Application of Soil Moisture Sensor

Precision irrigation increases yields, reduces labor and conserves water. Irrigation scheduling using soil moisture sensors, especially for agriculture, is one of the easiest and most cost-effective ways to conserve water and reduce costs. There are many soil moisture sensors available today and understanding the basic differences between them will make it easier for you to choose the right sensor for your application.

Types of Soil Moisture Sensors

The most common types of soil moisture sensors include plaster blocks, tensiometers, capacitive, volumetric and neutron probes. These sensors measure soil tension or measure volumetric water content when placed in the soil.

Soil moisture meter for measuring tension

These sensors measure tension in the soil and report how much energy plants need to draw water from the soil. When water is plentiful, plants absorb water more easily, and as the soil dries out, plants work harder to absorb water. The unit of measurement is the centibar. When the soil is full of water, the tension in the soil is close to zero, and the mbar increases as the water evaporates, runs off, and is used by plants. When the mbar reaches a certain value, the timing of watering depends on the plant and the soil.

Think of a plaster block soil moisture sensor as two electrodes buried in plaster. When water enters a plaster block, it becomes less resistant. These blocks have two wires coming out of the block and connecting to a handheld reader or data logger.

This data logger provides a readout indicating when to water based on the plant and soil type. It takes some time for the plaster to absorb moisture, so these sensors will lag and will wear out over time, so you’ll need to replace them every two seasons. They are relatively easy to install and inexpensive.

Advantages and disadvantages of soil tension sensor

The tensiometer is accurate and affordable. The mbar is easy to read on the dial, so it’s easy to know when to water. The challenge with them is that they require more regular maintenance than regular volume or capacitance probes.

If you miss a refill or have an incorrect refill, you will get wrong data. Also, these devices only have one depth they report, so to get the same number of 48″ root zone readings as other probes, for example, you’d have to buy, install and maintain 12 tensiometers at every site you want to monitor soil moisture . As you can see, this is not a scalable way to measure soil moisture throughout an operation, like a sealed probe would be.

Capacitive Soil Moisture Sensor

These sensors measure the amount of water in the soil by releasing an electrical charge into the soil, which in turn measures the soil’s dielectric constant. Soil has different dielectric constants depending on the amount of water in the soil. This reading occurs quickly and can be transferred to software for use in irrigation planning. Growers don’t have to drive around to look at the dial; they get all the information they need on their computer, phone, tablet or tablet.

Advantages and disadvantages of capacitive sensors

These sensors are durable, robust and low maintenance. They also provide soil moisture measurements at different soil depths if you prefer. You can buy them in various lengths (great for deep-rooted trees) and attach sensors to each 4-inch section to watch water move through the soil. Some also provide soil temperature and soil salinity and fertilizer measurements.

They can be connected to JXCT software, providing the ability to view soil moisture remotely from any internet-connected device. These devices are more expensive, but the added value you get outweighs the added cost of makeup.

Soil moisture sensors provide a window into the water at multiple points in the root zone without the need to take multiple samples or use a backhoe or other digging equipment to look below the soil surface.

Conclusion

We know the water content of the soil at any point in time. We track trends over time; every year is different, and even small differences can influence how we choose to irrigate for the coming year. Some capacitance probes have temperature sensitive inputs and report soil temperature to help time our chemical injection. It’s a tool that provides near real-time insight into what our soil profiles are doing.