Soil Colloids: Meaning and Types

After reading this article you will learn about the meaning and types of soil colloids.

Meaning Soil Colloids:

The colloidal state refers to a two-phase system in which one material (or materials) in a very finely divided state is dispersed through a second. Few examples of the colloidal state—milk and cheese; clouds and fog; starch, gelatin, rubber, proteins, blood, and soil etc.

The rapidly diffusing substances, mostly of crystalline nature in the solid state, are called crystalloids while starch and proteins are called colloids. But this distinction is not always true, because a crystalline substance like NaCl can be obtained in colloidal condition while albumin may be obtained by crystalline form.

It is, therefore, be more appropriate to speak of a over colloidal state of a substance than of a colloidal substance. The size of the particles in true solutions and in colloidal suspensions is 0.2-1 mp and 1-200 mp respectively. Colloidal particles float in a medium and do not tend to settle.

Therefore, colloids are referred to as dispersed systems. The substance in solution is called the dispersed phase while the medium in which the particles are dispersed is called the dispersion medium. Soil particles less than 0.001 mm size possess colloidal properties and are known as soil colloids.

Type of Soil Colloids:

Except sand fraction, all soils contain particles of colloidal size. Soil colloids are chemically active portion of the soil.

The individual crystalline particle is called “micelle” or “micro cell”. Colloidal clay particles are considered as occupying an intermediate position being neither truly lyophilic (liquid loving) or hydrophilic (water loving) nor lyophobic (liquid hating) or hydrophobic (water repellent). Clay colloids posses the properties of hydrophilic because of its hydration. Its sensitivity to electrolytes is a hydrophobic nature.

i. Lyophobic colloids:

The surface tension and viscosity of this colloidal system is similar to that of the dispersion medium. Small quantities of electrolytes cause precipitation. The particles are easily detected in ultra-microscope and they migrate in one direction in an electric field.

ii. Lyophilic colloids:

The surface tension is usually lower and the viscosity is much higher than that of the dispersion medium. Large quantities of electrolytes cause precipitation. The particles cannot be easily detected in ultra-microscope and they migrate in different directions or not at all in an electric field. Among all kinds of soil colloids, the silicate clays are the most dominant and important in the field of agriculture.