The Waterscout SM100 soil moisture sensor by Spectrum Technologies Inc. measures the soil moisture content as a percentage of the soil volume. Due to the dimensions and pointed tip, the sensor can easily be applied in the soil or in another medium.
Maintaining a healthy soil moisture and water balance is essential for producing high quality plants. Under-watered plants suffer from nutrient deficiencies, stunting and wilting. Conversely, over-watered plants are more susceptible to disease pressure and less tolerant of dry conditions later on in their life cycle.
The sensor should be located in the effective root zone and at locations that will give a representative picture of the soil water status of the field. Areas of the field planted to different crops or with significant differences in factors such as topography or soil type should be considered unique soil moisture environments.
Selecting a site which receives the least amount of water from the irrigation system will tell you when that area becomes critically dry and is in need of attention. Typically, one or two sensors should be installed in the root zone. A single sensor should be placed in the middle of the root zone. When two sensors are installed at a single site, it is recommended to place one sensor at the top of the root zone and a second at the bottom.
An advantage of installing multiple sensors is it allows you to see how well irrigation and rainwater is moving through the soil profile. The SM100 is most sensitive to the soil adjacent to the sensor. Therefore, good contact between the soil and sensor is important. Stones and air pockets next to the sensor will affect the accuracy of the readings. We recommend not to install the sensor in or near metal.
The following method is recommended to install the SM100 at multiple different heights:
- Drill a hole of 10 to 15 cm wide, to the depth where you want to measure.
- Place the Waterscout sensors horizontally in the side wall of the borehole, at the desired heights. Make sure that the blue sensor element is positioned straight, so that no water droplets can form on top of it.
- Refill the borehole with the soil removed. Make sure to return the correct soil layer in its original order.
Comparing the SM100 to the Watermark sensor
Both the SM100 and the Watermark sensor measure soil moisture. However, there are some differences that we can point out. The SM100 measures the soil moisture content as a percentage of the soil volume, whereas the Watermark sensor actually measures how much effort is required by a plant to extract water that is available from the soil.
The SM100 is easier to install and move compared to the Watermark sensor. The Watermark sensor is often used by research companies that require highly accurate sensor data. Finally, the Watermark sensor that Crodeon offers includes three Watermarks while the SM100 only measures in one spot. Adding multiple SM100 sensors requires using up more connectors on your Reporter.