Fertigation Calculator
Fertigation is where the fertiliser bill and the irrigation schedule meet. Get the concentration wrong in either direction and you burn roots or starve the crop.
Fertigation feeds the crop through the drip system: precise, frequent, and easy to over- or under-do because the maths is hidden inside a venturi dial. This tool makes it explicit — solution volume, product mass, nutrients delivered, concentration in ppm, and what the same weekly dose adds up to over a season. Use it with the fertiliser calculator, which sizes the season-long budget this tool executes.
Fertigation calculator
From product rate and application depth to ppm, weekly N and implied annual N.
The formulas#
Solution volume = depth (mm) × area (ha) × 10 ← 1 mm over 1 ha = 10 m³
Product per event = product rate (kg/ha) × area
N per event = product rate × N% ÷ 100 (kg/ha)
P₂O₅ / K₂O = product rate × P% or K% ÷ 100
Concentration = nutrient (kg/ha) ÷ solution (m³/ha) × 1,000 → ppm
Weekly N = N per event × events per week
Annual N = weekly N × fertigation weeks (40 assumed)Bananas take up nitrogen steadily once the root system is established; fertigation delivers it in small, frequent doses that match that uptake far better than two or three heavy broadcasts. The trap is that per-event dose, concentration and seasonal total are three different questions — a dose can look gentle in ppm and still oversupply the season if the events pile up.
Worked example#
2 ha, 10 mm events, 10 kg/ha CAN (27-0-0), twice weekly:
Solution volume = 10 × 2 × 10 = 200 m³ per event (100 m³/ha)
Product = 10 × 2 = 20 kg per event
N per event = 10 × 0.27 = 2.70 kg/ha → 5.4 kg on 2 ha
Concentration = 2.7 ÷ 100 × 1,000 = 27 ppm N
Weekly N = 2.7 × 2 = 5.4 kg N/ha/week
Annual N (40 wk)= 5.4 × 40 = 216 kg N/ha ✓ within 200–250Reading the results#
| Output | Why it matters |
|---|---|
| Solution volume | Pump run-time and whether the injector can dose that volume in one pass |
| N per event | The actual feed — compare against the fertiliser budget, not the product bag |
| Concentration (ppm) | Root-zone salinity risk: above ~250 ppm you can burn feeder roots |
| Weekly N | What the crop sees week to week — matches tissue-test interpretation |
| Implied annual N | The check that catches slow over-application: 40 weeks of "small" doses is still a season total |
Next steps#
- Water first: size the system with the irrigation calculator and schedule it with the irrigation scheduler.
- Set the seasonal nutrient budget: fertiliser calculator and the nutrition reference.
- Protect the drippers: filtration and flushing rules in water management.
- System components and injector ratios: the fertigation guide.