Originally Posted by Tim Wilson
There is a school that considers humus a covalent bonded material and this is likely where the 'biomolecule' language comes from.
By humus you mean humic acids, fulvic acids, and humin? These comprise what can be considered the "classical definition" of humic substances based on solubility properties. I think you give the author of the statement far too much credit. He/she states humus (all inclusive) is a biomolecule, then mentions humic acid (a component of humus).
I will also point out these substances are more likely to form intermolecular bonds with each other rather than intramolecular bonds based on the research I have reviewed.
If there is a school of thought that demonstrates these substances can and do combine covalently (i.e. intramolecular bonds), beyond what has been suggested in limited research via inner-sphere complexes with some metal cations (Ca^2+), I would be most interested in seeing it.