By Jonathan Sercu

Comparing the Watermark sensor to the WaterScout SM100

Comparing the Watermark sensor to the WaterScout SM100

Both the WaterScout SM100 and the Watermark sensor measure soil moisture. However, there are some differences we can point out. In this article, we'll take a closer look at the two sensors, go over the main pros and cons and provide some tips on how you can quickly get started yourself.

irrigation sensors

Measurement principle

The WaterScout SM100 measures the volumetric water content as a percentage of the soil volume. For example, if we take 1 liter of soil consisting of 0.25L of water, 0.25L of air and half a liter of soil matter, the WaterScout will indicate 25%.

The Watermark, on the other hand, measures how much effort a plant has to make to extract available water from the soil. The Watermark readings are expressed in kilopascals. A higher reading means that the soil is drier, and a plant therefore has to make more effort to extract water from the soil. The following breakdown is used as a general guideline:

  • 0-10 kPa: Saturated soil
  • 10-30 kPa: Soil is sufficiently wet (except coarse sands, which is already starting to lose water here)
  • 30-60 kPa: Usual limit to start irrigation (most soils)
  • 60-100 kPa: Usual limit to start irrigation in heavy clay soil
  • 100-200 kPa: Caution. Soil is starting to get dangerously dry to reach maximum production

Response speed

A known disadvantage of the Watermark sensor is that it reacts rather slowly during the drying process. The measurements can sometimes be delayed by up to a day if the soil in which the sensor is located dries up. The WaterScout SM100, on the other hand, responds almost in real time.

WaterScout SM100

Temperature compensation

In the past, what used to be mentioned as a disadvantage of the Watermark was its dependence on the soil temperature. That is why it is very important to also measure the temperature of the soil and then use this value to adjust the measurements of the Watermark.

Crodeon solves this by automatically applying the calibration with a soil temperature sensor on the Watermark adapter. We use the formula developed by Dr. Clinton C. Shock. In this setup, the sensor is therefore no longer dependent on soil temperature. The WaterScout SM100 is not temperature sensitive.

Watermark sensor

Dependence on the soil type

The main advantage of the Watermark is that it is independent of the soil type, as the sensor measures the actual suction or soil water tension. This is also the main drawback of the WaterScout SM100, which requires from the user a good knowledge of the soil.

It is recommended to start measuring with the SM100 early in the spring to determine the field capacity of the soil. You can then consider that measurement as a reference for the rest of the season, an indication of how much water the soil can hold. This can differ greatly depending on the soil type. For example, a clay soil can retain much more water than a sandy soil.

Combine with other measurements

As you can see each sensor really has its advantages and disadvantages. The good news is that both sensors are plug & play compatible with the Crodeon Reporter.

Crodeon Reporter

You can connect the sensors at the same time, but it is also possible to read several identical sensors with one device. This can even be done in conjunction with other sensors for measuring weather conditions such as temperature, humidity, leaf wetness, wind or rain.

Those who want to go one step further can, for example, measure the pressure on a water pipe, measure the flow rate with a water meter or the groundwater level with a level sensor. Visit our webshop to view all compatible sensors.

Controlling irrigation

Finally, our technology also makes it possible to control an irrigation system. We offer a control module with six built-in relay connections for this. This gives you the option of starting a pump or opening a valve via PC or smartphone at the touch of a button. Do not hesitate to contact us for more information about the possibilities.