43:1555–1560.
2. Ristvey, A.G., J. D. Lea-Cox and D.S. Ross. 2004. Nutrient uptake, partitioning
and leaching losses from container-nursery Production Systems. Acta Hort.
630:321-328.
SNA Research Conference Vol. 54 2009
Water Management Section
20
Figure 1. Comparison of irrigation volume using standard nursery practices (control)
and using a Moisture Clik irrigation controller. The Moisture Clik applies water based on
substrate water content. The top figure shows water use during a 10-day period, while
the bottom figure provides more detailed data for a single day.
SNA Research Conference Vol. 54 2009
Water Management Section
21
Figure 2. Substrate water content of hydrangeas irrigated using standard nursery
practices (control) or irrigated using a Moisture Clik irrigation controller as measured
with EC-5 soil moisture probes over a 2½ month period. Note that the Moisture Clik
results in much more stable water contents in the substrate.
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