How to understand your soil moisture data
How do you interpret the measurements from your soil moisture sensor? How accurate is the data? Why can the moisture level be different from what you expect to see? And how can it be that two sensors next to each other are not showing the same moisture levels? Read below to understand the “why” and see the end of the article for tips and tricks on what you can do to get the most reliable data out of your field.
Understanding the measurements of your soil moisture sensors is easy. Whether you are using the Sensoterra Index (SI) or Volumetric Moisture Content (%), you can use the data sheets on our soil calibration page to see which values indicate wet and dry zones for every soil type. Use these recommended values when you define your sensor's high and low setpoints - this will make it easier for you to make an irrigation decision.
When it comes to sensor accuracy, we are proud of our robust and reliable technology which measures soil moisture with an accuracy of within ±1.5% when used in the appropriate soil type. However, the accuracy of your data also depends on the soil characteristics in the exact spot of installation, if the sensor is in full contact with the soil and how much your soil type varies from the chosen soil calibration.
It is therefore still likely that, in a field of sensors, you may see varying soil moisture measurements. This is completely normal and can be explained by the amount of rocks and roots in the ground and the variation in soil composition across the field.
Imagine these 5 examples: You have 5 sensors installed in the exact same soil type, but they all show different measurements. The soil itself will absorb similar amounts of water in each example, but the sensors will also include the surrounding rocks, roots or air in the measurement. Therefore you can expect the measurements in each example to be slightly different.
Factors that can influence readings. Rocks, roots and air around soil might offset the reading - but the sensor will still work. But air covering the measuring pins will result in a 0% reading.
This is why we recommend you to use a system of sensors, rather than relying on a single data point. Using a system of sensors enables you to look at the overall trends of your field, taking field variations into account. Looking at the average soil moisture trends of your field, the data reliability goes up, and you will be better suited to decide when or when not to irrigate your field.
Example of field moisture variance. Soil moisture can vary across a field.
Tips and tricks
- Use a system of sensors
This is the best way for you to ensure reliability of the data coming out of your field. Use the average of the different measurements to get the best general overview of soil moisture in that field.
- Good installation practice is key
- If you encounter hard resistance when hammering the sensor into the ground, try moving the sensor to a new spot - even if it is only 10 cm away, it can make a big difference. Seeing how different the soil can be - even at small distances - also explains why the readings can vary slightly.
- Ensure that your sensor has good contact with the soil. The sensor should be sturdy in the soil, not wiggling.
- Use the right calibration for your soil
Using wrong calibrations for your soil, will likely offset the data, however you should still be able to see the overall trends.