It didn’t matter only if an organism was present in soil, however.
If the question was the amount of nitrogen fixed in a given agricultural
or forest soil by its native microbial life and therefore
whether nitrogen fertilizer was needed and if so, how much,
Vinogradskii realized that pure culture methods were useless.
What one needed to know was: in the conditions that existed in
that soil in the field, how numerous and active were those bacteria,
and at what rate did they fix nitrogen. For his purposes, Vinogradskii
defined a new measure: the soil’s “microbiological state,”
i.e., its “quantity and quality of active microbial cells” (p. 112).
Interestingly, Ackert tells us (p. 111) that even agricultural experiment
stations had taken up Koch’s pure culture methods for
studying soil microbes. So Vinogradskii had to make the case for his
methods even in that setting. Always then he strove in his lab experiments
to find new ways to simulate natural conditions and
measure the physiological activity of his microbes in those conditions.
Ackert surveys the discussion of the “field vs lab” dichotomy
in history of biology and shows nicely that Vinogradskii effectively
bridged that divide, bringing “free nature into the laboratory” (p. #).
Recent studies that search for DNA sequences in soil and water are a
logical extension of the principle and methods he sought to
establish. And like Vinogradskii’s own work, these newer studies
remind us anew of how dramatically more complex life is in natural
environments, than in laboratory pure culture studies alone.