A few issues ago, I wrote about an experiment performed in the 1930s by Sister Mary Etienne Tibeau. She conducted various fertilizer experiments with hemp—depriving seedlings of all fertilizers or giving them a complete fertilizer (except that it lacked Nitrogen).
I have been replicating that experiment. I germinated the seeds between two layers of hand towel cloth, and then planted them in rockwool cubes. They were supplied with tap water that had 70 parts per million (ppm) dissolved solids but no Nitrogen. They were kept under constant fluorescent light for 10 days and then the lighting was changed to 12 hours with each light and uninterrupted darkness to induce flowering.
The plants are growing very slowly without nutrients. They look comparable to the seedlings that Tibeau recorded in her studies. As you can see in the second photo below, they are beginning to form primordial flowers. At this point, their sex cannot be determined. By next month, we will see if the lack of Nitrogen has an effect on sexual expression, as Tibeau reported.
I first saw the use of CO2 outdoors when I was on a trip to Australia. A single cannabis plant was growing in the yard next to the house [that I was at]. A gas water heater was sitting outside, to one side of the plant. Every time the hot water was turned on, the propane was fired. It heated the water as well as produced CO2 and water vapor. The side of the plant receiving the gas was much more robust than the other side. This was an extremely well done, albeit an inadvertent experiment. It was performed on a single plant so the genetics was the same, as well as all environmental conditions except for the enhanced CO2 on only one portion of the plant. This showed that even outdoors, CO2 enhanced air results in higher yields.
I recently visited a legal cannabis farm in California too, where the cultivators were performing CO2 experiments on open tunnel gardens in order to learn the most efficacious way to supply it.
They have a large tank of liquid CO2, which is held under pressure. The gas is delivered to the top of the canopy through tubing with micro-pore holes to release the gas. CO2 is heavier than air and it is cold so it drifts down to the plant tops. Light intensity, wind and temperature are all taken into account as they are developing logarithms for gas release. Results will be tallied after harvest.
Meanwhile, you can try this method on your own. Regulate the gas tank using a timer and CO2 ppm meter. Set the timer to release the gas between 11 a.m. and 3 p.m., when the sun is most intense. Set the ppm meter to about 800 ppm. This turns the gas flow on and off which keeps the CO2 levels stable. Don’t run it on windy days though, you’ll just be wasting gas.