As more cover crops are adopted across the county and soil health comes more into focus, we need to spend a little time understanding and examining carbon-to-nitrogen ratios, C:N.

Carbon is likely the least talked about nutrient when it comes to crop production, and outside of soil health discussions is often taken for granted.

Carbon is the building block for life, a key component in all life forms — and having a balanced carbon diet produces a healthy organism.

In soil, the microbes that decompose plant material, convert commercial fertilizers to plant available nutrients and build organic matter have a specific C:N ratio; 8:1 and proper crop residue decomposition occurs around 24:1.

These organisms need about 16 parts carbon for energy and eight parts for maintenance, which equates to 24:1.

Why is any of this important? Whenever we have a crop that is low in carbon legumes — for example, fresh cut grass — we have a lower carbon number, so these crops are consumed faster because the bugs need to eat more of them to achieve their balanced diet of 24:1.

The result of all this extra consumption is waste in the form of plant available nitrogen. On the contrary, when we have a crop like oat straw or corn stover, we have a very high C:N ratio, nearly 80:1, so the microbes have a hard time breaking this down, and in doing so they steal nitrogen from the soil to balance their diet.

For example, when we plant corn back to back, we may need to increase our nitrogen application the second year because the typical amount applied for a growing corn crop will be tied up by the microbes to aid in breaking down the previous year’s residue and essentially starving the current crop.

On a side note, that’s why pre-sidedress nitrate and leaf tissue tests are an important part of a fertilizer program, so we can account for earlier applied nitrogen that may not be taken up by the corn crop impacting yield.

The point of this column isn’t to turn everyone into a microbiologist, but rather to raise awareness of a lesser discussed topic.

Depending on where you live in the country can dictate how important the C:N ratio really is. If you live in the arid conditions of dryland farming on the plains, where you may only see 16 inches of rain in a good year, planting covers high in carbon are a great way to armor the soil and hold moisture.

On the other hand, living in an area like ours with good rainfall and steeper slopes, planting a field of brassica wouldn’t be beneficial since they would decompose so quickly. We wouldn’t be able to protect the soil at all.

Just as we benefit from a balanced diet, microbes do the same way and when developing your own mix, the C:N ratio is something we want to be aware of. Some cover crop calculators provide the ratio of the mix, so you can adjust species selection to achieve a desired result.

Some good rules of thumb as you’re planting covers: you want to keep faster covers, succulent legumes in front of nitrogen loving crops; you want soil armoring covers, rye and other mature small grains in front of nitrogen fixers; soybeans, since the nitrogen-starved environment actually increases the fixation on the bean crop.

Soil health isn’t an exact science, but there is a bit of chemistry and biology that go into it. Having a good understanding of the C:N ratio can go a long way into creating a healthy soil environment and increasing the overall profitability of the farm.

Andy Gaver is a conservationist with the USDA Natural Resources Conservation Service in Butler County.