Use mg/L for nutrient concentration. Leave pH, temperature, or EC empty to ignore that factor.
Sample inputs and calculated outputs for a typical 7-day period.
| Water (L/day) | Days | N (mg/L) | P (mg/L) | K (mg/L) | Eff. (%) | Stage | pH | Temp (°C) | EC (mS/cm) | Avail. factor | Total uptake (g) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 3.5 | 7 | 180 | 45 | 200 | 65 | 1.00 | 6.1 | 21 | 2.2 | ~1.000 | ~5.48 |
| 2.0 | 10 | 150 | 35 | 180 | 55 | 0.90 | 7.2 | 28 | 3.8 | ~0.504 | ~1.83 |
| 5.0 | 14 | 200 | 50 | 260 | 70 | 1.20 | 5.6 | 16 | 2.9 | ~0.810 | ~15.28 |
Values are illustrative. Your crop, light, media, and irrigation pattern can shift actual uptake.
For each nutrient (N, P, K), the estimated uptake over the selected period is:
Uptake(g) = Water(L/day) × Days × Concentration(mg/L) × (Efficiency/100) × Availability × Stage ÷ 1000
- Availability = pH factor × temperature factor × EC factor (bounded).
- pH factor is highest near 5.8–6.5 and declines outside.
- Temperature factor is highest near 18–24°C and declines outside.
- EC factor reduces uptake as salinity increases.
- Measure or estimate average daily water uptake for your plant or zone.
- Enter nutrient concentrations in mg/L for N, P, and K.
- Set an uptake efficiency based on your system and losses.
- Pick a stage factor to reflect crop growth demand.
- Optionally provide pH, temperature, and EC for stress adjustment.
- Click Calculate to view results above the form.
- Use Download CSV or Download PDF to save outputs.
Tip: If totals look high, reduce efficiency or check your water uptake estimate.
Water uptake as the driver of nutrient flux
Water movement through the root zone is the main conveyor of dissolved nutrients. When daily uptake rises, the plant can access more solution volume, increasing potential intake of N, P, and K. The calculator starts with water uptake because it scales everything else. Use measured irrigation totals, drainage records, or container weight changes to estimate realistic liters per day for your crop.
Concentration and unit discipline
Solution strength is entered as mg/L, which is equivalent to parts per million in dilute water. Keep labels consistent with your fertilizer plan, especially when converting from product grams or from elemental versus oxide reporting. If you only know total dissolved solids, treat it as a screening metric and still obtain nutrient-specific concentrations for decisions. Small unit errors can create large uptake errors.
Efficiency represents system losses
Uptake efficiency accounts for real-world losses such as runoff, leaching, uneven wetting, and incomplete absorption. In soil beds, efficiency may be lower during heavy irrigation or sandy media. In recirculating systems it may be higher, but still imperfect due to precipitation, biofilm, or bypass flow. Start with a conservative percent, then refine using tissue tests and observed growth response.
Stress factors: pH, temperature, and EC
Nutrient availability changes when chemistry and physiology shift. A pH outside the preferred band reduces solubility and transporter activity. Cool or hot root zones slow metabolism and water movement. Higher EC increases osmotic stress, often lowering water uptake and nutrient flow. The calculator combines these as an availability factor to temper the idealized intake estimate. Leave fields blank if you lack data.
Turning outputs into an action plan
Use grams per day to compare feeding targets across growth stages and to spot mismatches between supply and demand. If estimated uptake is high, verify that stock tanks and injectors can maintain concentration without swings. If uptake is low, investigate water uptake, root health, or salinity rather than only increasing fertilizer. Update inputs weekly to reflect weather, canopy size, and stage factor changes. Pair the estimate with leaf color, vigor, and runoff EC trends to validate that nutrition stays balanced overall.
1) What does the availability factor mean?
It is a combined adjustment for pH, root temperature, and EC. It reduces ideal uptake when conditions limit solubility or plant transport processes.
2) Should I enter elemental N, P, and K values?
Yes, enter elemental nutrient concentrations in mg/L. If your label lists oxides like P2O5 or K2O, convert to elemental before entering.
3) How can I estimate daily water uptake accurately?
Track irrigation applied and subtract drainage, or weigh containers before and after irrigation cycles. Average several days to smooth weather-driven swings.
4) Why does higher EC lower the estimate?
Higher EC increases osmotic pressure, making it harder for roots to pull water. Reduced water flow often reduces nutrient flow and slows growth.
5) How often should I update the inputs?
Update weekly or whenever canopy size, climate, or irrigation strategy changes. During rapid growth or heat, update more frequently.
6) Can this be used for foliar feeding plans?
Not directly. Foliar uptake follows different pathways and rates. Use this tool for root-zone solution delivery and adjust foliar programs separately.