Soil Moisture Probes
Updated: Jul 15
Soil moisture probes are vital in determining when and how much water and nutrients to apply to your crop with your subsurface irrigation system.
One of the frequently asked questions we get is how to properly place a soil moisture probe so it is giving relevant information on the amount of moisture that is being put in the soil. In this post, we discuss how to properly install a soil moisture probe, explain the variety of models available for use, and the benefits of soil moisture probes and why they are a great tool in your toolkit.
How to Place a Soil Moisture Probe
To start with, it is really important to dig down and find the drip tape emitter. In a field that has 60-inch drip line spacing, and there is an emitter every 24 inches, we find one emitter then measure down the line and mark out the next two emitters. We then pick an emitter, and measure 6-8 inches out, and 6-8 inches parallel to the drip line and place our soil moisture probe. If we put the soil moisture probe right between the two 60-inch drip lines, or put it right beside the emitter, it will not be representative to the moisture level in the soil.
Different Types of Soil Moisture Probes
The Sentek soil moisture probe system has a tapered probe and we use a dry install method. It has little indentations every six inches where is takes readings from. There is circuitry inside the probe, so it is important to be somewhat gentle with it. The probe also contains a small modem that transmits data to the cloud where we can access it. This system is fairly simple to install using a tapered drill bit. (See video for demonstration)
The Aquaspy soil moisture probe is a 48-inch probe that takes readings every four inches. It is filled with circuitry, so it is wise to be somewhat careful when placing this. It connects to a telemetry unit that has a solar panel on it. This is not a tapered probe, so we use a drill bit and make the hole a little bigger than the probe size. Next take the dirt out of the hole and make a slurry out of it, and then push the probe down into the slurry; this is called a wet install.
The Irrometer soil moisture probe is the simplest system there is. It is all manual. It has a gypsum filled tip; we fill up the middle part with liquid and put a vacuum on the end to extract all the air. This is installed by simply pushing a regular soil sampling probe into the ground, and then follow it with the soil moisture probe. As the soil dries out, it will create a vacuum on the vacuum gauge. You have to manually go to the field and read the system, but it is very inexpensive and you can get different depths of probes, anywhere from four to 48-inch depths. We recommend having multiple of these out in your field to see what’s going on.
Also by Irrometer is the Watermark sensor. These have gypsum filled blocks that we soak in water ahead of time to get them to their full capacity, then use a regular soil probe to drill a hole and push the probe into the ground. There are wires that connect to telemetry and send data to the cloud where we can access it and create charts and graphs that help us understand how much moisture is the soil. You can get different lengths of these probes to measure moisture at the depth you want. These are inexpensive sensors; the cost is in the telemetry and equipment needed to communicate to the device.
(pictured above are examples of AquaSpy and Sentek soil moisture probes and a Watermark sensor.)