Soil Sensor | What is it and how do you use it?

A soil sensor is a device that measures three variables of the substrate (the nutrient soil on which plants are planted), namely:

• • The water content (%) as the amount of water (in percentage) in the substrate
  • The temperature (°C)
  • The salinity (mS/cm)

The salinity first measures the amount of salt in the substrate. This is called the bulk EC (mS/cm). The bulk EC is not yet of interest to a grower, as it does not show how much salt is available for a plant. For this, the grower needs the pore EC (mS/cm), which indicates the salinity available to the plant’s roots. To calculate this, the water content is needed.

Installation of the soil sensor

Place the soil sensor in the substrate. It is important that all three metal probes are fully embedded in the substrate and not sticking out into the air (as shown in image 1.3). When the metal probes are partly exposed to air, the substrate will not be fully measured.

 

The sensor only measures the substrate around the metal probes, not the entire substrate. Therefore, the positioning of the sensor is very important. If you place the sensor vertically at the top (see image 1.1), only the top part will be measured, where there are likely few roots present.

Therefore, place the sensor horizontally on the side of a pot (see image 1.2) if possible. This way, the substrate will be measured in the area where most of the roots are.

Do’s and Don’ts when installing a soil sensor

• • Install the sensor at the location in the substrate where you want to collect data.
  • Do not insert the sensor halfway into the substrate, as this will result in incorrect data.
  • Do not measure edge plants, as they are not representative due to the edge effect.

•  

 

Analyzing Data from the Soil Sensor

Every five minutes, the soil sensor measures and sends the temperature, water content, and EC values of the substrate to MyLedgnd.

Here, you’ll find an overview of how the values fluctuate throughout the day. Additionally, it is possible to discover trends in water content and/or EC values over longer periods.

 

Image 4: A trend of water accumulation: the substrate contains a higher water content over a longer period. This can be resolved by allowing the substrate to dry out for a longer time.

Image 5: A trend of salt accumulation: the salt content increases over a longer period, which can lead to plant stress. This can be resolved by “flushing” the substrate.

 

What conclusions can be drawn from the data?

The data from the soil sensor is very interesting to compare with:

 

• • Time: Recognizing trends over a longer period is particularly important for the salt content (pore EC) and the water content (%) of the substrate. This allows you to see if irrigation/watering is going as expected and helps prevent water or salt stress for the plant.
  • Air Temperature: By comparing the water content and the air temperature, you can gain insight into the effect of temperature on the rate at which the water content decreases. This provides an indication of the transpiration rate of a plant. Other factors that affect the transpiration rate include PAR/DLI and RH.

Air temperature, PAR/DLI, and RH also affect the salt content. For example, with a higher transpiration rate, the plant generally absorbs more water relative to salt in order to transpire. This leads to salt accumulation. Therefore, it’s important to regularly analyze the trends in pore EC and water content.

Advice from Ledgnd

The soil sensor provides insight into irrigation/irrigation practices in the greenhouse. By analyzing trends in water content and salt content, it is possible to minimize or even prevent plant stress. Furthermore, the soil sensor allows you to optimize irrigation/irrigation in the greenhouse.