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The horizontal orientation of the sensor ensures the measurement is made at a
particular soil depth. The entire sensor can be placed vertically, but because soil
moisture often varies by depth, this is not usually the desired orientation. To
position the sensor, use a thin implement such as a trenching shovel to make the
pilot hole in the soil. Place the sensor into the hole, making sure the entire
length of the sensor is covered. Press down on the soil along either side of the
sensor with your fingers. Continue to compact the soil around the sensor by
pressing down on the soil with your fingers until you have made at least five
passes along the sensor. This step is important, as the soil adjacent to the sensor
surface has the strongest influence on the sensor readings.
Removing the Sensor
When removing the sensor from the soil, do not pull it out of the soil by the
cable. Doing so may break internal connections and make the sensor unusable.
What is Volumetric Water Content?
In very simplified terms, dry soil is made up of solid material and air pockets,
called
pore spaces
. A typical volumetric ratio would be 55% solid material and
45% pore space. As water is added to the soil, the pore spaces begin to fill with
water. Soil that seems damp to the touch might now have 55% minerals, 35%
pore space and 10% water. This would be an example of 10% volumetric water
content. The maximum water content in this scenario is 45% because at that
value, all the available pore space has been filled with water. This soil is
referred to as being saturated, because at 45% volumetric water content, the soil
can hold no more water.
Videos
View videos related to this product at
www.vernier.com/sms-bta
Calibrating the Sensor
Optional Calibration Procedure
It is not usually necessary to perform a new calibration when using the Soil
Moisture Sensor. The Soil Moisture Sensor has a stored calibration that will give
good results. If, however, very accurate readings are needed, a calibration using
the sample soil type to be measured is recommended. Two methods are
described below. Method 1 is faster and easier, but potentially less accurate than
Method 2.
Calibration Method 1: Two-Point Calibration
This is the faster and easier of the two methods, but is potentially less accurate.
1. Dry the soil in a drying oven at 105˚C for 24 hours.
2. Obtain a water-tight container that is large enough to fully insert the sensor
with room for at least 2 cm on all sides. A plastic shoe box or similar works
well.
3. When cool, break up any large clods until all soil fits through a 5 mm
screen.
Soil Moisture
Sensor
(Order Code SMS-BTA)
The Soil Moisture Sensor is used to measure
the volumetric water content of soil. This
makes it ideal for performing experiments in
courses such as soil science, agricultural
science, environmental science, horticulture, botany, and biology. Use the Soil
Moisture Sensor to:
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Measure the loss of moisture over time due to evaporation and plant uptake.
l
Evaluate optimum soil moisture contents for various species of plants.
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Monitor soil moisture content to control irrigation in greenhouses.
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Enhance your Bottle Biology™ experiments.
Note:
Vernier products are designed for educational use. Our products are not
designed nor are they recommended for any industrial, medical, or commercial
process such as life support, patient diagnosis, control of a manufacturing
process, or industrial testing of any kind.
Compatible Software
See
www.vernier.com/manuals/sms-bta
for a list of software compatible with the
Soil Moisture Sensor.
Getting Started
1. Connect the sensor to the interface (LabQuest Mini, LabQuest 2, etc.).
2. Start the appropriate data-collection software (Logger
Pro
, Logger Lite,
LabQuest App) if not already running, and choose New from File menu.
See the following link for additional connection information:
www.vernier.com/start/sms-bta
Using the Product
Positioning the sensor
Figure 1 shows the proper placement of the Soil Moisture Sensor. The prongs
should be oriented horizontally, but rotated onto their side, like a knife poised
to cut food, so that water does not pool on the flat surface of the prongs.
Figure 1
