Substrate Dryback
The reduction in substrate water content between irrigation events. Dryback is used to steer root zone conditions, oxygen availability, and plant growth patterns.
Substrate dryback is the drop in water content that occurs between irrigation events. It is commonly tracked as a percentage change in substrate moisture, container weight, or sensor reading from full saturation to the next irrigation.
In controlled indoor environments, dryback is a key irrigation management tool. A smaller dryback keeps the root zone more consistently moist and can support steady vegetative growth. A larger dryback increases oxygen exchange, concentrates the root zone solution, and can be used as part of crop steering when applied carefully.
Common dryback references:
- Overnight dryback: moisture loss from the last irrigation of the day to the first irrigation the next day
- Inter-irrigation dryback: moisture loss between daytime irrigation events
- Total daily dryback: the overall change across a full light cycle
Dryback should not be managed by moisture alone. It interacts with EC, substrate volume, root mass, light intensity, airflow, and temperature. Excessive dryback can stress roots and increase salt concentration, while insufficient dryback can reduce oxygen availability and slow root function.
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