water-dynamics → rewetting-hysteresis
Dry substrates do not behave the same way when rewetted.
This phenomenon is known as rewetting hysteresis and explains why irrigation “stops working” after dry periods.
Hysteresis means: - The wetting path differs from the drying path - Moisture behaviour depends on history
Once a medium dries beyond a threshold, it resists rewetting.
Drying causes: - Organic coatings to repel water - Pore structure collapse - Air entrapment - Preferential flow dominance
Water bypasses dry zones instead of rehydrating them.
Common signs include: - Runoff or channeling - Wet surfaces with dry root zones - Patchy moisture distribution - Wilting despite irrigation
Adding more water often makes the problem worse.
Rewetting requires: - Time - Lower application rates - Repeated small pulses
Rapid application overwhelms infiltration capacity.
Dry zones concentrate salts.
On rewetting: - EC spikes locally - Roots are damaged - Uptake is disrupted
This amplifies stress during recovery.
Effective rewetting strategies include: - Avoiding excessive dry-down - Using multiple short irrigation pulses - Reducing application rate - Allowing time between pulses - Monitoring moisture depth, not surface wetness
Key mistake: - Attempting to “flush” a dry medium in one event
Once media repel water, patience beats volume.