Irrometer Soil Moisture Instruments
Tensiometers, WATERMARK sensors, meters, monitors and the parts that keep them working. Irrometer has built soil water management instruments since 1951, and we carry the line in our online store with the rest available to order.
Tell us your soil, your crop and how deep the roots run, and we will tell you which instrument reads it.
Measures tension, not guesswork
A tensiometer reads how hard roots must work to pull water from the soil, in centibars, which is what decides when to irrigate.
Two technologies
Tensiometers for the wet end of the range, WATERMARK granular matrix sensors for drier soils and remote logging.
Parts and service kits
Replaceable ceramic tips, gauges, stoppers, fluid and hand vacuum pumps. One service kit serves any number of instruments.
Shipped direct from Irrometer
Orders ship from the factory in Riverside, California, so you get current production rather than shelf stock.
Start here: which instrument do you need?
Choose by the soil you are irrigating and the range you manage in.
| If you are irrigating… | Look at | Why |
|---|---|---|
| Most field soils, orchards and row crops | SR tensiometer | The 0–100 cb dial covers the range these soils are irrigated in |
| Coarse sands, rocky hillsides or Florida sand | LT tensiometer | A 0–40 cb dial spreads the scale where these soils actually operate |
| Greenhouse benches, containers and potting media | MLT tensiometer | Short body and 0–40 cb dial sized for pots and trays |
| Dry-farmed ground, deficit irrigation or readings past 100 cb | WATERMARK sensor | Reads well beyond the range a tensiometer can hold |
| Sites you cannot walk every morning | WATERMARK with a monitor | Logs and reports readings without anyone standing at the gauge |
| Starting a valve or controller from soil moisture | AVS switch or RSU transducer | Turns a tension reading into a switch closure or an analog signal |
Not sure which end of the range your soil sits in? Send us the soil type and crop and we will tell you.
What the readings mean
A tensiometer reads 0 in saturated soil, and the number climbs as the soil dries. These are Irrometer's own general guidelines.
Centibars (cb) and kilopascals (kPa) are the same number on these instruments. Your local cooperative extension service or an agronomist can set thresholds for your specific crop and soil.
The instruments
SR Tensiometer
The model most growers use. A 2.5 in. stainless gauge on a sealed plastic body with a replaceable threaded ceramic tip, available in lengths from 6 in. to 48 in. so you can read at the depth the roots are working.
- Dial range 0–100 cb / kPa
- Gauge 2.5 in. stainless, IP67
- Accuracy 3-2-3% of span, ASME B40.1 Grade B
- Operating range 33–150°F (0.5–65°C)
- Tip Replaceable threaded ceramic
LT Tensiometer
Same instrument as the SR with a 0–40 cb dial, so the scale is spread across the range that coarse soils actually operate in. Built for soils where readings above 30 cb are not expected: avocados on rocky hillsides, citrus in sand, greenhouse media.
- Dial range 0–40 cb / kPa
- Gauge 2.5 in. stainless, IP67
- Best for Sands, rocky and coarse soils
- Tip Replaceable threaded ceramic
MLT Tensiometer
A short instrument for containers, greenhouse benches and propagation. It is serviced with a syringe rather than the hand vacuum pump, and the tip and tube replace as one assembly.
- Dial range 0–40 cb / kPa
- Gauge 1.5 in.
- Accuracy ±5% (Grade D)
- Overall length 6.75 in.
WATERMARK Sensor
A solid-state sensor with no water reservoir and nothing to refill, buried and left in place. It reads across a far wider range than a tensiometer, which makes it the instrument for drier soils and for anything logged or read remotely.
- Reads Well past 100 cb
- Maintenance None in season
- Read with Handheld meter or monitor
- Standard lead 5 ft (longer available)
Outputs and automation
Every one of these turns a soil moisture reading into something a controller, a datalogger or a phone can act on.
- AVS switch A vacuum switch on the tensiometer that closes as the soil dries past a set point. Set range 5–85 cb, adjustable by hand in the field, SPST normally open, 24 VAC 10 A max.
- RSU-V transducer Converts the tensiometer reading to a voltage output for a datalogger or controller.
- RSU-C transducer The same in a 4–20 mA current loop, for long cable runs and industrial inputs.
- PPS pressure switch A preset 5 psi pressure switch for irrigation line sensing.
- Handheld meter Reads WATERMARK sensors directly in the field, one sensor at a time.
- 900M monitor Reads and logs a group of WATERMARK sensors at the site.
- IC-10 IRROcloud Sends readings to Irrometer's IRROcloud service so you can see them without driving out.
- Soil temperature sensor Adds soil temperature alongside moisture on monitored sites.
The AVS is factory-set to 5 cb if you do not give a set point with the order, and can be adjusted on site afterwards.
Shop by category
Everything below is in our online store with current pricing.
