Model ion-specific UCF dynamics in recirculating & drain-to-waste hydroponic systems
Select a crop preset or configure custom parameters. UCF = Uptake Concentration / Supply Concentration.
| Ion | Supply (mmol/L) | Plant Uptake (mmol/L) | UCF | Drain (mmol/L) | Accumulation Risk | Action |
|---|
The UCF describes the ratio at which a plant absorbs a specific nutrient relative to water. It is defined as the ratio of ion concentration in the plant uptake solution to the ion concentration in the supply solution:
When UCF > 1.0, the plant preferentially absorbs that ion (active uptake), causing its concentration in the drain to decrease. When UCF < 1.0, the ion accumulates in the root zone and drain solution (passive exclusion).
For recirculating systems, the drain EC increases with each cycle as excluded ions (Na⁺, Cl⁻, SO₄²⁻) accumulate:
Where DF = Drain Fraction (volume drain / volume supplied). Typical greenhouse drain fractions range from 20-40% depending on substrate, climate, and crop.
EC readings are temperature-dependent. The standard reference is 25°C. The correction factor is approximately:
where T is the solution temperature in °C and 0.02 is the approximate coefficient for most nutrient solutions.
In recirculating systems, Na⁺ accumulates because plants have near-zero uptake (UCF ≈ 0.05). The critical threshold for most greenhouse crops is Na⁺ < 8 mmol/L in drain. When exceeded, the system must be partially or fully flushed.
Modern commercial greenhouse fertigation balances matric potential, osmotic pressure, and stoichiometric ionic ratios in inert substrates such as rockwool or coir. Crops absorb water and essential mineral nutrients through specialized ion transport proteins in root epidermal cells. The total suction pressure required for water extraction is the sum of substrate matric suction (determined by pore capillary diameter) and osmotic suction (proportional to electrical conductivity, EC). Crop steering leverages diurnal substrate dry-back percentages: a larger morning dry-back (8–12%) generates mild osmotic stress that steers plants generatively (flowering and fruit set), whereas smaller dry-backs (< 5%) with higher runoff volume steer plants vegetatively (leaf canopy expansion and vegetative vigor).
| Crop / System State | Target Setpoint | Engineering Range | Operational Impact |
|---|---|---|---|
| Rockwool Slab Water Content (WC) | 55 – 75% | Peak after midday irrigation | Daily dry-back: 8 – 12% |
| Coco Coir Slab Water Content (WC) | 60 – 80% | Higher water retention capacity | Daily dry-back: 6 – 10% |
| Vine Tomato Rootzone EC | 3.0 – 4.2 mS/cm | Slab EC typically +0.5–1.0 mS/cm over dripper EC | Target Drain: 25 – 35% |
| Cucumber Rootzone EC | 2.2 – 2.8 mS/cm | Lower salinity threshold, high water demand | Target Drain: 30 – 40% |
| Sweet Pepper Rootzone EC | 2.8 – 3.5 mS/cm | Sensitive to sudden osmotic swings | Target Drain: 20 – 30% |
Commercial precision horticulture demands lab-grade sensors and field calibration meters. The following industrial-grade instruments are vetted for validating the inputs and outputs of this calculator:
Laboratory-grade dual electrochemistry meters with automatic temperature compensation (ATC) for precision hydroponic nutrient management.
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