Short Notes on Clay-Humus Complex

This article provides short notes on clay-humus complex.

It is evident that various clay minerals can bind humus substances through some linkages known as clay-humus complex. Many investigators consider that the complexes between humus substances and clays are probably formed by bridging through the exchangeable cations like Ca, Mg and Al. Besides this, they also consider that humus substances penetrate into the inter layer space of the crystalline clay mineral lattice.

Another mechanism for the formation of stable clay-humus complexes are associated with the help of sesquioxides, which make specific bridges between humus substances and the crystalline lattice of clay minerals.

Presumably these bridges are complex Al and Fe- humus compounds with non-siliqte forms of sesquioxides. They are fixed to the surface of the clay minerals during dehydration by a process of adhesion at the expense of inter molecular types of linkages.

There are two types of linkage take place during the interaction of clay with humic acids:

(i) Unstable-type of linkage, humic acid is arranged on the external micelle surface of the clay; this humic acid is easily extracted by alkali;

(ii) Stable-type of linkage, (humic acid is not extracted by alkali), is formed from the interaction of clay, humic acid and the exchangeable cations (Fe³⁺, Al³⁺, Ca²⁺ and Mg²⁺ occurring in the lattice of the clay mineral; the —OH and —COOH groups in the humic acid take part in the linkage.

The formation of clay-humus complexes has some practical implications for the establishment of soil structure and for fixing organic substances in the soil.