Why and How to Supplement CO2 in Indoor Farms
Carbon: crucial to growth, but under-managedCarbon is one of the most abundant element in plants, and is extremely important to plant structure and growth. Many farmers take carbon for granted, but indoor farmers can increase yield by taking an intentional approach with carbon. Since carbon leaves the farm when you harvest (removing plant matter), farmers need to get carbon back into the farm. Farmers do this when they supplement CO2 in indoor farms. In this post, we’ll discuss how CO2 supplementation can increase yields (important especially indoors) and the three main ways that farmers supplement CO2.
Why should growers supplement CO2 in indoor farms?
CO2 uptake allows for plant growth
When it comes to the relationship between plants and CO2/carbon, several things take place:Plants fix carbon from CO2 in the air by passive diffusion. (The CO2 passes from an area of higher concentration – the air- to an area of lower concentration – the plant tissues.) Because the plant uses the difference in concentrations to take up CO2, the concentration of CO2 in the air is very important. After being taken up by the plant, the CO2 is transformed into sugars used for plant growth. Ultimately, that carbon makes it possible for plants to grow new tissues and stay strong. If the CO2 levels in a growing environment get below about 250 ppm, the plants stop growing.
Growers need to replace the carbon that they remove from the farm during harvest
After the plant uses the carbon from CO2 to build plant tissues, the next step is harvesting. Every time you harvest, you’re taking carbon out of the farm, because you’re removing (carbon-rich) plant tissues. To maintain a high level of carbon on your farm, growers must replenish that carbon through CO2.
If CO2 levels are too low, it becomes the limiting variable; it won’t matter how much light and nutrition you have. Your yield will bottleneck. In this case, you’re essentially wasting the other inputs that you’re paying for in your system.
For indoor growers, replenishing CO2 will usually require that the grower actively puts CO2 back into the farm atmosphere. For most growers, just a few dollars a day in CO2 can boost plant yield by about 30%.
Measure CO2 with handheld sensors or a climate control system
The first step in the CO2 supplementation process is deciding whether or not your levels are too low. Most environment control systems (like the IntelliClimate) have built in sensors for CO2 . There are also several handheld or wall-mount sensors that will tell you what the CO2 is for your facility.
Most indoor growers should have CO2 between 800 and 1200 ppm. Some growers have used closer to 1500, but there is a law of diminishing returns at that point; for most people, 1200 is the highest they should go.
At this range, the exchange process is very quick and easier on the plant, and the plant also becomes more water efficient. (Higher CO2 can reduce the need for transpiration and water use in your system.)
3 main ways to supplement CO2 in indoor farms:
1) Burn a fuel like natural gas or propane.
As you’ll see in our calculations below, these fuels release a lot of carbon when burned. The downside of burning a fuel for CO2 is that they produce not only CO2 but water vapor and heat that the grower has to deal with.
2) Release CO2 from a tank at a given rate using a regulator.
Releasing pure bottled CO2 is a simple method. Surprisingly, pure CO2 contains less carbon than either of the fuels (propane and natural gas) does, so this can be less cost-effective. An advantage of using pure CO2 is that it doesn’t produce water vapor and heat like fuels.
3) Use a decomposition process.
This is often done with fungi and detritus bags. This method tends to be more costly due to shipping, and could possibly raise issues with compliance, but can produce a good deal of CO2 depending on the product being used. Growers interested in this technique should look at product specs and pricing to determine if it’s cost-effective.
Growers have experimented with other CO2 supplementation methods like using dry ice or fermentation, but these three have been found most cost effective and are the most popular methods today.