The "Plant Growth" parameter calculates the difference in weight between two consecutive days and should represent the daily biomass gain of the plant.
It is calculated as: Plant Weight reference time (n+1) - Plant Weight reference time (n), n(day).
*The Plant Weight reference time is the average weight after irrigation as defined in the "Experiment" tab in Planarray Client:
Under well-irrigated conditions (regular night irrigations), values of "Plant Growth" are expected to be around zero or positive when the plant grows. In times of water shortage (drought treatment or alike) "Plant Growth" will be negative.
However, even under well-irrigated conditions, sometimes negative values are observed.
There could be different causes for this phenomenon. Calculation of "Plant Growth", assumes that all components besides the plant remain the same weight after irrigation and drainage. Negative values indicate that this assumption has been violated for some reason.
Possible causes and solutions:
Cause: The soil/medium reaches over its capacity (in comparison to the maximum capacity when irrigating with the system) due to manual irrigation that occurred prior to loading the pots. Changing the irrigation method might cause weight loss of water.
Solution: Irrigate regularly with the system (multiple pulses of water during the night, each reaching drainage) for a few days so that the pot water capacity can be stabilized.
Cause: Insufficient watering - the applied irrigations do not get the pots to full water capacity (drainage peaks are not observed).
Solution: Increase the amount or number of irrigation, ensuring each of them reaches drainage.
Cause: Medium is not draining well or absorbing too much water - clayey soils might not drain fast enough and mediums with high organic matter content like peat-based substrates might keep on absorbing water for a long time. These characteristics might make it difficult to maintain a stable weight every day.
Solution: Try to change the irrigation pattern - for example, fewer pulses with more water each. If the issue remains, consider using another medium (or change the ratios if using a mix) that drains well and does not retain a lot of water.
Cause: High variability of weather conditions (VPD/light intensity) might cause inconsistent recharge of water to the pot capacity, especially when daily transpiration is low.
Solution: Consider using light and/or climate control measures to achieve more stable conditions.
Cause: Drainage problems - sometimes drainage might be partially blocked or affected by the presence of different substances like fertilizer sediments or soil/plant secretions.
Solution: Make sure that the reservoir container (drainage container that the pot is located in) is clean and not blocked by many roots or soil residues. Make sure that the silicon drainage plug is positioned well and clean from sediments or roots.