Hmmm… What is Humus Anyway?

Just a tasty chocolate superpower or some strange concoction of randomized order generated from chaos breakdown fractalizing in its tumbling freefall?

I feel like when I try to look for research articles relating to the biochemistry of humus formation, I find many studies from earlier last century, less from recent years, though they do exist. It feels like there’s a bit of a drop off after the 1970’s on this type of work, I had read somewhere once that this happened because agriculturalists chose to focus more on soil chemistry and let go of their interests in soil organic matter, so there’s a bit of a drought on humus ecology.

A paper by Manlay and Swift (2007) characterizes humus / soil organic matter (SOM) as a cultural concept with three phases of perception, shifting from a more tradition humus-oriented practice to a mineral perspective heavily influenced by Josef Liebig, and in more recent decades emerging as a key indicator for soil health and quality, including agroecological health and fertility.

Humus is a complex substance that is not well understood. It still remains a bit of a mystery. The composition is generally described as consisting of “humins”, which are solid complexes, along with humic and fulvic acids which may be soluble, and other water-soluble compounds.

It’s the dark chocolate cake left behind after all the fresh leaves and apple stems have fully decomposed. Organic matter is feasted upon by primary decomposers, bacteria and fungi, including actinobacteria, and secondary and tertiary decomposers in the soil food web, like protozoa and nematodes, facilitate the transformation of organic matter into plant available nutrients and beneficial enzymes, which is described as the process of “mineralization”.

While much organic matter goes into the mineralization process of nutrient cycling, some of it goes into humus formation (humification), a means of long-term carbon storage. It is thought that the breakdown of lignin is the primary source of humification, which is often facilitated by fungi, such as white-rot and brown-rot fungi, as well as actinobacteria. Ultimately these lignin breakdown products undergo a self-condensation, or sugar-amine condensation. As FJ Stevenson describes it, there are an “astronomical” number of potential combinations that the compounds could come together, so every humus complex is different.

Those fungi keep showing off their carbon sequestration skills. They may be more efficient than bacteria at sequestering carbon into their bodies (Six et al, 2006), and are also important to the lignin degradation process of humus formation.

In terms of practices, this means that greater abundances of soil fungi are going to support enhanced carbon sequestration and the build up of long-term storage pools of carbon in soil. So, less disturbances, more quality fungal foods like woody materials. Less tillage, more mulch. More trees. Integrated cultivation systems. Trees, shrubs, herbs, animals, berries, vegetables, compost.

error

Leave a Reply

Your email address will not be published. Required fields are marked *