Tissue Hydration Index

Definition

The Tissue Hydration Index is the bulk water content of leaf tissue expressed as a percentage of fresh weight (% FW) — the mass of water per unit fresh tissue mass. It is the standing water reservoir of the leaf, a slowly varying state that the fast hydraulic channels (turgor, leaf water potential, conductance) draw against and modulate. At GreenWorld Sector-7 it is derived non-destructively by PhytoSense Mesh from leaf-clip dielectric and short-wave-infrared transmission, calibrated to gravimetric fresh/dry-weight references.

Why it matters

Hydration is the integrating water-status signal: turgor and potential swing diurnally around a hydration level that drifts only when supply and demand are chronically mismatched. A falling hydration baseline therefore flags a sustained deficit that diurnal channels can mask. CHLORA uses it as the slow set-point for irrigation volume (versus turgor for pulse timing) and as the bulk-water cross-check behind leaf water potential. It corroborates, rather than feeds, the CVI hydraulic sub-signals.

Formula

H = 100 · (FW − DW) / FW        (% fresh weight)

non-destructive estimate (PhytoSense Mesh leaf clip):
  H = a·ε_r + b·(−ln T_swir) + c

  ε_r    = leaf dielectric permittivity (50 MHz)
  T_swir = short-wave-IR transmission at 1450 nm
           (water-absorption band)
  a,b,c  = cultivar regression coefficients

calibration:
  coefficients fit per cultivar against gravimetric FW/DW
  (oven 70 °C, 48 h) at establishment; re-checked quarterly.

reference (relative water content, diagnostic):
  RWC = (FW − DW) / (TW − DW)   (TW = turgid weight)

Reported to 1 % FW.

Inputs

Units & Scale

% fresh weight, reported to 1%. Healthy hydrated leaves sit in the high 80s; the metric has a narrow operating range, so single-point changes are significant. Aggregated per cohort as the median; facility value is cohort-count-weighted. The diagnostic relative-water-content (RWC) form is logged alongside. Confidence degrades when cultivar coefficients are overdue for quarterly re-fit or when clip leaf temperature falls outside 18–30 °C.

Sampling & Source

• Sampled every 15 minutes by PhytoSense Mesh dielectric/SWIR leaf clips.
• Calibrated per cultivar against gravimetric FW/DW; re-checked quarterly.
• Read as the slow irrigation-volume set-point alongside turgor for pulse timing.
• Stale handling: flagged STALE after 30 min; overdue-coefficient cohorts low-confidence.

Thresholds

Recent Trend

Facility cohort-weighted tissue hydration, last 14 samples:

Interpretation Guidance

Related Metrics

Related SOPs

• SOP Library — gravimetric FW/DW calibration & quarterly coefficient re-fit.
• Hydration-deficit WARN/CRIT triage & irrigation-volume response — Operations SOP set in the SOP Library.
• Irrigation-volume linkage & alarm escalation — Monitoring Systems.