Growers Need to Know About Carbon and Nitrogen Ratios

Paying attention to, and understanding, the ratio will allow growers to drastically improve results and to avoid potentially catastrophic nutrient burns.

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This story originally appeared on Marijuana Venture

Despite nitrogen being well–known and highly valued for its role in crop productivity, it has a subtle yet profound relationship to carbon that is almost entirely overlooked in the context of terpene farming. This relationship provides the basis for so much of what we understand about plants, how they grow and what kind of compounds they produce.

It also extends beyond just plants; this relationship is the interface between gases in the atmosphere and nutrients in the soil, so it also defines soil chemistry and microbiological activity.

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What’s this relationship we’re talking about? To put it simply, it is the ratio between carbon and nitrogen.

The concept is easy to understand at a high level: In order for nitrogen to be useful to plants, it must be attached to carbon. That’s essentially what amino acids are — nitrogen plus carbon. The specific pathways and chemistries involved in the biosynthesis of each amino acid are not as important as understanding that carbon traps nitrogen and keeps it in a form that is useful for plants. Without carbon in the system, nitrogen is useless.

One of the most abundant enzymes on this planet, rubisco, is a massive nitrogen sink for plants — in some cases, it can make up roughly 50 percent of the total protein content in plant leaves. By itself, this is impressive — but what does rubisco do?

Rubisco’s only job is to capture CO2 out of the air and convert it into a usable form for plants. That’s all it does. Connect the dots and you will see why this carbon-to-nitrogen ratio is so profound: Nitrogen is a tool that plants primarily use to capture more carbon out of the air, so that they can capture more nitrogen, so that they can capture more carbon, and on and on.

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In the context of terpene farming, nitrogen is one of the most important tools plants have to create more terpenes and cannabinoids, because the proteins made from that nitrogen are responsible for capturing the carbon that all terpenes and cannabinoids start off as. This carbon is then passed to other enzymes, which shape and mold it into more and more complex molecules. These compounds are predominantly carbon — monoterpenes are roughly 90 percent carbon by weight — and that carbon must first pass through an enzyme that requires nitrogen to perform its work.

The availability and quantity of one informs the other; the more carbon you give your plants, the more they can sink the nitrogen into an amino acid. This is why indoor commercial cultivators who run high levels of CO2 in flowering can also run higher fertilizer levels without burning their plants — the carbon creates a buffer that balances out the mineral load working its way up through the transpiration stream.

The effect of this is a very useful shield against over-fertilizing a plant, too. In a situation where the feedwater solution is too high for the carbon load placed on a plant, the best solution is often to simply raise the CO2 levels and the plant will balance the mineral load out against the carbon load. This can be done in a situation where a grower accidentally applied too much fertilizer and it’s too late for adjustments to be made, or the adjustments simply can’t be made.

Imagine having a sealed flowering room that was set at zero parts per million CO2. What would happen? This is no trick question: the plants would die, regardless of how much or how little mineral nutrition they receive. On the flipside, what if that room were set at 500 ppm CO2? Or 1,000? How about 2,000 or even 5,000? In order to keep up with the increased carbon load, the plants will eventually require additional minerals and additional water.

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Nitrogen is the gatekeeper which allows this great balancing act to occur on all pathways in plants. Paying attention to, and understanding, the carbon-to-nitrogen ratio will allow most growers to drastically improve their results and to avoid potentially catastrophic nutrient burns. It is no coincidence that this ratio has fascinated botanists and researchers for decades — it is easy to understand at face value yet there is a seemingly endless universe to explore. This is why understanding the carbon-to-nitrogen ratio also paves the way to understanding one of the fundamental pillars of all life on this planet.

The nuanced complexities of this ratio inform pretty much all biological processes at the moment when nitrogen gas in the air is fixed by microbes in the soil. They too play a delicate balancing act, as do the fungi in the soil and all the life working their way up to the top of the food chain … and back down into the ground again.

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