Granular, liquid, foliar and fertigation: how the method changes the result
Quick answer
Where and how you put a fertiliser matters as much as which one you choose. Granular products need to reach the root zone and be watered in. Fertigation delivers nutrients with irrigation and needs highly soluble products. Foliar sprays bypass the roots and must be dilute. Each has a failure mode: granules left dry on an alkaline surface lose nitrogen to the air, emitters clog, and a concentrated foliar spray damages the leaf it was meant to feed.
Soil application (granular)
The nutrient has to arrive where roots actually are. FAO lists among the conditions for optimal nutrition: sufficient available nutrients in the root zone, rapid transport of nutrients in the soil solution towards the root surface, and satisfactory root growth to access them. A granule outside the root zone meets none of those conditions.
There is a specific loss to avoid here. FAO warns that losses of nitrogen as gaseous ammonia occur in the neutral to alkaline range where nitrogen fertilizers — particularly urea — are applied to the soil surface and left unincorporated. On an alkaline soil, scattering urea and leaving it dry loses part of it to the air.
Fertigation
FAO defines fertigation as applying fertilisers together with irrigation water rather than as a separate operation, more often advocated with drip than with flood irrigation, and notes that in principle all required nutrients including micronutrients can be applied this way. Products must be highly water soluble.
Its regional advantage is real: FAO notes that where irrigation water contains dissolved salts, drip is particularly suitable because less water is applied than with surface methods. The same network suits both problems.
Its cost is equally real: drip and sprinkler are technically more complicated methods, and sediments may clog emitters.
Foliar application
Leaves can absorb nutrient ions and some molecules. FAO explains that nutrients enter either via the stomata or mainly via small micropores of the cuticle into the apoplast.
The safety rule is FAO's own and is not optional: foliar application is carried out through dilute solutions in order not to damage the leaf cells by osmotic effects. A stronger spray does not feed the plant better; it burns it.
Foliar feeding is a fast corrective, particularly where root uptake is impaired — as on alkaline calcareous soil where micronutrients are fixed. It does not fix the soil condition underneath.
Deciding which method
- Is this a correction or routine nutrition? A correction favours a fast route; routine nutrition favours placement in the root zone.
- Is the limitation supply or uptake? If roots cannot take the nutrient up because of soil chemistry, adding more to the soil repeats the problem.
- What does your irrigation allow? Fertigation needs a working, filtered drip network and soluble products.
- Can it be watered in? If not, a surface-applied nitrogen product is a poor choice.
- Confirm against the label. The label states which methods a product is made for.
In Kuwait's conditions
Dust is the practical constraint on fertigation. FAO notes that sediments may clog drip or sprinkler systems, and Kuwait's dust is seasonal and predictable rather than exceptional — the Al-Sarayat season from 9 April is characterised by severe dust storms, with summer peaks on 9–12 and 17–24 June and 1–7 and 9–17 July. Filters need checking after storms, not after failure.
Heat is the constraint on foliar spraying: with summer maxima of 42–46°C, spraying a stressed plant in high heat raises the risk of leaf damage.
Alkalinity is the constraint on surface granules, through the ammonia loss described above.
Common mistakes
- Placing granular fertiliser against the trunk instead of in the root zone.
- Broadcasting urea on dry alkaline soil and not watering it in.
- Making a foliar spray stronger than the label says, believing it will work better.
- Running a poorly soluble product through drip emitters.
- Treating a foliar spray as a cure for a soil problem rather than a temporary correction.
Boundary
No concentration, dilution ratio, injector setting, emitter spacing or application rate is given here. Those are engineering and label decisions that depend on your water source, pressure, soil texture, area and product. Foliar concentrations in particular must come from the product label — exceeding them causes damage.
Related glossary terms
Sources
- FAO — Fertilizer and Plant Nutrition Bulletin 16. FAO, Rome, 2006. ISBN 92-5-105490-8. Chapters 3, 4, 5 and Glossary.
- FAO — Irrigation Water Management Training Manual No. 5: Irrigation Methods. fao.org
- Kuwait Meteorological Department — Climate. met.gov.kw
All accessed 26 August 2026. Last reviewed: 27 August 2026.