Environmental Engineering Reference
In-Depth Information
the mineral particles in soil. This is the
Emerson model
of structure formation and
illustrates that attraction between particles depends upon electrostatic forces on the
surfaces of colloids. These electrostatic forces are discussed on pp. 387-91. The role of
organic matter lies in providing a strong and stable structure, owing to the fact that the
humic colloid is
hydrophobic
, i.e. water-repellent. This means that the structural unit is
stable and is more likely to survive in the face of wetting and of raindrop impact. The
grade
or
stability
of structure is an important property in studies of soil erosion; usually
three grades of structure are recognized - weak, moderate and strong (Plate 18.1).
Figure 18.3
The arrangement of quartz particles, clay
domains and organic colloids in a soil aggregate.
Source: After Emerson (1959).
