A soil moisture monitoring system is only as useful as the question it answers. Some sensors tell you how much water is in the soil. Soil tension sensors tell you how hard the plant has to work to get it.
If you are comparing a soil tension sensor with volumetric probes from brands such as CropX or SoilSense, start there. They are not interchangeable readings with different stickers.
A short definition of soil tension
Soil tension (also called soil matric potential) is the effort required to pull water out of the soil. Wet soil holds water loosely, so tension is low. Dry soil holds water tightly, so tension is high. Readings are usually reported in centibars (cb) or kilopascals (kPa). Zero is wet. Higher numbers are drier.
That is the number roots actually fight. It is why tension is useful for irrigation timing across mixed soils, where the same volumetric percentage can mean “plenty” in sand and “stress” in clay.
What volumetric soil moisture sensors measure
Volumetric sensors report volumetric water content (VWC): the percent of a soil volume that is water.
CropX’s published soil-sensor materials describe VWC via amplitude domain reflectometry, plus temperature and electrical conductivity, feeding an agronomic software platform.
SoilSense’s own technology overview describes TDT (time domain transmissometry) probes that estimate VWC from the soil’s dielectric properties, and contrasts that approach with Watermark-style tension sensors and tensiometers.
VWC is a real measurement. It becomes an irrigation decision only after you know that soil’s field capacity and wilting point. Without that context, 25% moisture is not a start/stop rule.
What a soil tension sensor measures
Granular-matrix sensors (Irrometer Watermark is the common field name for this category) and tensiometers measure tension, not percent water.
Mississippi State University Extension’s Irrometer Watermark Series treats Watermark data as a gauge of the soil-water “fuel tank.” Centibars are low when wet and high when dry. The sensor does not need a separate sand-vs-clay translation table to tell you the plant is working harder.
Tradeoffs are real. Volumetric TDT/TDR probes are often more precise and faster. Tension sensors are usually cheaper per point, more directly tied to irrigation triggers, and easier to explain in the field. Clay and salinity can affect some granular-matrix readings. Tensiometers need maintenance and have a limited dry-end range. No sensor replaces walking the crop.
AgriLynk’s public product copy describes soil tension sensors in the root zone, typically at three depths on starter systems. Confirm the current sensor hardware on a quote. Do not assume every AgriLynk station is a Watermark 200SS unless the invoice says so.
When-to-irrigate rule of thumb
Rule of thumb: Start irrigation when the weighted tension in the active root zone approaches the crop’s stress threshold, and stop when the wetting front reaches the depth you intend to fill. Tension rising at shallow and mid-root, with the deep sensor still quiet, usually means the crop is drinking the profile you filled. A deep sensor that never moves often means roots are not there yet, or irrigation is not reaching that depth. A deep sensor that stays wet while the crop looks stressed is not a “add more hours” signal. Look at salinity, roots, and whether water is sitting below the active zone.
Mississippi State Extension, writing for Watermark sensors in mid-South row crops, reports that yield-reducing stress tends to show up when the weighted-average reading exceeds about 100 centibars, and it recommends starting sooner when the irrigation system takes several days to cycle (for example, about 76 cb on a four-day cycle). That is a researched row-crop neighborhood, not a universal almond, grape, or nursery number.
Wine grapes, almonds, and other perennial crops are often managed to different plant-water targets, including pressure-chamber baselines and deficit strategies. Set the AgriLynk threshold with your CCA for that block and that season. The rule does not change: irrigate from tension in the active root zone, not from a wet circle on the surface.
Which sensor fits which farm question
| Question | Tension / Watermark-style | Volumetric (CropX, SoilSense, similar) |
|---|---|---|
| How hard are roots pulling right now? | Direct | Indirect, after soil calibration |
| How much water is stored in this layer? | Indirect | Direct (VWC) |
| Same trigger across sand and clay? | More transferable | Needs soil-specific set points |
| Also want EC / salinity profile? | Not the strength of a basic tension point | Often included (CropX EC; many TDR/TDT probes) |
| Platform with agronomic models and satellite layers | Not AgriLynk’s pitch | CropX-style agronomy suites |
| Start small, then add remote valves | AgriLynk Monitor, then Control | Usually a separate control stack |
Use both if the farm will actually look at both. Do not buy two platforms to delay a decision.
How AgriLynk fits
AgriLynk is a soil-tension-first monitoring system that can add remote valve control, threshold automation, and well or tank visibility. It is not a volumetric probe company and not a full agronomy suite.
Starter path on the current site:
- How AgriLynk works
- 2026 pricing (Monitor, Control, Autonomous, Enterprise)
- Remote irrigation automation if the next step is valves, not more sensors
You still decide when to irrigate. The soil tension sensor is there so that decision is based on the root zone, not the calendar.
Sources
- Mississippi State University Extension, Publication 3541, Irrometer Watermark Series: Irrigation Triggers (POD-01-24): extension.msstate.edu/publications/irrometer-watermark-series-irrigation-triggers
- CropX soil sensor / Apex product literature (VWC via ADR; EC and temperature)
- SoilSense, Soil moisture sensor technologies: An overview (TDT vs Watermark vs tensiometer vs capacitance)
