Q. What do you classify as high organic matter?
A. In my opinion, we shouldn’t be having a conversation about organic matter because it is too big and messy of a number — it means nothing.
Macro organic matter does not correspond in any way to microbial activity. There are a lot of different tests, but the one that I find corresponds most accurately to microbial activity is the Haney analysis — specifically its measurement of microbially active carbon. Microbially active carbon as defined on that analysis as the amino sugars and soil carbohydrates that biology can access.
This is a very important parameter to pay attention to if you have soils that are on either extreme end of the organic matter spectrum — very high organic matter or very low organic matter soils. Farmers growing in very sandy soils may think that their desired value for organic matter is 2 percent or 3 percent or 4 percent. But you can never reach even that on some Florida or Texas sands because the organic matter oxidizes too rapidly. Yet when we look at microbially active carbon, you can have very sandy soils in subtropical environments and high heat conditions that have very little total organic matter, but almost all of it is microbially active carbon. It’s cycling very quickly. You have abundant microbial communities.
On the opposite end of the spectrum, I’ve seen soils that were muck soils that had organic matter of 40 to 50 percent and microbially active carbon of next to zero, and they weren’t microbially active.
If we want adequate levels of calcium, silicone and boron delivered to plants from the soil, then the reality is that those nutrients aren’t going to be held very well in the soil simply as negative charges being held onto a positive holding site on an organic carbon molecule. Instead, they are successfully held inside the cells of microbes. That’s the key difference. They’re not held by the soil so much as inside fungi, algae, bacteria, protozoa, etc.
From John Kempf’s presentation at the 2024 Acres U.S.A. conference.
