How much water, and when
A moisture sensor says how wet it is now. The question is whether to irrigate, how much, and whether it fits in one application. FairGrow keeps a soil water balance per FAO-56 for that, with your readings, your weather and the slope of your plot.
Moisture is a balance, not a snapshot
A moisture sensor tells you how wet it is right now. That is not the same as knowing whether to irrigate. FairGrow keeps a soil water balance per FAO-56: what goes in through rain and applications, what leaves through evaporation, and how much fits in the root zone. What you see on your screen is that balance, fed by your own readings and the weather at your location.
How much you may give depends on your plot
Knowing that you have to water is half of it. The other half is how fast you may give it. Give it faster than the soil takes it up and it runs off across the surface, and you have a wet ditch rather than a wet root zone. FairGrow works out the maximum application rate from the infiltration guide values: the finer the soil and the steeper the plot, the sooner water runs off.
How many millimetres per hour fit in
From the soil texture and the slope of your plot follows how fast water can enter it. That rate, together with the length of an application, sets how many millimetres fit in one go.
Two applications rather than one long one
If the amount does not fit in one application, the advice says in how many it does fit. An application runs for at most two hours by default, because after that the soil no longer takes it up at the same pace anyway.
Which corner stays wet longest
The height difference across your plot comes from the Copernicus elevation model. From it follows which corner stays wet longest and which dries out first, and above three per cent slope the aspect counts as well.
What happens when something is off
An irrigation system that keeps pumping because a sensor has failed does more damage than a system that does nothing at all. The locks below sit in the core and cannot be worked around with a setting.
The master switch is off
Switching is off by default. A zone sits in observe mode, and only when you deliberately set it to live and turn the master switch on does anything happen in the field. Computing and showing works without a valve ever opening.
Pulses, not an open tap
A pump gets a pulse and stops itself, rather than an “on” instruction that stays standing. If the connection drops at the wrong moment, the system closes by itself instead of running on.
Emergency stop on rain
If it starts raining while an application is running, that application stops. And if more than a couple of millimetres of rain are forecast, the advice postpones the application rather than scheduling it anyway.
An old reading is not a reading
If the last moisture reading is too old, nothing is pumped. That is deliberately the safe side: better to miss an application than to irrigate on yesterday’s number while 20 millimetres fell overnight.
Daily ceiling and rest period
Each zone has a maximum per day and a minimum time between two applications. So a faulty sensor or an unlucky rule can never put a plot under water.
Honest when something is missing
If data is missing, the screen says so. It does not quietly show advice built on half the picture, because that is the kind of fault you only see once the crop tells you.
Open model, visible assumptions
The soil water balance follows FAO-56, the standard also used in the European OpenAgri work. The starting values sit in the code rather than in a black box: field capacity, wilting point, the depletion limit at half, and an effective root zone of thirty centimetres.
- Above sixty per cent of field capacity the system advises against irrigating
- Below forty per cent it always advises to irrigate, even if the weather still looks reasonable
- More than two millimetres of rain in the forecast means postponing
- The run-off deduction on forecast rain is switched off, because a sensor already measures that and you would otherwise count it twice
What this is not
This is not a decision taken for you. The system computes, shows and warns; whether a valve opens is up to you, per zone, behind a master switch that is off by default. That order is deliberate: first watch along for a season to see whether the advice matches what you would have done yourself, and only then consider handing it over.
The starting values are FAO-56 defaults. They are a reasonable point of departure and not a measurement of your soil. Anyone who wants to know their field capacity precisely should have it determined; what is here is good enough to see the moment coming, not to base a trial plot on.
The moisture reading itself is a subject of its own. How often a soil moisture sensor ought to measure, and why more often is not better, is on that page. The weather it computes with comes from NASA POWER and the satellite imagery from Copernicus.
What growers ask us
Will FairGrow drive my pump by itself?
Only if you explicitly turn that on. By default every zone sits in observe mode: it computes and shows, and nothing happens in the field. Switching takes two deliberate actions, the zone to live and the master switch on.
Do I need a soil moisture sensor?
For a full balance, yes. Without a sensor you can estimate from the weather, but then you miss exactly what your soil actually holds. With a sensor the balance is corrected at every reading instead of running on assumptions.
Why does the system advise two applications instead of one?
Because your soil does not take water up faster than it can. Above that rate it runs off across the surface. The finer the soil and the steeper the plot, the sooner that happens, and then two shorter applications are the way to get the same millimetres in after all.
What if my sensor fails?
Then nothing is pumped. A reading that is too old counts as no reading, and the system takes the safe side. You see that stated on your screen, so you know it is quiet because something is missing and not because nothing is needed.
Does this work in a glasshouse?
Yes, with the caveat that rain and evaporation behave differently indoors. The balance itself is the same; what changes is how much the weather outside still says about what happens inside.
Watch along for a season first
Put your zone in observe mode and lay the advice next to what you would have done yourself. If it matches, you can consider handing it over. If it does not, you know that without a drop too much or too little having been given.
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