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How to Get Started with Soil Moisture Sensors

Updated: Mar 27

Very often people approach us by asking how good our substrate moisture sensors are, ignoring the fact that knowing how to use a sensor is more important. I don’t mean the quality of the sensor does not matter, however, there are several other important factors that can affect the overall performance of a soil moisture monitoring system. Just for your information, we developed the first model of the APAS T1 over fifteen years ago and over time it evolved to become the sensor it is today.

To be able to successfully perform an irrigation scheduling scheme, we need to combine "good sensors" with "science" and "experience". I always say sensors are dumb, we are not! A good sensor is not perfect, but it is reliable and accurate enough to be used in irrigation scheduling.

Ok, let's say you have received your APAS T1 substrate moisture sensors and want to use them for irrigation water management in your backyard garden, orchard or potted plants. Here are some steps you should take, in order to perform a successful plan:

  1. Learn the hardware and software

  2. Install the sensors correctly

  3. Collect data and observe plants response

  4. Analyze data and improve your current approach

1) Learn the hardware and software

I cannot emphasize enough how important it is to start by reading the user manuals of your sensor and readout device! We have made it so easy to use our sensors and readout devices. However, this does not mean you should skip reading the user manuals specially if you’re hoping to unlock the full potential of the sensor.

There are guides, warnings, and details that can help you extend the life of your sensors and increase measurements accuracy. So, please learn how to use the hardware (e.g. sensors and reader) and software (e.g. mobile app and possibly Windows app) by reading the documents that are available on our website. To understand the instruments even better and maximize their benefits, please also make sure to explore our research and blog articles, and social posts.

2) Install the sensors correctly

In my opinion, this is the trickiest part that most people take it wrong. Sensor installation options generally depend on the sensor, your needs and the type of medium you are using. No installation can be perfect, but there are ways to avoid errors when installing a sensor. The easiest way to make sure things have gone as planned is to install the sensor, water the soil and check the readings. You can tell if the installation is done properly if the readings are within an acceptable range (they’re not too high or too low for a specific soil). Sometimes, you need some level of experience to be able to spot installation errors, so just give yourself time to learn if you are new to using sensors.

You might have heard about how air gaps can affect soil moisture sensor measurements. To guarantee good installation is more than just avoiding air gaps. Where to install a sensor is also important. Imaging you've got only a few soil moisture sensors because of your limited budget, and have many plants to irrigate.

"Which pots should I choose for sensor installation", you may ask. One of our customers is managing irrigation in a three-acre orchard using only five (5) soil moisture sensors with no problem. I know someone who has installed over forty (40) sensors in smaller orchard and he thinks he needs more!

The first step to determine where to install sensors is to define your irrigation zones. An irrigation zone includes all the plants that have similar water demand or normally irrigated at the same time. You will need at least one sensor per irrigation zone.

As I said, water needs must be similar. Mixing young and old plants (at different point in their growth stage) is never a good idea. This is because they have different watering requirements. For example, if you have two plants with different water needs, they need to be in two different irrigation zones.

The second step is to choose spots (or plant pots) that are representative of the rest of the irrigation zone, or where you expect to run out of water the fastest (critical points).

I have previously published several articles that can help you with sensor installation. You can find them on our blog.

3) Collect data and observe plants response

You may think, ok I’m going to install the sensors and get started with using them for irrigation scheduling. This might not be a good idea. Before getting into that stage, you need to evaluate your current irrigation scheduling practice and identify its weaknesses. This will provide an invaluable insight that allows you to appreciate the sensors more.

Determine dry and wet thresholds and maintain soil moisture between the limits

Another important reason why you need to take this step is that you need to establish what is called “Wet and Dry Thresholds”. You will be collecting soil moisture data and at the same time observe plants response to watering. After a while, by combining the two you will be able to develop the threshold lines that work for you and your plants.

Thus, after the installation, for a while you should only collect data and continue with your current practice of water management.

4) Analyze data and make a plan

This is the last and most critical stage. You need to transfer the data you have collected to a spreadsheet and graph them. Looking at the graph and the trend of soil moisture, you can learn a lot. As I mentioned above, you’ll be able to find wet and dry threshold lines for your new irrigation scheduling scheme. These are the lines that you should stick to and make sure soil moisture will stay between them at all time.

So, make a new plan based on the results of your analysis, and start using soil moisture sensor data for improving your irrigation water management.

Example: Shasta Gold Mandarin orchard

Look at the picture below. This data was collected by one of our customers in a Shasta Gold Mandarin orchard. S1 thru S4 are soil moisture sensors. They have five different irrigation zones.

APAS T1 soil moisture data from a Shasta Gold Mandarin orchard. S1 thru S4 are soil moisture sensors.

You can clearly see steps 3 and 4 on this chart. They moved from a terrible water management (left side of the chart) to one that works (right side of the chart). What you see on the left half of the chart is their original irrigation plan. You can see that they were under-irrigating their trees. This resulted in some level of damage to the trees. Luckily, the damage was not permanent. You may ask why they didn't irrigate enough? The answer is that if you're not using sensors, it won't be easy to tell. In addition, the water is expensive in southern California and you don't want to get a water bill that is going to make you bankrupt!

Shasta Gold Mandarin orchard in southern California

Anyway, after a few months of observation and data collection they analyzed the data and came up with a better plan. The new plan resulted in the right half of the graph. They determined the appropriate dry and wet thresholds for their orchard and irrigated in a way that maintained soil water above the dry threshold. There were a few rainfall events that caused the soil moisture content to exceed the wet threshold, but that was beyond their control and not as important as avoiding plant water stress.


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