How to measure the biomass of hydroponic plants in netpot/rockwool DWC system?
If you did enough replications in your experiment, you could harvest one or more plants and measure fresh weight, and then gently oven dry for about 48 hours at like 160 degrees F and then take a dry weight as a measure of biomass. I don't know a non-destructive way to do it. A lesser alternative would be to measure plant height and number of leaves, though this would be less accurate. There are devices that measure leaf area, and I know a simple, low-tech way to measure leaf area.