Farmers, gardeners, and folks with indoor potted gardens all appreciate the right watering method (not too much or causing a drought to your plants).
Knowing when to water is often a factor though, since there’s rain, irrigation, etc.
This is exactly why many professional farm operations and backyard gardeners use soil moisture sensors. Soil moisture sensors will not specifically tell you how much water is in that soil but they do report changes to the soil that indicate water is being used and that the soil is drying out.
There are many different types of soil moisture sensors on the market and it pays to know your options, how the sensor works and how to read the report.
In this Article: Below is a soil moisture sensor complete user guide to help those interested in potentially purchasing a sensor understand what they are buying.
What Is a Soil Moisture Sensor?
The sensor measures the amount of water content in the soil, and it can also show how much water is stored in the soil.
For the sensor to work, it needs to be in contact with the soil.
Knowing the volume of water content in the soil is useful to professional farmers who need scientific information to have a successful harvest season.
It can also be useful to scientists in the soil, environmental and agricultural fields who conduct experiments, as well as in horticulture, biology and botany.
How are Soil Sensors Used?
There are three types of approaches to soil sensors.
All three are contained within this soil moisture sensor full user’s guide.
What Is Single-Point Measurement?
Single-point measurements refer to the use of sensors to assess water tables at one specific location, at a specific depth.
The downside is that you have to dig a hole large enough to cover each sensor.
That can cause plant damage and disturb the soil. However, you may only need one sensor for your land.
If all you need is a water content measurement, one sensor can measure the water content in a footprint of 600m in diameter.
What Is a Multi-point profile?
Multi-point profile measurement is accomplished by inserting multi-point probes which are single-point sensors in a housing.
This allows for multiple points to be inserted at a single time.
Bad News – The one downside is that you have to insert the unit into the soil using a power boring tool.
What Is Continuous Profile Management?
The third kind of sensor is continuous profile management.
In this case, antennas act as sensors, providing measurement monitoring across the entire area and not just where the sensors have been positioned.
This gives a very clear picture of a moisture profile.
This can often be put in place with a pilot rod but a boring tool could be used in some circumstances.
There will be differences in cost for the three types of soil moisture sensors but more money may be spent on the installation based on how much work it is to get it in the ground.
Outside of the three types of soil moisture sensors, you also have more specific types of sensors that measure water in other ways.
Those are:
- Tension meters
- Gypsum blocks
- Capacitance
- Volumetric
- Neutron Probes
- State soil sensors
Each method functions differently by measuring a different aspect of the soil and its relationship to the water in the land.
Some measure the volume of water, while other measure tension of the soil or measure some electrical characteristic.
Are Soil Sensors Accurate?
Agricultural researchers have found that a sensor can effectively measure water in the soil. A sensor with calibration that is specific to the soil being studied is much more accurate than factory calibration equations.
Extension offices generally recommend using a sensor with neutron probes that are deemed most accurate for measuring soil moisture levels. A neutron probe is a volumetric sensor.
When measuring the hydrogen content of the soil, it is a good indication of water volume.
When measuring soil water volumetrically, volumetric sensors are probably the easiest to conceptualize, as soil water content is being measured directly.
In addition to the neutron moisture probe, di-electric and heat dissipation sensors also fit in this category, however, they all have different functions.
Di-electric sensors measure the soil moisture content through an electrical sensing unit while measuring property of the soil whereas heat dissipation measures the heat dissipated from itself versus the surrounding soil for moisture temperature.
Tensiometers are similar to the previous sensors but function to use the soil tension in order to determine water levels. Tensiometers are a vertical tube filled with water inserted into the soil to the study depth.
Tensiometers have a porous tip, the clay soil draws the moisture out of the water-filled tube, effectively creating a vacuum. The strength of the vacuum within the tube indicates how dry the soil is, greater vacuum indicates dryer conditions.
Solid-state Sensors
Solid-state sensors are devices like granular matric sensors and gypsum blocks.
They work with two electrodes to measure electrical resistance in the soil.
More water will result in less electrical resistance.
The most basic types of sensors would be hygrometers, which measure soil moisture levels through moisture sensors.
Moisture levels might be indicated with a color-coded scale of 1 to 10, a percentage, or a decimal ranking.
Even Better: These types of sensors are great tools for beginner gardeners because they are easy to use.
Other Functions of a Soil Moisture Sensor
Some soil moisture detectors provide more features than just measuring water in the soil.
Moisture sensors are available that also measure pH levels, light levels, and possibly temperature.
Moisture sensors also measure pH levels with soil sensors, which measure if the soil is alkaline or acidic. That can inform the user of any additives to use or what plants may thrive.
Soil moisture sensors will also detect other essential nutrients missing from the soil. That will also inform you on additives for the land.
Measuring light levels will also help you pick plants for full sun or shaded areas.
Light level features detect how bright it is in a specific area. In measuring a larger area in moving light, you may require more light level features.