Service kits
The 1001 kit is a hand vacuum pump, chart forms, fluid and the reference booklet. The 1002 adds a test gauge on the pump so you can check the instrument's own gauge. One kit services any number of instruments.
Replacement parts
Ceramic tips, gauges, caps, stoppers, O-rings, suction line and tubing, plus the vinyl caps and fittings used in multi-depth pipe assemblies.
Not listed?
Irrometer's catalog runs wider than our store. Send the part number or describe what you need and we will quote price and lead time.
Getting the placement right
A tensiometer only tells you about the soil it is sitting in, so where you put it decides whether the reading is worth anything.
| Situation | Where the instrument goes |
|---|---|
| Trees | At the drip line, in the wetted area and the active root zone |
| Row crops | In the row, not between rows |
| Drip irrigation | 12–18 in. from the emitter |
| Sprinklers | 24–36 in. from the sprinkler |
| Flood or furrow | Two-thirds of the way down the run |
| Roots deeper than 18 in. | Two instruments: shallow at 25% of root depth, deep at 75% |
Install into wet soil
Install right after an irrigation. Make the hole with the installing tool or a 1/2 in. steel pipe, and leave about 1 in. between the gauge and the ground.
Read in the morning
Morning readings are the most accurate, and reading at the same time each day is what makes the trend meaningful.
Check the tip once a year
Fill the instrument and hang it for 24 hours with the cap off. If less than 1 in. has drained, the tip needs replacing.
Frequently asked questions
What is the difference between a tensiometer and a WATERMARK sensor?
A tensiometer is a sealed, water-filled tube with a ceramic tip and a vacuum gauge; it reads soil water tension directly and works at the wet end of the range, roughly 0 to 100 cb. A WATERMARK sensor is a solid-state granular matrix sensor with no water in it, buried and left alone, and it reads well past the range a tensiometer can hold. Tensiometers are the better choice where irrigation happens in the wet range; WATERMARK is the choice for drier soils, for deficit irrigation, and for anything you want logged or read remotely.
What reading means it is time to irrigate?
It depends on the soil. Irrometer's general guidelines are that 0–10 cb is saturated, 10–30 cb is adequately wet for most soils though coarse sands and potting media are already drying, 30–60 cb is the usual irrigation range for most soils, and 60–100 cb is the usual range for heavy clay. Above 100 cb the soil is very dry and should be managed with a WATERMARK sensor. Your extension service or agronomist can narrow these to your crop.
Should I buy the SR or the LT?
The SR, with its 0–100 cb dial, suits most field soils and is what most growers use. The LT reads 0–40 cb, which spreads the scale across the range coarse soils actually operate in, so it is the better instrument for sands, rocky hillsides and greenhouse media where you never expect to see 30 cb. If your soil drains fast and you irrigate often, ask us about the LT.
What length should I order?
Match the depth to where the roots are working, not to the plant. Tensiometers are available from 6 in. to 48 in. If the roots go deeper than 18 in., use two instruments at the same spot: a shallow one at about 25% of root depth and a deep one at about 75%, so you can see water moving through the profile.
How much maintenance does a tensiometer need?
They need refilling with Irrometer fluid when the reservoir drops, which is routine during the season, and a service kit with a hand vacuum pump to pull the air out after filling. One kit services any number of instruments. Check the ceramic tip once a year by filling the instrument and hanging it for 24 hours with the cap off; if less than an inch has drained, replace the tip.
What happens in freezing weather?
Freezing damages the gauge. Where frost is light and uncommon, an insulated box over the instrument can protect it. In colder places, remove the gauge or the whole instrument for the winter.
Why does my long tensiometer not read zero in saturated soil?
That is the weight of the water column inside the instrument, not a fault. A capped instrument reads roughly 1 cb for every 4 in. of length, so a 12 in. instrument sits near 3 cb and a 24 in. instrument near 6 cb when the soil is saturated. Treat that as the zero point for that instrument.
Can a tensiometer start my irrigation automatically?
Yes. The AVS vacuum switch mounts on the instrument and closes as the soil dries past the set point you choose, which can drive a valve or a controller input. It is set between 5 and 85 cb and is adjustable by hand in the field. If you need a continuous signal rather than a switch, the RSU-V gives a voltage output and the RSU-C a 4–20 mA current loop.
Can you supply Irrometer items that are not in your online store?
Yes. Our store carries the models we sell most, and Irrometer's catalog runs wider than that. Send us the Irrometer part number, or describe what you are trying to measure, and we will quote price and lead time.
Do you ship outside the United States?
Yes. Exporting is what Jealco has done since 1950. Send us the destination country and the incoterms you work on and we will quote the goods and the freight together.
IRROMETER, WATERMARK and IRROcloud are trademarks of their owner. Specifications and guidelines on this page are from Irrometer's published literature.
Not sure which instrument reads your soil?
Send us your soil type, the crop, how you irrigate and roughly how deep the roots run. We will tell you which instrument fits, at what length, and what it costs delivered.