Root Electrical Capacitance

Definition

Root Electrical Capacitance is the measured capacitance, in nanofarads (nF), between a stem-base electrode and a substrate electrode under a low-amplitude AC excitation. The living root–substrate interface behaves as a distributed capacitor whose value scales with active (membrane-intact, water-absorbing) root surface area. At GreenWorld Sector-7 it is the only routine, non-destructive window onto below-ground vigour, sampled by PhytoSense Mesh root nodes.

Why it matters

Roots are invisible to every imaging channel, yet root loss is the root cause of many above-ground alarms — falling sap flow, rising leaf tension, growth stalls. Capacitance gives CHLORA a leading look at root health: a decline foretells reduced water-uptake capacity before the canopy expresses it, and it discriminates root failure from atmospheric stress when hydraulic channels disagree. It is a key input to root-zone irrigation and oxygenation control.

Formula

C_root = I_q / (2π·f·V)        (effective capacitance, nF)

measurement (PhytoSense Mesh root node):
  excitation: 1 kHz sinusoid, 1 V RMS
  electrodes: stem-base clamp ↔ substrate rod
  I_q = quadrature (90°) current component
  f   = excitation frequency, V = excitation voltage

temperature & moisture compensation:
  C_root normalized to 22 °C and to reference substrate
  moisture θ_ref via the node's paired EC/temp probe:
  C_norm = C_root · g(θ, T)

baseline:
  per-plant baseline set at establishment; metric trended
  as % of rolling 7-day baseline as well as absolute nF.

Reported to 1 nF.

Inputs

Units & Scale

nF, reported to 1 nF, normalized to 22 °C and reference substrate moisture. Trended both as absolute capacitance and as a percentage of the rolling 7-day plant baseline, since absolute values vary with plant size and substrate. Facility value is biomass-weighted. Confidence degrades when substrate moisture falls outside the compensation range (where the moisture correction grows large) or when electrode contact resistance exceeds the node's QC limit.

Sampling & Source

• Sampled every 30 minutes by PhytoSense Mesh root capacitance nodes.
• Normalized for substrate temperature and moisture before reporting.
• Trended as % of rolling 7-day baseline alongside absolute nF.
• Stale handling: flagged STALE after 60 min or on high electrode contact resistance.

Thresholds

Recent Trend

Facility biomass-weighted root capacitance, last 14 samples:

Interpretation Guidance

Related Metrics

Related SOPs

• SOP Library — root-node electrode placement & establishment-baseline capture.
• Root-decline WARN/CRIT triage & root-zone intervention — Operations SOP set in the SOP Library.
• Substrate oxygenation linkage & alarm escalation — Monitoring Systems.