Simple. But I see two answers here:
1. Just list all the equipment that uses compressed air and sum all values to get to to the number to choose your compressed air. Make sure to make all fit within the pressures you expect to have available, and calculate through volumetric flow or mass flow.
2. Take your plant and build a translucid enclosure air tight. Then, you'll need some sort of oxygen analyser to measure the oxygen content of the enclosure around the day, you'll need probably to make compensations for light incidence, provide means to adjust humidity in the roots, etc. Quite a large job. Have you googled for information on a more dedicated blog? Hehehe.
Rgds.