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Moscow UniversitySoil Science BulletinVol.50. No.2, pp.45-52. 1995
Vestnik MoskovskogoUniversiteta. Pochvovedenie
UDC 631.16:576.8
SOIL BIOLOGY
ON THEORETICAL SUBSTANTIATION OF THE USE
OF MICROBIAL FERTILIZERS
P. A. Kozhevin and S. S. Korchmaru
Poss ib le r e s t r i c t i on s i n he r en t i n ob t a in i ng s t ab l e pos i t i v e e f fec ts f rom conv en-
t i ona l bac t e r i a l f e r t i l i zer s were cons ide red . T h e use o f a na tu ra l mic ro b i a l com-
plex ex t r ac te d f r om a fer t i l e soi l by phy s ica l m e t h o d s was sug ge s t ed as an a l te r -
na t i ve . E x pe r i me n t a l p roo f o f t he va l i d i t y o f t h e p r op os ed so lu t i on a r e p ro v id ed .
The year 1897 can be regarded as an initial stage in the history of the application of microbial fertilizers.
After Beijerinck succeeded in isolating a pure culture of nodule bacteria, Nobbe and Hiltner produced and
put on sale Nitragin , a pr od uc t conta ining nod ule bacter ia. Pa rad ox ica l as it is, mi crobial fertilizers were used
in many countries long before the world of micro orga nisms ha d b een discov ered; thes e fertilizers were applied
as the earth taken fro m und er legumes on soils wit h low yield of leg umi nou s crops. Along wi th Nitragin,
products based on cultures of various bacteria were broadly advertized (as Alinite containing putrifactive
bact eria) . Microbial fertilizers were tou ted as th e gre ate st discove ry of th e 20t h cent ury to boo st crop
yields. The use of bacterial fertilizers dates back to 1911, when Bacteriological and Agricultural Station in
Moscow and Agricultura l an d Bacteriological Lab orat ory in St. P ete rsb urg sta rt ed prod ucing Nitragin. By
that time it became obvious that microbial fertilizers were far from being always efficient (Rudakov et al.,1938).
No serious analysis of rest rict ions an d failures ha d been ca rrie d out, due to th e absen ce of reliable
methods of identification and enume ratio n of microbial popul atio ns u nde r nat ur al conditions, on one hand,
and a trend towards the search for new microorganisms with a higher efficiency, on the other. This approach
broadened the scope of microorganisms which could be of interest from the viewpoint of the efficiency of
their agricultural use (Lyn ch, 1 987). Currently , pro mising res ults obt ai ne d in th e field of gene engineering
regarding the possibilities of the development of new microorganisms to make a revolution in agriculture
aroused deep interest amon g th e speciali sts. Th e only imp edi men t could be th e necessity of th e analysis of
adverse implications (Tiedje et al., 1989). Th e prob lem rel ated to t he esti mat ion of possible risks has not
been solved so far (Kozhevin, 1994; Zvyagintsev, Kozhevin, 1994); however, this most obvious (though far
from being the only one) restriction does not prevent the emergence of promising genetic projects.
History develops in a spiral making geneticists think of expectations which were engulfing people at
the tur n of the century. Despi te considerable endeavors being mad e by a great nu mbe r of researcher s, the
problem related to t he use of microb ial fertilizers is still far from b ein g solved. Therefo re, ne arly 100 years
after the beginning of the use of microbial fertilizers to increase crop yield, quite urgent would be an attempt
at ecological analysis of the problem with possible potentialities and restrictions to be revealed.
The very history of the application of microorganisms as fertilizers showed that similar effects were
recorded in using diverse pop ula tion s with varying biological an d technological pot entia ls. In this respect,
quite reasonable would be a tren d towards studie s of a group of "p lan t growth stimu lato rs" comprising
not only nitrogen fixers (as nodule bacteria, azotobacter, azospirillum), mycorrhiza, and other microorgan-
isms providing plants with phosphorus, nitrogen, and other elements, but also microorganisms forcing out
undesirable populations with phytopathogenic and phytotoxic effect from the rhizosphere (Shippers et al.,
1995 by Allerton Press. Inc.
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Basing on the information available doubts may arise as to the usefulness of microbial fertilizers, the
more so, as yield increments are not always statistically significant and usually do not exceed 15%.However,
in our opinion, the potentials of microbial fertilizers are far from being exhausted. The doubing of the yieldin some cases may serve as a proof of this assertion. The main problem to be solved is instability of effects
and relevant restrictions.
The search and development of new microorganisms with a high level of useful characteristics using
gene engineering technique is very important, but they have certain restrictions researchers should be aware
of. Hopes for successful solution of all problems of introduction using genetic methods are not justified. B
analogy one can speak of an unfeasible design of an aircraft which could be the fastest, the lightest, having
the highest carrying capacity, reaching the highest altitude, being the most reliable and cheapest. A real
design will always be a compromise due to existing restrictions, with the final combination of characteristics
of even relatively simple designs to become clear only after testing.
With the entire diversity of concept of ecological strategies of microorganisms being the case, the mainidea is that a population cannot maximize simultaneously parameters related to r- and K-selection due
the principle of preservation (limited elasticity) (Kozhevin, 1980). An introduction of additional geneticinformation into a cell will inevitably have an effect on the ecological strategy; in some cases it will decreaseits competitiveness (e.g., plasmid as an intracell parasite in connection with additional expenditures forbiosynthesis), in other cases, may increase the risk of undesirable implications (Kozhevin, 1992).
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