How a tensiometer tells you when to water

A tensiometer is a sealed, water-filled tube with a porous ceramic tip buried in the root zone and a vacuum gauge on top. As the soil dries it pulls water out through the ceramic, creating suction in the tube that the gauge reads in centibars. That suction is the same pull roots must overcome to drink, so a rising reading means it is getting harder for the crop to get water.

Controls

Labels

Animation speed

Gauge reading

Soil texture

Step through it

Placed in the root zoneThe ceramic tip is buried where most active roots are, often a third to half of the way down the root zone. Many growers add a second, deeper unit.
Soil pulls on the waterDrying soil sucks water out through the fine pores of the ceramic. The sealed tube cannot let air in, so a vacuum builds.
Reading the gaugeThe gauge reads that suction in centibars, which equal kilopascals. Near 0 is saturated; around 10 to 20 is field capacity in many soils.
Sand dries fastSandy soil holds little water, so its usable water is mostly gone at a low reading. Irrigate sand sooner on the gauge than clay.
Clay holds onClay grips water tightly and holds more of it, so growers usually wait for a higher reading before watering.

Tension versus allowed depletion

Irrigators plan around management allowed depletion: the share of plant-available water they let the crop use before refilling, commonly about half. A tensiometer does not measure water content directly, so each soil needs its own link between reading and depletion.

This model uses a simplified straight-line link that puts 0 percent used at 10 cb and 50 percent used at a trigger of 25 cb for sand, 45 cb for loam and 60 cb for clay. Real soils follow curved moisture release curves, and extension guides publish crop- and soil-specific trigger readings. Refill depth assumes 70, 170 and 180 mm of available water per meter of soil.

Try it: set the reading to 35 cb and switch between Sandy, Loam and Clay. Sand reads 'Irrigate now' with over 80 percent of its small water store already used, while loam and clay still say 'Moist'.

Limits of the tool

Above about 80 cb air leaks in through the ceramic and the tensiometer stops working, so it suits crops and soils kept fairly moist: vegetables, orchards, berries and turf. It needs good contact with the soil and occasional refilling, and it reads one spot, so placement matters.

Where Avid uses this

Soil moisture sensing like this is one of the inputs precision irrigation tools, such as Avid's VerdantaIQ, use to decide when and how much to water.

Sources

Irrigating Your Orchard: Water Monitoring with a Tensiometer (FS1306)Rutgers New Jersey Agricultural Experiment Station
Using Tensiometers for Vegetable Irrigation Scheduling in Miami-Dade CountyUniversity of Florida IFAS Extension
Measuring Soil Water Potential for Water Management in Agriculture: A ReviewSustainability (MDPI, open access)

How to cite this model

Avid Solutions International. (2026, November 11). How a tensiometer tells you when to water [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/tensiometer

Last updated November 11, 2026

Keep exploring

Water & IrrigationInside a centrifugal irrigation pump Water & IrrigationHow an Archimedes screw lifts water Water & IrrigationHow a center pivot waters a circle Water & IrrigationHow drip irrigation feeds each plant