Agriculture Reference
In-Depth Information
2.2
Water in soils
The amounts of water in soils and the forms and tenacity with which it is held are
the major determinants of rates and directions of soil processes at all spatial‚ temporal
and functional scales. This includes soil biological activity and most of the chemical and
physico-chemical processes occurring in the soil system.
The water molecule is not symmetric (Figure I.24). Two hydrogen ions with a fixed
angle (104.5°) between them occur at one end of the molecule inducing a positive charge
at this end of the molecule and a corresponding negative charge at its other end.
This polarity allows the formation of electrostatic bonds with other water molecules‚
cations in the soil solution and the predominantly negatively-charged surfaces of clays
and other surfaces. Water molecules do not act independently but are linked to sur-
rounding water molecules to form short-lived‚ two and three dimensional polymer-like
associations. They are also attracted to positively charged cations to form hydration
shells around them (Figure I.24).
