Let’s Get Geeky - Talking about Carbon : Nitrogen Ratios

After struggling with veggie growth in the plant based compost raised beds, I sent the 2 compost samples for KState soil analysis. And here are the results...

Manure Compost - Nitrogen 369.7 ppm

Plant Compost - Nitrogen 6.4 ppm

There is a WHOLE LOT that I don’t know about farming and composting. So forgive me if this is already common knowledge to many of you.

I’m going to geek out for a minute and talk about why I think this happened. And it has to do with carbon to nitrogen ratios (C:N). There is also a factor of available versus unavailable nitrogen but I’m still teasing that out. I’m kind of a slow learner.

All of the data and examples below are taken from the NRCS.

• Soil microorganisms need a C:N ratio of about 24:1 in order to survive. They eat 24 units of carbon and 1 unit of nitrogen for body maintenance and energy.

• Alfalfa hay (mature) has a C:N ratio of 25:1. Microbes eat it up quickly and leave no excess nitrogen behind.

• Wheat straw has a C:N ratio of 80:1. Microbes eat up 24:1 but leave a bunch of carbon left over. It takes longer to break down because the microbes have to search for (and use up) other nitrogen they can find in the soil in order to break it down. This leads to a nitrogen deficit.

• Hairy Vetch has a C:N ratio of 11:1. Microbes eat up the 11 units of carbon super fast, search for more carbon, and leave excess nitrogen in the soil for plant growth.

• Cow manure has a C:N ratio of 17:1, similar to hairy vetch. And this is the beauty of livestock.

I will be making changes to our raised beds to provide more nitrogen and to help build back up the microbes within the soil to help break it all down.