Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

9.3.3. Nutrient absorption enhancers
Increasing the absorption of applied nutrients by
the plants, as opposed to the soil, is a means of
increasing fertilizer use efficiency. J.L. Anders and
L.S. Murphy (1997) presented work with a
polymer which shows improved nutrient uptake
and nutrient use efficiency.
9.3.4. Bio-fertilizers; microbial
inoculants
Microbial seed inoculants, commonly but wrongly
called bio-fertilizers, are able to enhance
biological nitrogen fixation or to solubilize soil
phosphate. The inocultants are claimed to be cost
effective, eco-friendly and renewable, and
generally capable of supplementing chemical
fertilizers in sustainable agricultural systems.
It has long been known that the inoculation of
efficient strains of the symbiotic Rhizobium can be
beneficial for leguminous pulses and oilseeds.
Free-living organisms such as Azobacter and
Azospirillum have proved effective for rice and
certain other crops. The problem with inoculants
is that establishment and therefore effectiveness
depend on the natural conditions and on the skill
of the user. As regards the product itself, the
inoculant is a living material and there are
problems due to the need to select the most
effective strains, the difficulty of quality control,
the short shelf-life, the need to avoid high
temperatures in storage etc.
As regards phosphate, several phosphate-
solubilizing bacteria are known to mobilize
significant quantities of soil phosphate that would
otherwise not be available to the plant, but their
effectiveness is variable and not predictable.
Vesicular-arbuscular mycorrhizae have
favourable effects on P uptake but much more
research and development is required before
reliable commercial products can be made
available. At present it is difficult to produce
mycorrhizae in bulk.
The Food and Fertilizer Technology Center
for the Asia and Pacific Region (FFTC, 1997)
report that, while there is an increasing interest in
Asia in the use of N-fixing and P-solubilizing
bacteria, the technology of producing and using
them is still at an early stage. While some are
very effective, farmers often find themselves
paying large sums for useless products. There is a
very large number of different microorganisms in
microbial products and they are often not
identified, whereas some are crop-specific. They
tend to be heavily promoted and there is a great
need for standards and for simple and accurate
ways of measuring their effectiveness.
In general, microbial inoculants have received
only limited acceptance by farmers in developing
countries. They show considerable promise but
more development is required. In general, it

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seems likely that, in due course, they will become
significant supplements to mineral fertilizers but
they cannot replace them.
A considerable amount of work has been
done on microbial inoculants in India. In 1996
there were 62 manufacturing units in the
country. The Fertiliser Association of India has
produced a booklet on the subject (FAI, 1994).