No such thing as humus?

January 31, 2012 – 5:39 pm

My soil nerd friends on Facebook have been linking this nice article from Science News discussing the importance of soils to global carbon among other topics. It has lots of good quotes and explanations by cutting-edge groups. One of the most interesting parts is the suggestion that there is no such thing as humus:

One old idea in particular is now in question, with the challenge culminating in a recent report in the journal Nature. Under fire is the belief that soil remains stubbornly soil, a large fraction of its organic materials resistant to decay because of the accumulation of large molecules called humic substances. One professional society devoted to the substances is in the odd position of hearing colleagues label as fiction its primary topic of study.

The idea presented in the article is that it doesn’t make sense energetically that these large resistant molecules will form in soils and that instead compounds as simple as sugars may be preserved in soils through other mechanisms. I did see a lot of talks at AGU in December about the importance of physical occlusion and other forms of stabilization in soils. I think as people continue to bring fancier methods from analytical chemistry (mass spec, HPLC, fluorometry, etc) to bear on these questions, we will in fact have to redefine what soil organic matter is chemically. However, it may be too soon to say that there is no such thing as chemical resistance to decomposition.

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