Soils vary greatly. Because of this, soil moisture sensors have to be calibrated in order to correctly indicate when the soil is full of water or is lacking. Semios has developed a system that will automatically calibrate the probes based on data received from the probe. However, the soil must reach saturation in order to provide the needed data to calibrate. Saturation is when the soil is filled to the point that it has excess water. When irrigation ceases, extra water will drain downwards in the soil. It is pretty easy to see when your soil is saturated by looking for the correct shape of trendline on your soil moisture graph.

The correct shape is called a drainage tail. Drainage tails are distinguished by a upward refilling of the soil profile and then a rapid downward trend with a “swoop” where the trend line levels out. This is representative of a soil that is saturated, drains quickly as the water is shut off and then stops draining as all the excess water leaves and the soil is left holding all the water it can retain.

In order to automatically calibrate, the system will need to see 3 of these events within 14 days. The best practice is to irrigate until you think your soil is full. Shut off the water and watch to see if a drainage tail appears. It will take a few hours before you see it. If it does not appear, irrigate some more until it does. If you do see a drainage tail, your job is done until the next time you irrigate. Just be sure you irrigate until the soil is full the next time as well. If you would like to calibrate your probes even faster, consider irrigating your field once a day until it is saturated for three days in a row.

After your probe is calibrated, you are all set. You can trust that the data is accurate and that 100% means that your soil is filled to its max capacity. That being said, the computer doesn’t stop there. Our system will continue to watch the data and look for small changes that come as the season progresses so that it can continue to fine-tune the calibration.