Both the WaterScout SM100 and the Watermark sensor measure soil moisture. However, there are some differences between these water measurement sensors that 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.
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 sensor, 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, the plant has to make more effort to extract water from the soil. The following breakdown for this water measurement sensor is used as a general guideline:
- 0-10 kPa: Saturated soil
- 10-30 kPa: Soil is sufficiently wet (except coarse sands, which are 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
A known disadvantage between these water measurement sensors is one of the Watermark sensor, 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.
In the past, what used to be mentioned as a disadvantage of the Watermark sensor 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 water measurement sensor WaterScout SM100 is not temperature sensitive.
Dependence on the soil type
The main advantage of the Watermark sensor 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 the user to have a good understanding of the soil.
It is recommended to start measuring with the SM100 early in spring to determine the field capacity of the soil. Later you can take 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, clay soil can retain much more water than sandy soil. Choosing between these two water measurement sensors really depends on where you want to use them.
Combine with other measurements
As you can see each sensor really has its own advantages and disadvantages. The good news is that both sensors are plug & play compatible with Reporter.
You can connect both the water measurement sensors at the same time, it is also possible to read several identical sensors with one device. This can even be done in combination 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 besides the Watermark sensor and the WaterScout SM100.
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.