Agriculture Reference
In-Depth Information
CHAPTER
2
SOIL BASICS II
M
ICROSCOPIC TO
A
TOMIC
O
RBITAL
D
ESCRIPTION OF
S
OIL
C
HEMICAL
C
HARACTERISTICS
In this chapter soil components will first be considered as individual inde-
pendent, noninteracting entities. Then the interaction between the various
components in soil will be discussed. However, it is essential to know
and remember that components in soil never act independently of each
other. In addition, surfaces always have a coating of some type that is not
continuous, varies in thickness, and sometimes exposes the underlying
surface. Sometimes this first coating will have another, different, coating on
top of it.
Before an understanding of the interactions between soil components and
surfaces is possible, it is essential to know the composition of uncoated soil
components. Once this is known, it is then possible to discern the interactions
and bonding patterns of these components with and without coatings.
The solid portion of soil is made up of sand, silt, clays, and organic matter.
Elements and inorganic and organic molecules and ions are also present. The
soil solution is a combination of elements and inorganic and organic ions and
molecules. The gaseous portion contains gases commonly found in the atmos-
phere. However, the concentrations of these gases are very different in soil air
than in the atmosphere. All components are subject to partitioning between
these three phases.
The chemistry of soil is contained in the chemistry of these phases, the
elements present, their bonding, and the atomic and molecular orbitals
available for bonding and reaction. For the solid phase the chemistry will
depend on the amount and type of surface available for reaction. In the liquid
phase solubility will be the most important characteristic determining the
chemistry occurring. In the gaseous phase gas solubility and the likelihood that
the component can be in the gaseous form (i.e., vapor pressure) will control
reactivity.
