Capacitive probe or tensiometer: which to choose for irrigation management?

You are standing at the edge of the plot, the surface is dry, but you have no idea what is happening at 40 cm, where the roots are working. Start the irrigation cycle now or wait three days? Two families of tools answer that question: the tensiometer and the capacitive probe. They do not measure the same thing — and that is where everything plays out.

The tensiometer: measuring the plant’s effort

A tensiometer is a water-filled tube, closed by a porous ceramic tip, buried at root depth. As the soil dries, it draws water out of the tube through the ceramic: the vacuum created is read in centibars (cbar). The higher the value, the harder the plant has to work to extract water.

That is its great quality: it measures tension, in other words directly the effort the plant is making. A threshold in centibars transfers from one soil type to another more easily than a moisture percentage.

Its limits are well known to anyone who has used one:

• Regular maintenance: bleeding it, topping up the water, checking the ceramic tip has not lost contact. A tensiometer that has lost its prime shows a false reading without warning.
• Limited measuring range: beyond roughly 80 to 100 cbar, the water column breaks. In very dry soil — precisely the critical moment — the instrument no longer measures anything.
• Frost: it has to be removed or drained before winter.
• One reading = one depth: to monitor two depths, you need two instruments, twice the maintenance, two readings.
• Often a manual reading: dial versions require a trip to the plot. Connected versions exist, generally with a subscription.

The capacitive probe: measuring the water actually there

A capacitive probe measures the dielectric permittivity of the soil — in plain terms, it derives the volumetric water percentage: how many litres of water in 100 litres of soil, at each equipped depth. No liquid, no porous tip, no priming: a tube buried once, measuring continuously.

Its strengths for irrigation management:

• Several depths on a single tube: 2, 3 or 4 depths depending on the model. You see the surface and the deep reserve on the same curve.
• No in-season maintenance: no bleeding, no water top-up, no dropout in dry soil. The measurement stays valid from saturated soil to very dry soil.
• Continuous, remote measurement: with a connected probe, values come in several times a day and the history builds itself.

Its limit: the volumetric percentage depends on soil texture. 18% moisture is comfortable in sand and already tight in clay. So you need a calibration per soil type — FURGO probes come pre-calibrated for 3 soil types, you select yours in the interface — and a first season of observation to set your thresholds.

Head to head, by use case

Criterion	Tensiometer	Capacitive probe
Quantity measured	Tension (plant effort, cbar)	Volumetric moisture (% water)
Depths	1 per instrument	2 to 4 depths on one tube
Very dry soil	Breaks down beyond ~80-100 cbar	Measurement stays valid
Maintenance	Bleeding, re-priming, winter removal	None in season
Reading	On site (or connected with subscription)	Remote, continuous
History	Manual, unless connected version	Automatic
Thresholds	Transferable between soils	To be set per texture

In practice, by crop:

• Vineyard: roots go deep, and what matters is the deep reserve at the end of summer. A single tensiometer at 30 cm misses it; you would need two or three, all maintained. A 60 cm probe with 2 depths covers the profile with a single tube.
• Orchard: fruit size is decided over short windows. A remote alert when the threshold is crossed beats a weekly reading round.
• Market gardening: shallow roots, frequent irrigation. The tensiometer has historically been at home here (soil rarely very dry, single depth) — this is where it remains fully relevant. A single-depth capacitive probe does the same job with no maintenance, plus the history.

Why multi-depth changes the reading

A single measurement says “the soil is at X%”. Two to four depths tell a story: after an irrigation cycle or a rain, you watch the wetting front move down from one depth to the next. If the deep layer does not move, the water stayed at the surface — the cycle was too short, or too fast for that soil. It is often the first surprise for users, and it changes irrigation run times from the very first season.

Multi-depth also reveals the actual rooting depth: the depth where moisture drops every day in summer is the one where the roots are drawing. You then place your thresholds where they matter, not where the catalogue decided.

So, which should you choose?

The tensiometer remains a good tool if you are in market gardening or shallow-rooted crops, if you walk the plot every day anyway, and if the maintenance does not put you off. It is simple, proven, and centibar thresholds are well documented.

The capacitive probe takes the lead as soon as you want history, several depths, a reliable measurement in dry soil, or alerts without going on site. At FURGO, the range runs from €423.50 excl. VAT (1 depth) to €993.40 excl. VAT (60 cm, 4 depths), SIM and platform included, no subscription: the probe calls you when your threshold is crossed. Model details are on the no-subscription capacitive probe page.

Frequently asked questions

Can tensiometer centibars be converted into a moisture percentage?

Not directly: the relationship between tension and volumetric moisture depends on soil texture (the retention curve). In practice, if you switch from a tensiometer to a capacitive probe, keep your agronomic reference points (crop condition, trigger dates) and set your new thresholds over a first season of observation.

Does a capacitive probe need to be calibrated on my plot?

FURGO probes come pre-calibrated for 3 soil types; you select yours in the interface, with nothing to handle. For irrigation management, what counts is the relative movement of the curve and your thresholds, more than the absolute value to the nearest decimal.

How many depths should I choose for my crop?

Identify the rooting depth (a quick auger hole is enough). For shallow situations — market gardening, young plantings — one depth is enough. For vines and orchards on medium to deep soil, 2 depths (40 or 60 cm) separate the surface from the reserve. The 3- and 4-depth versions profile the whole soil, useful in heterogeneous soils or for watching the wetting front in detail.