I'm compiling some critical parameters for soil specifications for my wife, and unfortunately I come from a different industry (food safety, post-gate). I'm trying to read a set of lab analysis results for C:N Ratio and I cannot understand for the life of me:

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Are these listed as decimals? Or just notated with period as the ratio delimitator? If it's the latter, what is the significance in listing, e.g., 31:31 rather than 1:1?

  • When I say it, I interpret as % (so 33.37 -> ratio 1: 3337). But I have no definitive answer, and maybe I was wrong Commented Dec 2, 2020 at 10:59

1 Answer 1


It usually means the ratio of carbon to nitrogen, by weight.

So 33.37 means the carbon in the sample weighs 33.37 times as much as the nitrogen.

Nitrogen is essential for plant growth but, as your table shows, the amount of nitrogen in plant material is small, typically about 1%. On the other hand cellulose, the main chemical component of woody plant material, is about 45% carbon by weight and contains no nitrogen at all.

  • Why the "usually"? I find the absence of specificity in this specification sheet quite bewildering.
    – Arctiic
    Commented Dec 4, 2020 at 5:21
  • I can't imagine any use for the number, what is it for ? Commented Dec 4, 2020 at 15:51
  • @blacksmith37 Sorry didn’t get notification for some reason. Here’s a resource on that, USDA also has one but I’m on my phone at the moment.
    – Arctiic
    Commented Dec 16, 2020 at 7:59
  • @alephzero Not to imply any doubt on your part, but because it sounds like this isn’t a “for certain” type of answer I’m sort of just waiting on some additional corroboration before I mark your answer.
    – Arctiic
    Commented Dec 16, 2020 at 8:07

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