Does Granular Fertilizer Also Cake? -Causes of fertilizer caking and how to prevent it – a practical guide for manufacturers.
Many fertilizer manufacturers assume that once the material is granulated, caking is no longer a problem. But in reality, granular fertilizer does cake — and often in ways that are more frustrating than powder caking.
Granule caking is not about the granules physically sticking together. It happens due to surface dissolution and re-crystallization, which forms solid bridges between particles.
Why Does Granular Fertilizer Cake?
| Cause | Mechanism | Typical Sign |
|---|---|---|
| Moisture migration | Internal moisture moves to the surface and evaporates, leaving crystal bridges between granules | Granules become “welded” together |
| Storage pressure | High stacking pressure deforms granules, increasing contact area and bonding | Bottom layers cake much harder than top layers |
| Temperature fluctuation | Day‑night cycles cause repeated moisture absorption and evaporation | Caking is worse in spring and autumn |
| Rough granule surface | Porous or uneven surfaces absorb moisture more easily | Low‑end granulation equipment leads to more caking |
| Hygroscopic raw materials | Urea, ammonium nitrate, etc., naturally absorb moisture from air | High‑N formulas cake more easily than high‑K formulas |
A typical example: granules come out of the dryer with only 1.5% moisture. During ocean shipping, day‑night temperature changes cause moisture to migrate to the surface. After 40 days, the bags arrive hard as cement. The customer doesn‘t blame the shipping — they blame your fertilizer.
How to Diagnose the Caking Type
| Phenomenon | Possible Cause | Solution |
|---|---|---|
| Whole bag hard, but can still be broken | Moisture too high (>2.5%) or packing temperature too high | Improve cooling, control packing temperature |
| Hard core in the middle, loose around the edges | Moisture absorption during storage or over‑stacking | Improve warehouse conditions, limit stack height |
| White powder on granule surface | Low granule strength or rough surface | Optimize granulation, add polishing or coating |
| Caking varies significantly by formula | Different hygroscopicity of raw materials | Adjust formula or apply targeted coating |
How to Prevent Granular Fertilizer Caking
| Solution | Effect | Best For |
|---|---|---|
| Control drying & cooling | Keep moisture <2%, packing temperature <40°C | All production lines (must-have) |
| Improve storage conditions | Moisture-proof, ventilated, stack height ≤10 layers | Long-term storage or sea shipment |
| Optimize granulation | Higher granule strength, smoother surface | Premium products, export orders |
| Use anti-caking agent | Powder or liquid coating | Cost-effective, simple process |
| Apply coating film | Forms a hydrophobic protective layer on granule surface | High‑N formulas, long‑term storage, humid environments |
Good drying and cooling can solve about 50% of caking problems. For the remaining 50% — especially in humid seasons or for sea shipment — conventional anti‑caking agents may not be enough. A hydrophobic coating is the more reliable solution.
Final Thought
Many fertilizer manufacturers blame caking on “poor raw materials” or “improper customer storage.” But the truth is: with the same production line and the same raw materials, orders with coating have zero complaints, while orders without coating come back with problems every summer.
Caking is not a “quality issue” — it‘s a process choice.
If your fertilizer also tends to cake, maybe it’s time to look at your drying, cooling, and coating process.