Fertigation turns a basic irrigation block into a dosing system, and every component between the stock tank and the emitter becomes a potential failure point. Most field problems are not mysterious: they trace back to a small set of causes — air in a suction line, a tired injector diaphragm, a filter that is cleaned too late, or two fertilizers that should never have met in the same tank. The troubleshooting steps below are organised by symptom, so a grower, farm manager or procurement buyer can narrow down the cause quickly and decide whether the fix is a spare part, a procedural change, or a system upgrade.
Injection and Dosing Faults: When EC and pH Do Not Match the Recipe
The first sign of trouble is usually a reading: electrical conductivity lower or higher than the recipe, pH drifting away from target, or a stock tank that empties more slowly than the injection schedule predicts. Before touching the recipe, verify that the equipment is actually delivering what it claims.
Calibrating the injector against a measured volume
The simplest reliable test is a drawdown check. Mark the stock tank level, run the system at normal operating pressure for a fixed period, measure the volume drawn, and compare it with the rated output for that setting. A worn diaphragm, a stretched seal or a partially seized metering pump usually shows up as a slow, consistent shortfall rather than a sudden failure. On proportional pumps, confirm the adjustment ratio is locked where it was set; vibration and hand adjustment during maintenance are frequent causes of drift. If a controller doses against a water meter, check that the meter or pulse emitter is not fouled, because a sluggish meter makes the controller under-dose while the display still looks correct.
Suction-side air and venturi limitations
Venturi injectors depend on a pressure differential across the unit. When the differential falls below the manufacturer’s requirement, suction becomes weak or intermittent. Typical causes include a filter upstream that is loading up and raising back pressure, a throttled valve downstream, or a main line that is simply too small for the combined irrigation and injection flow. Air leaks are just as common and often overlooked: loose clamps, a cracked suction hose, a foot strainer sitting partly above the liquid line, or crystallised fertiliser sealing part of the mesh. Air in the suction line produces a pulsing injector and dosing that swings between rich and lean, which is far harder to spot than a complete stoppage.
Injection point and protection
Confirm where the fertiliser enters the system relative to the filter and the non-return valves. An injection point that lets concentrated solution sit in a dead leg will corrode fittings and create a slug of strong nutrient when the zone next starts. Check that a functioning check valve and suitable backflow protection are in place, and that the injection point is arranged so that any precipitate that does form is captured by filtration rather than carried into the laterals.
Clogged Emitters, Pressure Loss and Uneven Distribution in the Field
Distribution problems rarely announce themselves. They appear as a weak crop row, dry patches at the far end of a block, or a lateral that wets a narrower strip than its neighbours. Walk the block and read the symptoms in sequence, from the headworks outward.
Reading the symptoms along the lateral
If the first emitters run well and the far end of the lateral is weak, the issue is usually pressure loss from undersized sub-mains, excessive lateral length, elevation change or partially closed valves. If flow is low along the whole lateral, suspect a clogged filter or a strainer that has not been cleaned. If some emitters run and others do not, examine the pressure-compensating drippers and drip tape outlets: calcium carbonate, iron deposits, biofilm and algae all narrow the flow path, and a compensating dripper will keep a nominal flow rate until its compensation range is exhausted and then fail suddenly. Dig out a sample emitter, cut a section of tape and inspect it — physical evidence beats guesswork. When replacing laterals, drippers or filtration components, sourcing from an irrigation equipment manufacturer that publishes flow-rate tolerances and filtration requirements makes future diagnosis considerably easier.
Filtration performance and flushing discipline
Filter condition sets the ceiling for everything downstream. A screen or disc filter should be cleaned on a pressure differential, not on a calendar, and the differential gauge itself should be checked because a blocked gauge reads zero while the element loads. Sand media filters need correct backwash flow and duration; weak backwash leaves media channelled and filtration ineffective. At the end of laterals, ensure flush valves are opened periodically at full velocity so that settled sediment and precipitates are pushed out rather than merely stirred. Flush manifolds that are too small, or flush cycles run at low pressure, allow material to accumulate quietly until emitters begin to plug.
Chemical Compatibility, Precipitation and Maintenance Failures
Many “equipment” faults are actually chemistry faults. Calcium-based fertilisers and phosphate or sulphate products will form insoluble precipitates when mixed at high concentration in the same tank, and the resulting cloudiness ends up as scale inside injectors, filters and drip tape. Water chemistry matters too: hard water with high bicarbonate raises pH and encourages carbonate scaling, particularly where the solution warms in the tank.
Mixing order and dilution practice
Follow a consistent filling order — water first, then the least soluble product with agitation, then the next — and never combine calcium and phosphate or sulphate concentrates directly. Use separate stock tanks and separate injection points where the recipe requires both. Keep stock solutions at working dilution rather than near-saturation, and test small jar samples of any new combination before committing a full tank. Record tank temperature and mixing times during hot weather, because warm water reduces solubility and crystallisation can begin in lines overnight.
Safety, backflow and scheduled maintenance
Backflow prevention is not optional. A failed check valve on the injection line can allow fertiliser into a potable supply, and the resulting contamination is both a compliance and a reputational problem. Inspect non-return valves, vacuum breakers and air release points as part of a fixed schedule rather than after a visible failure. A practical maintenance routine includes weekly injector verification, differential-based filter cleaning, monthly flush of mains and laterals, seasonal acid treatment where scale is present, and a clear-water irrigation cycle after each fertigation event to rinse the system before it stands idle. Log every adjustment, because a dosing change made without a record is almost impossible to troubleshoot later. Finally, review site-specific conditions — greenhouse blocks with warm solution lines, orchard blocks with long laterals and elevation change, and field crops on variable soil — since each setting produces its own familiar failure pattern, and recognising it early is the difference between a small adjustment and a lost block.
