Agriculture Reference
In-Depth Information
Biochemical
and
Chemical
reactions
Organic
Matter
Pool
CO
2
+ H
2
O + Humus + E + Inorganic constituents
NC
Figure 3.1.
Organic matter (OM) breakdown in soil under aerobic conditions. These reactions
lead to the formation of humus and are carried out to release energy (
E
), which is used by micro-
organism. Heterotrophic microorganism use OM to construct new cells (NCs). They also lead to
a greater randomness in the system.
be associated with more complex organic materials, with humus, or with in-
organic carbon and clay as part of the soil matrix. These interactions can mask
the occurrence and concentration of both organic and inorganic components,
obscuring analysis and confusing analytical results.
SOIL BIOTA
3.1.
ANIMALS
Animals living in soil range from as large as ground hogs to as small as the
smallest insect and arthropod. However, for our purposes, when animals
become so small that a microscope is needed to see them, they are classified
as microorganisms. It is assumed that the main additions to soil from animals
are urine and feces. These are indeed common additions; however, all animals
add hair, skin and saliva, as well as the dead and decaying bodies of the organ-
isms themselves. In addition to biochemicals and bioorganic and organic
molecules, animals cause both large and small changes in the physical charac-
teristics of soil that can change its chemistry and the results of chemical and
instrumental analysis.
The effects of animals on the physical and chemical characteristics of soil
tend to be locally distributed in the sense that the holes are dug and urine and
feces and other waste products are deposited in localized areas. Animal holes
can lead to the movement of surface soil lower in the soil profile such that A
horizon material can be found in what would be expected to be a B horizon.
This occurs most often with the larger burrowing animals. With smaller
animals, material from lower levels in a soil may be brought to the surface
such as in the case of ants and termites. An ant colony and a grub found about
9 cm deep in soil is shown in Figure 3.2. In other cases, such as with worms,
soil may be intimately mixed with organic matter but not moved long dis-
tances. There are many different types of worms in soil, such as nematodes,
but only a few cause this important type of change.
