Nutrient Conductivity (EC)

Definition

Nutrient Conductivity (EC) is the electrical conductivity of the nutrient solution in the root zone or fertigation loop, measured in millisiemens per centimetre and referenced to 25 °C. Conductivity rises with dissolved ion concentration, so EC is the standard proxy for total salt strength of the feed. It is sensed directly by graphite or toroidal EC cells on the PhytoSense Mesh in the supply line and at representative root zones, each reading temperature-compensated so that thermal effects are not mistaken for fertility changes.

Why it matters

EC sets how hard the plant must work to draw water. Too low and the canopy is under-fed, growth slows, and deficiency symptoms appear; too high and osmotic pressure rises until water uptake is suppressed even when substrate moisture (VC-MET-106) looks adequate — a salt-induced drought. EC is also the closure check on the fertigation system: divergence between supply and root-zone EC reveals salt accumulation or leaching. CHLORA doses concentrate and dilution water to hold EC in band against the live dry-down.

Formula

A directly measured signal. Reported EC is the temperature-compensated cell reading normalized to 25 °C:

EC_25 = EC_raw / ( 1 + α·(T − 25) )

  EC_raw  measured conductivity (mS·cm⁻¹) at solution temp T
  T       solution temperature (°C)
  α       temperature coefficient ≈ 0.019 /°C (nutrient soln)

Cell calibration:
  K_cell from 1.413 / 12.88 mS·cm⁻¹ standards.
Supply vs root-zone:
  ΔEC = EC_root − EC_supply ; rising ΔEC ⇒ salt build-up,
  triggering a leaching-fraction increase.

Inputs

Units & Scale

Reported in millisiemens per centimetre to one decimal place, normalized to 25 °C. EC is intensive and not summed; the operational figure is the supply-line EC, with root-zone EC reported alongside as a salt-accumulation check. Confidence degrades to DEGRADED when root-zone EC exceeds supply EC by > 0.8 mS·cm⁻¹ (salt build-up needing a leach) or when a cell's calibration constant has drifted beyond tolerance at the last standard check.

Sampling & Source

• Sampled every 5 minutes from the PhytoSense Mesh EC cells in supply and root zone.
• Temperature-compensated to 25 °C using the inline solution-temperature reading.
• Stale handling: a cell silent > 15 min is dropped; loss of the supply cell suspends EC-based dosing with a DEGRADED flag and holds the last valid recipe.
• Calibration: weekly two-point check (1.413 / 12.88 mS·cm⁻¹); cell-constant drift > 3 % raises a metrology work order.

Thresholds

Recent Trend

Zone-A supply-line EC, last 14 sampling roll-ups (mS·cm⁻¹):

Interpretation Guidance

Related Metrics

Related SOPs

• SOP Library — fertigation dosing & leaching procedures.
• Salinity flush response on high-EC CRIT — see Environment SOP set in the SOP Library.
• Dosing-pump interlock & alarm escalation — Monitoring Systems.