Vernier SMS-BTA Getting Started And Quick Manual

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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 Proce dure

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 Me thod 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:

l Measure the loss of moisture over time due to evaporation and plant uptake.
l Evaluate optimum soil moisture contents for various species of plants.
l Monitor soil moisture content to control irrigation in greenhouses.
l 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-b ta

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

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4. 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.

5. Connect the Soil Moisture Sensor to the interface and start the data­collection program.

6. Pour the soil into the container position the sensor as shown. 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.

7. 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 five passes along the sensor.

8. Add more soil on top of the compacted soil so that the sensor is buried at
least 3 cm below the soil surface.

9. Compact the soil again using a clenched fist.

10. Enter the calibration portion of the data-collection program and record the
voltage reading from the sensor. N ote: In this method, entering the
calibration portion of the program is used only to obtain a raw voltage
reading from the sensor. You will not be completing a typical 2-point
calibration in the software.

11. Use a soil core tool to take three volumetric soil samples adjacent to the
sensor.
a. Insert the sampling cylinder fully into the soil.
b. Remove the soil core.
c. Dispense the core into a drying jar.
d. Weigh and record the mass of the jar plus soil.
e. Repeat Steps a–d for two additional core samples.

12. Remove the sensor from the soil.

13. Decide on a standard volume of distilled water that will increase the water
content by 3 to 10% for each measurement. If you are unsure about the
amount of water to add, measure the volume of soil you are using. Use a
volume of distilled water equal to 5% of the volume of the soil.

14. Add one aliquot of distilled water to the soil in the amount decided upon in
Step 13. To avoid clumping, add the water in small amounts, mixing
thoroughly.

15. Replace the sensor in the soil. 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 five passes
along the sensor.

4. Connect the Soil Moisture Sensor to the interface and start the data­collection program.

5. Pour the soil into the container and position the sensor as shown. 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.

6. 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 five passes along the sensor.

7. Add more soil on top of the compacted soil so that the sensor is buried at
least 3 cm below the soil surface.

8. Compact the soil again using a clenched fist.

9. Enter the calibration routine of your program. Keep this first calibration
point and assign a value of 0. This represents 0% volumetric water content.

10. Remove the sensor from the soil.

11. Determine the approximate volume of soil used. This can be done by
packing it into a large, graduated beaker.

12. Return the soil to the calibration container.

13. Obtain a volume of distilled water that equals 45% of the volume of the
soil. If, for example, you used 3500 mL of soil, you would obtain 1575 mL
of distilled water.

14. Add the distilled water to the soil and mix well.

15. Position the sensor in the wet soil, again making sure the sensor is
completely covered and that there are no gaps between the soil and the
sensor.

16. Keep this second calibration point, assigning it a value of 45. This
represents 45% volumetric water content.

17. Your sensor is now calibrated for this soil type. If you are using LoggerPro
3, you can save the calibration directly on the sensor. If not, you may want
to record the calibration values for future use.

Calibration Me thod 2: Multiple-Point Calibration

This method is more accurate, but requires more time and effort than Method 1.

1. Obtain and number 12 drying jars. The jars must be able to withstand the
105°C temperature of the drying oven.

2. Weigh and record the mass of each jar.

3. Prepare the dry soil by breaking up large clods until all soil fits through a
5 mm screen. N ote: The soil should be fairly dry, but does not need to be
oven-dry for this method.