Soil Carbon

Question 1

In the context of climate change, warmer temperatures generally decelerate carbon sequestration processes and accelerate carbon decomposition.

Question 3

Why was the traditional humus theory disproved?

Answer 3

1. The extraction is always incomplete, leaving 50%–70% of the organic carbon unextracted, which is then defined as the insoluble ‘humin’ fraction106.
2. The harsh alkaline treatment at pH 13 ionizes compounds that would never dissociate within the wider soil pH range (pH 3.5 to pH 8.5),
3. the development of this extraction method preceded
   theory, tempting scientists to develop explanations for the synthesis of materials resembling operationally extracted ‘humic substances’, rather than to develop an understanding of the nature of all organic matter in soil.

Question 4

What is the traditional humus theory?

Answer 4

Early research based on an extraction method assumed that a ‘humification’ process creates recalcitrant (resistant to decomposition) and large ‘humic substances’ to make up the majority of soil ‘humus’ (see Box 1).