Against an aromatic structure for soil fulvic acid

Abstract

Soil organic matter is by far the most abundant form of organic matter at the Earth's surface, playing an essential role in soil fertility by maintaining a favourable soil structure, by its water-retention properties and by its ability to store and release fertilizer elements, both cationic and anionic. Yet the nature and origin of its distinctive constituents, the humic substances, remain unknown. These dark-coloured acidic unsaturated compounds are generally considered to be predominantly aromatic and phenolic in character^1–3, largely on the basis of the high yields of benzene and hydroxybenzene polycarboxylic acids obtained, using various oxidation procedures, by Schnitzer et al.¹. Here we present evidence, at least for the water-soluble fulvic acids, that these aromatic and associated aliphatic oxidation products are possibly, sometimes certainly, artefacts or contaminants introduced by the complex chemical procedures involved in their isolation and identification.