There are moisture meters that also report the temperature, for someone growing a garden or outdoor plants to notify them when the season is about to changes.
That can notify a gardener of the best time to plant vegetables, or spring flowers like tulips or daffodils or when to trim, bushes or trees.
How Are Readings From a Soil Sensor Interpreted?
The typical readings of a soil moisture sensor are expressed in centibars (kPA) ranging from 0 to 100 CB.
Lower values show more saturated soil while high values indicate the normal water holding capacity of soil needing irrigation
For example, 0-10 represents saturated soil, 60-100 is the typical range for water that shows heavy clay soils at field capacity needing supplemental irrigation.
Typically, the proper soil moisture is between 10 and 18 percent.
The displays on the soil moisture sensors can either be manual or digital, relying on the brand and model you go with.
Most recommend finding a meter you can see easily.
How Much Does a Soil Sensor Cost?
Good soil moisture sensors range in price from $100 to $1,000 and would find volumetric sensors to be the most expensive.
Tensiometers will fall on the lower end of the scale and solid state sensors are the least expensive (with some costing around $30).
Some people have made these themselves, but this can require some technical skill to get a good reading.
Some supplies will be needed like probes or electrodes, however.
In Conclusion: In the end, you may spend more on parts to make one that you could purchase a sensor, especially the lower priced ones.
How to Choose the Best Soil Moisture Sensor
The kind of meter you look for will be dependent upon how you intend to use it.
Some meters are well suited for outdoor use and others are best for indoor applications. And there are meters that are made for both outdoor and indoor use.
Overall:
- You are looking for a durable product that also provides detailed information.
- You are looking for one that displays well and works on a variety of soil types.
- Also, getting one that has “smart” features would be great.
If the thermometer is designed for indoor use, the probe will be a shorter probe.
If you are looking for use outdoors, more durability of your sensor will be a necessity and you are looking for a probe that is minimum of 1/4-inch thickness so the probe does not bend.
Stainless steel probes are preferred over plastic probes, and you will obviously be looking for a longer probe than the ones used for indoor use.
Accuracy
Long probes usually have better accuracy, and especially beneficial in areas of deep soil and deep-rooted plants.
Short probes, too, are fairly accurate.
The best method to determine accuracy is to notice the reasons frequently.
The avg attitudes that are stable will show more accuracy than the sensors that are wild all over the place.
Digital or Analog
When purchasing a moisture meter, you will want to decide on analog or digital.
In general, analog devices are less expensive and easier to understand the codes and readings.
They also do not use batteries, and you can easily install them and get to work.
Digital moisture meters will have numerous features, yet they can be a little more expensive.
The added convenience of connected capabilities along with being more accurate makes them more costly.
Again, batteries will also be used for these meters, some may be connected through WiFi!
Some of these smart devices can then be reviewed with your phone and evaluated to monitor your watering needs.
Very useful when you are on a trip or vacation.
Smart Meters
There are smart meters that connect via Bluetooth so you can see the findings in an app on your phone. These devices have a ton of additional features.
You can monitor the growth of a plant, and the device can customize its suggestions for how to assist each plant growth given the conditions.
The type of soil you have may affect your purchase.
For dense soils, such as ones with a lot of clay, you will need a study probe that can penetrate into the harder soils.
Most sensors should work well with indoor potting soil, as it is not as compact.
You may want to test the soil before you spend money on soil moisture devices just to ensure water is the issue. In some cases it may be sodium or other elements.
Plants will not do well if there is another issue such as pH or sodium, so stay focused on this.
Bottom line, understanding your soils would better help you select the appropriate moisture sensor.
Calibration
It will also be helpful to have a meter that can be calibrated for different soils.
With a user-calibrated device, you can easily adjust for each particular use so that you can achieve moisture needs for particular plants.
Calibration makes adjustments for composting or gardening, as well as humidity.
Calibration will therefore increase the accuracy of your device no matter the use.
By calibrating your device you will be able to take specific measurements based on how an area functions.
You may also want a soil moisture sensor that can be used by the whole family.
This is also a great way to teach kids about planting. Some sensors are specifically designed so children can use and read the moisture levels.
These can be inexpensive and battery free.
How Long Do Soil Moisture Sensors Last?
The lifespan of a sensor varies according to the brand and if it is being used indoors or outdoors but sensors generally last three to five years.
Indoor sensors will typically outlast outdoor sensors simply due to the long-term effects of weather and climate on a sensor.
Conclusion
A soil moisture sensor can be very beneficial for gardeners and farmers to better monitor irrigation.
It gives you a better sense for when you should begin irrigating your garden and some meters indicate other information to help make your gardening easier and more successful.
There are many brands, with different features and all are not at all that complex to use, along with very commercial devices used Professional Agriculture.
This user guide for a soil moisture sensor familiarizes you with what you need and how a soil moisture sensor operates, so you can make an informed decision.