Hormone-like activity of the soil organic matter

Over the years, the physicochemical and biological properties of humic substances (HS) continue to attract the interest of researchers. HS which are heterogeneous organic compounds, influence the biogeochemistry of organic carbon in the global ecosystem. Among the properties of HS, their biological activity is of great interest. The reported evidences showed that the effects of HS on plant growth might depend on their source, concentration, molecular size, and on compounds contained into them. It is not known whether this activity is due to the chemical structure of HS or whether it is linked to hormones of microbial origin such as indole acetic acid entrapped into them. In any case, HS exhibit stimulatory effects on plant cell growth and development.