Humic Substances, Part 2: Introduction

INTRODUCTION


Humic substances (HS) are the most widely-spread natural complexing ligands occurring in nature.
The presence of HS in soils have also been detected, even in the Antarctic continent where the
humification process under Antarctic conditions is very specific and different from the other continents (Gajdošová et al. 2001, Pacheco and


Havel 2002, Gajdošová et al. 2003). They make up the bulk of organic matter, because they represent
most of the organic materials of soil, peat, lignites, brown coals, sewage, natural waters and their sediments. Humic substances can be divided into three components: fulvic acids (FAs), humic acids (HAs) and humin. One of the most important parts of HS is HAs. Humic acids and FAs represent alkali-soluble humus fragments, humin represents the insoluble residue. Because of their molecular structure, they provide numerous benefits to crop production. They help break up clay and compacted soils, assist in transferring micronutrients from the soil to the plant, enhance water retention, increase seed germination rates and penetration, and stimulate the development of microflora populations in soils (Senesi et al. 1991).

The remarkable properties of humic acids have attracted the attention of many investigators. The results over the years have brought new knowledge on their structure and physicochemical properties and pointed to the use of these interesting natural compounds in many practical applications. The aim of this article is to review the current state of knowledge and to present current applications in agriculture, industry, the environment, and biomedicine (see, e.g. Ziechmann 1994).