Guide · soil moisture on the farm
Soil moisture monitoring without the agtech price tag.
Soil moisture changes irrigation decisions more than any other single number on a farm, and you do not need a five-figure agtech package to get it. Here is what the probe actually measures, where to put it, how many you need and what to do with the readings.
Last updated 2 July 2026 · by Rural IoT
The short version, then the detail
Two or three well-placed soil moisture probes, read from the house, tell you when to start watering, when to stop, and when an irrigation run has quietly failed. The probes themselves are cheap. The dashboard and radio network behind them are the real investment, and that platform is shared with every other sensor on the place. New to on-farm sensors altogether? Start with the farm monitoring guide, then come back here.
What the sensor actually measures
A soil moisture probe reads volumetric water content: the percentage of the soil around it that is actually water. A reading of 30% in a loam means the roots are comfortable; at 12% they are working hard for every drop. What counts as wet or dry shifts with soil type, sand drains fast and clay hangs on, so the raw number matters less than where it sits between your soil's full point and its stress point.
The feel test, grab a handful and squeeze, only tells you about the top few centimetres, on the day you drove out, in the one spot you dug. A probe reads the root zone every hour, logs every reading and never gets bored of checking. The decision moves from "feels a bit dry" to a number you can act on.
Capacitive or resistive: buy the one that lasts
Cheap probes come in two types. Resistive probes pass a small current through the soil between two exposed metal legs, and the soil eats them: corrosion drifts the reading within months and then kills the probe outright. Capacitive probes sense the water through a sealed, coated board with no exposed metal in the ground. For anything that lives in a paddock, capacitive is the only type worth fitting.
Where to put the probes
Put the probe where the roots are, not where the ute parks. Two things decide it: depth and location.
Depth first. Match the probe to the root zone of what you are growing. Pasture pulls most of its water from the top 10 to 30 centimetres, so one probe in that band does the job. Vines, trees and deeper-rooted crops want a probe around 30 centimetres and another near 60, to show whether water is reaching the deep roots or drifting straight past them.
Location second. Pick spots that represent the country you are actually making decisions about: mid-paddock, typical soil, typical slope. Not the corner by the gateway, not the compacted ground near the trough, not the hollow that stays wet for a week after rain. One honest probe in a representative spot beats three convenient ones.
Two depths in the one hole also show the run working: the shallow probe should jump first and the deep one follow a few hours later. If the deep one keeps climbing, you are pushing water past the roots and paying to drain your own paddock.
How many you actually need
Fewer than the brochure says. Start with two or three probes in the zones that drive decisions: the block you irrigate first, your heaviest soil and your lightest. If two probes always agree, one of them is telling you nothing new.
A grid of fifty probes generates a wall of data and no better decisions. Add a probe when a specific call would have gone differently with a number from that spot, and not before. One more probe is just one more line on the same dashboard.
Getting the reading back to the house
The probe is the easy half. The useful half is the reading arriving at the house without anyone driving to fetch it. Farm-grade sensor nodes send their readings over long-range, low-power radio back to a receiver at the house or shed. The link carries for kilometres and needs no mobile signal at the probe, which matters, because the paddock that needs the probe is usually the one with no bars.
Power is solved the same way. A small solar panel and a battery at the node run it for years. No trench, no mains, no electrician for the sensor itself. Fit it, watch it report in, walk away.
Three decisions the numbers change
The data is only worth having if it changes what you do. Three places it does.
Irrigate on numbers, not the calendar
Set a refill point for each zone and start the pump when the root zone reaches it, not because it is Tuesday. Stop when the profile is full. A schedule wastes water in a mild week and stresses the crop in a hot one; the probe ends both.
Catch the failed run
A blocked line, a tripped pump or a stuck valve looks like nothing from the house. On the chart it is a flat line where a rise should be. You find out the same morning, not when the crop shows it weeks later.
Watch the drying curve
The slope of the drop tells you how many days you have before a zone hits stress. That turns irrigation from reaction into planning, and season on season the curves show you what each paddock really does.
The honest cost picture
Here is the part the glossy agtech brochures skip. A soil moisture node, probe, radio and solar power included, is a tens-to-low-hundreds of dollars item, not a thousands one. The real money is the platform behind it: the receiver, the dashboard, the alerts and the logged history.
And the platform is shared. The same receiver and dashboard that carry your soil probes also carry gate sensors, tank levels, pump pressure and frost alarms. Spread across everything it watches, it earns its keep fast, and every sensor you add after it is the cheap part. We cover that economics properly in one platform, many uses.
One more position, and we hold it firmly: own the gear. No monthly subscription to read your own paddock, no account that bricks the sensors if a company folds or changes its pricing. Buy it once, own the data, run it for years.
When the big agtech systems are worth it
Fair is fair: the five-figure systems exist for a reason. If you are running variable-rate irrigation on centre pivots across hundreds of hectares of high-value crop, with an agronomist reading the data and the water bill to match, the integrated platforms earn their price. Buy one and use all of it.
Most farms are not doing that. They need to know when to start the pump, when to stop it and when a run has failed. Two or three good probes and a dashboard answer all three, for a fraction of the money.
Questions people ask
Capacitive or resistive soil moisture sensor, which should I buy?
Capacitive, every time, for anything left in the ground. Resistive probes pass a current through exposed metal legs and the soil corrodes them within months, taking the reading with them. Capacitive probes are sealed, drift far less and last for years.
How many soil moisture sensors does a farm actually need?
Start with two or three in the zones that drive decisions: the block you irrigate first, and your heaviest and lightest soils. Add more only when a specific call would have gone differently with a reading from that spot.
What depth should soil moisture probes be installed at?
Match the root zone of the crop. Pasture draws most of its water from the top 10 to 30 centimetres. Vines, trees and deeper-rooted crops want a probe around 30 centimetres and another near 60, so you can see whether water is reaching the deep roots or draining past them.
When should I irrigate based on soil moisture?
Set a refill point for each zone, the reading where the crop starts working too hard for water, and start the pump when the root zone reaches it. Stop when the profile is back to full. Irrigating on the numbers instead of the calendar saves water in a mild week and saves the crop in a hot one.
How does the reading get from the paddock to the house?
Over long-range, low-power radio to a receiver at the house or shed. The link carries for kilometres and needs no mobile signal at the probe. The sensor node runs on a small solar panel and battery, so there is no trenching, no mains power and no electrician needed for the sensor itself.
Do I need a subscription to see my soil moisture data?
No. We set up systems you own outright: the probes, the receiver, the dashboard and every logged reading. There is no monthly fee to look at your own paddock, and the gear keeps working whether or not any company does.
Know when to irrigate before the crop tells you.
Tell us what you grow and where the water decisions get made. We will come back with a probe plan and a price, no pressure, no jargon.
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