A blocked emitter does not announce itself. It produces a plant that is slightly behind its neighbours, then a patch that is noticeably behind, and by the time the pattern is obvious the season has moved on. The cost is uneven crop and remedial labour, and almost all of it is preventable.
Blockages come from three sources: physical particles, biological growth, and chemical precipitation. The third is the one growers create themselves, and it is the one this article concentrates on.
Chemical precipitation: what reacts with what
Some fertilizers, when concentrated together, form compounds that will not dissolve. The reaction happens in the stock tank or in the injection line, and the resulting solid ends up in your filters and emitters.
Calcium + phosphate
The most common and most damaging combination. Concentrated calcium nitrate and concentrated phosphate — MKP, MAP or phosphoric acid — form calcium phosphate, which is essentially insoluble. It appears as a white sludge in the tank and a hard scale in the lines.
Calcium + sulphate
Concentrated calcium and concentrated sulphate — magnesium sulphate or potassium sulphate — form calcium sulphate, gypsum. Less aggressive than calcium phosphate but still a scale-former.
High pH + calcium or magnesium from the water itself
Water with high bicarbonate and high calcium will deposit carbonate scale in the lines whenever pH rises, quite independently of what you inject. In hard-water regions this is a continuous background process.
Iron and manganese oxidation
Groundwater containing dissolved ferrous iron will oxidise on contact with air, forming reddish-brown ferric deposits. Manganese behaves similarly, producing black deposits. Both foul filters and emitters.
Humic products in acidic concentrate
Concentrated humic acid mixed with strongly acidic concentrate will precipitate. Dose humic products separately or at final dilution.
The two-tank rule
The solution to nearly all of the above is separation. Use two stock tanks and keep incompatible products apart until final dilution, where concentrations are low enough that nothing precipitates.
Tank A
Calcium nitrate. Iron chelate and other chelated micronutrients. Potassium nitrate (compatible with either tank).
Tank B
Phosphates — MKP, MAP, phosphoric acid. Sulphates — magnesium sulphate, potassium sulphate. Ammonium sulphate. Potassium nitrate if you prefer it here.
Never
Calcium in the same concentrate as phosphate or sulphate. This is the rule that matters.
If you use acid for pH correction, inject it separately or into Tank B. Never add concentrated acid directly to concentrated calcium nitrate.
Practical rules for mixing
- Dissolve fully before injecting. Undissolved crystals will find their way into the line. Agitate until the solution is clear, then wait.
- Allow more time for low-solubility products. Potassium sulphate needs considerably more mixing than potassium nitrate. Cold water slows everything.
- Add one product at a time. Let each dissolve completely before adding the next.
- Watch water temperature. Solubility falls with temperature, and potassium nitrate dissolving actually cools the tank. In winter, allow more time or use slightly warmer water.
- Do not over-concentrate stock tanks. Running near saturation means anything — a temperature drop overnight, a slight excess — pushes material out of solution.
- Jar-test anything new. Before committing a new combination to a full tank, mix a small sample at the same concentration and leave it for an hour. Cloudiness or sediment is your answer.
The other two causes
Physical particles
Sand, silt and organic debris from the water source. Managed with correctly specified and correctly maintained filtration:
- Match filter type to contaminant — screen or disc for inorganic particles, sand media for organic loads and algae
- Size the filter for the flow rate and specify mesh appropriate to the emitters, not just to the pump
- Check and clean on a schedule, not when a problem appears
- Watch pressure differential across the filter — a rising differential is the earliest warning you will get
Biological growth
Algae, bacterial slimes and iron-oxidising bacteria. Nutrient-rich water in warm conditions is an ideal growth medium, and the biofilm that forms traps particles and creates the blockages.
- Keep tanks and lines out of direct light where possible — light drives algal growth
- Cover open tanks
- Flush laterals regularly, particularly line ends where velocity is lowest
- Where biological fouling is persistent, discuss appropriate treatment with your irrigation supplier and follow the label and local regulations
A maintenance routine
Every irrigation
- Run clean water for a few minutes at the end of each fertigation cycle so nutrient solution does not sit in the lines between events
Weekly
- Check pressure at the start and end of representative laterals — a growing difference means restriction is developing
- Inspect filters and clean as needed
- Walk a sample of the block and check emitter output visually
Monthly
- Flush lateral line ends until water runs clear
- Measure output from a set of marked emitters and compare with their rated flow
- Inspect stock tanks for sediment
Each season
- Full system flush before and after the crop
- Review the water analysis — sources change
- Review the fertilizer programme for any new incompatibility
Diagnosing an existing problem
The deposit usually identifies its own cause:
| What you find | Likely cause |
|---|---|
| White, chalky, hard scale | Calcium carbonate or calcium phosphate |
| White soft sludge in the tank | Calcium phosphate or gypsum from mixed concentrates |
| Reddish-brown deposit | Iron oxidation |
| Black deposit | Manganese oxidation |
| Slimy, soft, green or brown | Biological growth |
| Gritty sediment | Physical particles — check filtration |
Summary
- Never mix concentrated calcium with concentrated phosphate or sulphate — use two stock tanks
- Dissolve everything fully before injection, allowing extra time for low-solubility salts and cold water
- Jar-test new combinations before committing a full tank
- Keep pH in the delivered solution around 5.5–6.2 to reduce carbonate scaling
- Flush lines and clean filters on a schedule; watch pressure differential as an early warning
- Identify a deposit by colour and texture before deciding on treatment
If you would like your fertilizer programme checked for compatibility before the season starts, send us the product list and your water analysis. It takes a few minutes and it is considerably cheaper than replacing a block of emitters. See also the fertigation guide.
Need this product, or advice on which grade fits?
Send us the crop, your water analysis and the quantity you need. We will reply with the options that actually apply to your situation.
