This research evaluated the use of soil moisture and matric potential sensors to better understand plant available water in engineered landscape soils. Sensors were installed at two sites with the same engineered soil blend but different conditions. The sensors measured volumetric moisture content, temperature, electrical conductivity, and matric potential. Preliminary results showed that moisture sensors could inform irrigation systems but more work is needed. Temperature and moisture patterns varied between sun and shaded sites. Further analysis will explore how fertilization and plant water stress impact readings to refine soil blends and sensor use.

1. Using Soil Water Sensors to Evaluate Plant Available Water
In Engineered Landscape Soils
Kevin Donnelly CH, Midwest Trading Horticultural Supplies Inc.
Introduction
Initial feedback and next steps
ResultsMaterials and Methods
Sensor images from Metergroup.comObjectives
• Evaluate use of moisture and matric
potential sensors
• How can sensors be used as tool for
irrigation systems
• Use plant available water data to inform
engineered soil design
In soil science, plant available water is
characterized through a moisture release curve
that plots moisture content with matric potential.
Volumetric moisture content is a measurement of
the total volume of water held in a soil. Matric
potential is a measurement of how tightly the
water is held to the soil surface.
Unlike naturally occurring mineral soils,
engineered soils can vary drastically from one
project to another; due to site conditions, raw
material inputs and recipe. There is little
understanding of plant available water in these
systems. However there is an opportunity with
engineered soils to tailor soil blends to meet
project requirements.
This research is the first step in an extensive
research program to better understand site
conditions and plant available water
characteristics of engineered soils.
This research was conducted at the Gardens at Ball
Horticultural Company in West Chicago IL. Two
raised bed sites were selected that use the same
engineered soil blend.
Site 1 is a perennial bed that was in the shade and
prone to flooding.
Site 2 is a vegetable bed at a higher elevation and in
full sun. Both are on drip irrigation.
Site Selection
First season research feedback
• Crops were under irrigation, so higher tensions
were not measured
• Moisture sensors are likely a better fit for
automatic irrigations systems though more work
is needed.
• EC value in sensors fluctuated a lot and can be
used for making fertilization decisions
• Drip irrigation may have caused inconsistent
readings
Next Steps
• Reviewing data set from summer 2019. 600,000
data points.
• How did fertigation impact EC readings
• Identify conditions that caused plant water
stress
• Map impact of temperature on dry down
patterns
• Run controlled replications in greenhouse with
PM35
• Look at modifications to blend and chart impact
on plant available water
• Evaluate other sites during summer 2020
• Expand use of moisture/temp and EC sensors for
additional sites
Sun vs Shade Site.
The shallow depth in the sun had dramatic swings
in temperature of 10-14 Degrees F during the day.
Deeper soils and those in the shade had much
more moderate soil temperatures. The Sun site is
open and more exposed to heat loss during the
night resulting in lower night temps for 4” vs 8”
depths.
Moisture release curve
For each site, T21 and T12 sensors were installed
together at 4” and 8” depths. The T8 sensor was
placed at 6” depth. Cables were run though garden
hose and PVC up to the data logger to protect against
damage. The five sensors were connected to the ZL6
data logger. Measurements were taken at 5min
intervals and uploaded to a Zentra Cloud platform.
The system was installed May 24 and data was
collected through Oct 1st
Teros 21 measure moisture content in a ceramic disk
with a known release curve and converts to tension
T8 is a sealed column of water with a permeable
ceramic cap that allows water to be pulled through
creating a tension measurement
Teros 12 measures volumetric moisture content,
temperature and EC.
20%
25%
30%
35%
40%
45%
50%
55%
1 10 100 1000
PM35 Moisture Release Curve
65
70
75
80
85
90
95
24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18
TempeatureinF
Hour of Day 24hr
Soil Temperature
Sun 4" Sun 8" Shade 8" Shade 4"
Teros 12.
Moisture,
Temperature, EC
Teros 21.
Matric Potential,
Temperature
T8.
Matric Potential,
Data from T21.
Saturated of 10kPa. Demonstration release pattern
for pm35. Significant volumetric water available
down to 35% moisture. No measurements at higher
tension due to irrigation ran heavy rain.