Microbial inoculants or Biofertilizer are an important components of organic farming, which help to nourish
the crops through required nutrients. These microbes help to fix atmospheric nitrogen, solubilize and
mobilize phosphorus, translocate minor elements like zinc, copper, etc., to the plants, produce plant
growth promoting hormones, vitamins and amino acids and control plant pathogenic fungi, thus helping to
improve the soil health and increase crop production. Biofertilizers like Rhizabium, azotobacter,
Azospirillum and blue green algae (BGA) are in use since long. These organisms fix atmospheric nitrogen
and supply it to plants. Hence, bio fertilizers to some extent. The bacterial biofertilizers contribute 20-30 kg
N/ha/season. Rhizobium inoculant is used for leguminous crops. Azotobacter can be used with crops like
wheat, maize, mustard, cotton, potato and other vegetable crops. Azospirillum inoculants are
recommended mainly for sorghum, millets, maize, sugarcane and wheat. Blue green algae belonging to
genera Nostoc, Anabaena, tolypothrix and Aulosira fix atmospheric nitrogen and are used as inoculants for
paddy crop grown both under upland and low land conditions. However, the inoculants are most effective
under low land rice cultivation and contribute 20-30 kg N per ha per season with better quality of grains.
Anabaena in association with water fern Azolla contributes nitrogen up to 60 Kg/ha/season and also
enriches soils with organic matter.
Biofertilizer
Phosphate solubilizing microorganisms (PSM) are a group of microbes capable of solubilizing inorganic
phosphorus from insoluble sources. In alkaline and acidic soils, the availability to phosphorus is low.
These microbes can be useful to reverse this process. PSM when used with rock phosphate can save
about 50% of the crop requirement of phosphatic fertilizer like single super phosphate. Simple inoculation
of seeds with PSM gives crop yield responses equivalent to 30 kg P2O5/ha of phosphatic fertilizers.
Vesicular-Arbuscular Mycorrhizae (VAM) fungi are found to be associated with a majority of agricultural
crops. VAM occur over a wide range of habitats from aquatic to desert environments. VAM have been
associated with increased plant growth and enhanced accumulation of plant nutrients, mainly
phosphorus, zinc, copper and sulphur through greater soil exploitation by mycorrhizal hyphae. Maximum
root colonization and sporulation occurs in soils with low phosphorus. The results of field trails conducted
in India indicate that VAM inoculations increase yields significantly but the response varied with soil type,
soil fertility and VAM cultures. The major constraint for field application is the inability to produce ‘ clean
pure’ inoculum on a large scale as the fungi are obligate symbionts and have to be maintained and
multiplied on living host plants. In such a situation, until suitable technology is evolved to multiply these
fungi on a large scale, it is better to concentrate on crops normally grown in nurseries so that they can be
easily inoculated with selected strains and then transplanted.