A jar test is a small-scale mixing test that shows whether a lignosulfonate product stays compatible with the other components of a tank mix or liquid fertiliser before it is used in the field. It checks for precipitation, gelling, separation, foaming and pH change, using the same water, order of addition and concentrations as the real mix.
What You Need
- Clear 1 L jars or beakers with lids
- The same water that will be used in the sprayer or fertigation system
- All products in the planned mix, at the planned rates scaled to 1 L
- Graduated cylinders or syringes, pH meter or strips, a timer
- A fine sieve (for example 100 mesh / 150 µm) to check for residue
Step-by-Step Procedure
| Step | Action | What to look for |
|---|---|---|
| 1 | Fill the jar with half the water volume | Record water pH and, if known, hardness |
| 2 | Add products in the planned order (common order: water-dispersible solids, liquids that need dispersing, solutions such as lignosulfonate, then surfactants/adjuvants) | Mix gently after each addition |
| 3 | Add the lignosulfonate product at the scaled rate, for example 1–3 g/L for a foliar Zn-LS powder | Clumps, slow dissolution, colour change |
| 4 | Top up to volume, close and invert 10 times | Foam height |
| 5 | Let stand 30 minutes | Layers, flakes, sediment, gel, oil separation |
| 6 | Invert again and pour through the sieve | Residue that could block nozzles or drippers |
| 7 | Measure pH; for fertigation, leave a second jar for 24 hours | Late precipitation, especially with phosphates or calcium |
Reading the Results
| Observation | Likely cause | What to try |
|---|---|---|
| Precipitate after adding phosphate | Calcium or micronutrient phosphates forming | Change order, lower concentration, use separate tanks or a different micronutrient form |
| Gel or thickening | High concentration or incompatible polymer | Dilute; pre-dissolve lignosulfonate |
| Flakes with calcium nitrate | Calcium reacting with sulphate or phosphate | Do not mix concentrates; inject separately |
| Strong foaming | Surfactant interaction | Add surfactant last; use antifoam if allowed |
| No change after 30 min and 24 h, passes sieve | Physically compatible | Proceed to a small field check |
Limits of a Jar Test
- It checks physical compatibility only, not crop safety or biological efficacy.
- Temperature matters: test at the temperature of the field water.
- Concentrated stock solutions for fertigation behave differently from diluted spray mixes; test both if both are used.
- Liquid micronutrient lignosulfonates such as the 45%-solids Zn-LS grade should be shaken before use if stored for a long time.
Frequently Asked Questions
Why is a jar test needed for lignosulfonate fertilisers?
Lignosulfonate is compatible with many fertilisers, but calcium, phosphates, hard water and some pesticides can cause precipitation. A jar test reveals this before it blocks a sprayer or dripper.
How long should a jar test run?
At least 30 minutes for spray mixes; for fertigation stock solutions, also check after 24 hours.
Does passing a jar test mean the mix is safe for the crop?
No. It shows physical compatibility only. Check product labels and run a small field test for crop safety.
References
- Green Agrochem TDS GAC-ZnLS (zinc lignosulfonate) and GAC-ZnLS-L45 (liquid zinc lignosulfonate, 45% solids)
Related Pages
Questions about a specification, a test method or a trial: contact us or email info@greenagrochem.com.
