Soil Tensiometers

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TS6 Pencil Tensiometer

A tensiometer is a device partially inserted into soil to measure the soil water tension. Soil tension (matric potential) is the suction or force needed to pull water from soil pores (by plants or instruments).  It reflects how tightly water is held in the soil and how much effort (pressure) plant roots need to exert to extract water from the soil.  

How Tensiometers Work
Types of Tensiometers
Tensiometers Compared to Soil Moisture Sensors
Pros & Cons of Tensiometers
TS25 JetFill Tensiometer
TS10 Soil Column Tensiometer

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TS25 JetFill Tensiometers
TS6 Pencil Tensiometers
TS10 Soil Column Tensiometers
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Applications

SectorExample Applications
AgricultureIrrigation scheduling, root zone monitoring, drought mitigation
Used in row crops, orchards, vineyards, greenhouses, and nurseries
EnvironmentalWatershed recharge, landfill liners, wetland studies
ResearchRetention curves, infiltration studies, landslides
ConstructionSlope stability, soil compaction validation
EducationDemonstrations of soil-plant-water relations

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How Tensiometers Work

  • A porous ceramic tip that is inserted into the soil and that allows only water to move in and out.
  • A hollow tube filled with water. 
  • A vacuum gauge or digital sensor mounted at the top.

If the soil is dry, water is drawn out of the tube by the soil matric through the ceramic tip, creating a vacuum that creates a higher pressure that the gauge measures. 

If the soil is moist, less water is drawn out, and the vacuum pressure is lower. 

The gauge reading indicates how hard plants must work to get water from the soil – the higher the pressure (tension) the harder the plant must work.  This measurement correlates with soil water present, but this is not the exact amount or percentage of water present in the soil as measured by a VWC % soil moisture sensor. 

Types of Tensiometers

TypeReadoutAutomationIdeal For
AnalogGauge dialNoBasic irrigation scheduling
DigitalDigital displaySomePrecise monitoring
With Data LoggerDigital + memoryYesResearch, continuous data
Wireless/SmartRemote app/cloudYesSmart farming

Comparison of Tensiometer to Soil Moisture Sensor

The relationship between soil water measurements by tensiometers and soil moisture sensors is crucial in understanding soil water dynamics and is essential to consider both water tension / potential and soil moisture percentage in managing plant hydration. 

In simpler terms, water potential indicates when a plant requires watering, while soil moisture percentage indicates the quantity of water available. 

FeatureTensiometerSoil Moisture Sensor
Measurement TypeSoil water tension (matric potential)Volumetric water content (amount of water per soil volume)
UnitsCentibars (cb) or kilopascals (kPa)Percentage (%) or m³/m³
Operating Range0 to ~85 centibars | 0 to 100 kPa (limited in dry soils)Wide range, including very dry conditions (0 to 100% saturation)
Soil Contact RequiredDirect contact via porous ceramic tipDirect contact via probe or sensor surface
Response TimeSlow to moderate (depends on soil moisture change)Fast and real-time (often instantaneous)
Power RequirementNone (manual), or minimal if digitalRequires power (battery or external source)
MaintenanceHigh (needs refilling, calibration, and cleaning)Low to moderate (depends on sensor type)
DurabilityFragile (ceramic tip can break or clog)Generally more robust and weather-resistant
Data OutputAnalog (gauge) or digital (basic output)Digital with potential for wireless/data logging
Best Suited ForResearch, irrigation scheduling in mid-range moisture soilsAutomated systems, broad-range moisture conditions, smart farming, measurement of soil temperature and electro conductivity
Dry soil accuracyNoYes
Plant-available waterYesNot directly
Understanding the soil type preferredNoYes
High Salinity influence in measurementNoYes
Can measure EC / SalinityNoYes

Pros & Cons of Tensiometers

ProsCons
Measures soil water tension, which directly relates to plant stressLimited to wet to moderately dry soils (typically < 85 centibars or <100 kPa)
Simple and affordable analog models availableNeeds regular maintenance (refilling, cleaning, calibration)
No power required (for analog types)Fragile (ceramic tip can break or clog)
Gives insight into how hard plants must work to access waterSlow response time to rapid soil moisture changes
Suitable for research and fine-tuned irrigationNot suitable for sandy or very dry soils