Thus,
these microorganisms help to provide a
vital source of oxygen to plant roots.
Reduced compounds such as meth-
ane and hydrogen sulfide are often pro-
duced when organic materials are decom-
posed under anaerobic conditions. These
compounds are toxic and can greatly sup-
press the activities of nitrogen-fixing mi-
croorganisms. However, if synthetic mi-
croorganisms, such as photosynthetic
bacteria that utilize reduced substances,
are present in the soil, oxygen deficien-
cies are not likely to occur. Thus, nitro-
gen-fixing microorganisms, coexisting in
the soil with photosynthetic bacteria, can
function effectively in fixing atmospheric
nitrogen even under anaerobic conditions.
Photosynthetic bacteria not only per-
form photosynthesis but can also fix ni-
trogen. Moreover, it has been shown that,
when they coexist in soil with species of
Azotobacter, their ability to fix nitrogen is
enhanced. This then is an example of a
synthetic soil. It also suggests that by rec-
ognizing the role, function, and mutual
compatibility of these two bacteria and
utilizing them effectively to their full po-
tential, soils can be induced to a greater
synthetic capacity. Perhaps the most effec-
tive synthetic soil system results from the
enhancement of zymogenic and synthetic
microorganisms; this allows fermentation
to become dominant over putrefaction and
useful synthetic processes to proceed.
Classification of Soils