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RE: Difference between Humus and Compost??? (Follow-Up #1)

posted by: robertz6 on 09.17.2011 at 05:03 pm in Soil Forum

The following I found by Googling 'Humus'; one hit directed me back to Gardenweb. I did not find the same when searching (this forum) and viewing the Soil FAQs. ???
Anyway, here is part of the post.

Organic matter - stuff that came from biological sources (should be biological matter. Diamonds and graphite don't decompose!) This includes humus, mature compost, immature compost, freshly cut plants, live plants, etc.

Humus - (soil science) that portion of the soil that has fully broken down and is thus stable. This stability is important because it allows you to remove it from consideration in a lot of investigations, and this is why soil sciences define it this way. This, incidentally, is also why its constituents have not been subjected to rigorous scientific investigation. It is not that it is somehow mysterious or has magical properties that elude investigation, it is just that it is only recently that anyone has really bothered to think about applying modern analytical techniques to this fraction of the soil. Contrary to common belief, a large number of its constituents ARE known. Their relative proportions vary from implementation to implementation, however, and thus no simple answer is really forthcoming as to "what humus is," as it is a dynamic mix of substances. humus - (colloquially) The organic portion of the soil (you can see how this definition has use for the gardener, but is too impercise for much usefulness in an investigation of soil properties.)

Compost - organic matter in a purposeful state of partial decomposition. The purposeful part is important. Dead stuff on the ground is NOT compost, just decaying orgainc matter. It is the controlled, or semi-controlled conditions that make it compost.


Compost involves the process of decomposition which provides nutrition for plants.

Humus is fully decomposed, inert, and provides soil structure and tilth.

Peat falls into the latter category.

clipped on: 09.19.2011 at 12:30 pm    last updated on: 09.19.2011 at 12:32 pm