biofertilizers-biological nitrogen fixation, Phosphiobacterial inoculants , Mycorrhizal inoculants

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                                                                  Biofertilizers


Biofertilizers are carrier based preparations containing beneficial micro organisms in a viable state intended for seed or soil application and designed to improve soil fertility and help plant growth by increasing the number and biological activity of desired micro organisms in the root environment. They are supplement t chemical fertilizers and comparatively cheap. Biofertilizers are otherwise called as 'microbial inoculants'. The following microbial inoculants are being used to increase the growth and production of horticultural crops.



(i) Inoculants of biological nitrogen fixing micro organisms

(ii) Phosphiobacterial inoculants and 

(iii) Mycorrhizal inoculants

Biological Nitrogen Fixation:

Fixation of atmospheric nitrogen is effectively carried out by specific group of micro organisms either in free living condition (e.g. Azotobacter) or in symbiotic association with leguminous (c.g. Rhizobium) and non-leguminous (c.g. Azospirillum) plant systems. These micro organisms function at the prevailing atmospheric temperature and pressure.

The above microbial inoculants viz., Azotobacter inoculant, Azospirillum inocuiant and Rhizobium inoculants are available as carrier based (Peat soil based or lignite based) inoculants for different horticultural crops. The different methods of application of the above biofertilizers include (i) seed treatment or seed inoculation (ii) soil application or soil broadcasting and (iii) seedling dip or root bacterization in the case of transplanting vegetables to derive maximum benefits. By the above biofertilizer application, the fertilizer nitrogen can be reduced to the tune of 20 to 25%.


Phosphobacterial Inoculants:
Some free living bacteria in soil belonging to the genera Bacillus and Pseudomonas and fungi belonging to the genera Penicillium and Aspergillus possess the ability to bring insoluble phosphates in soil into soluble forms by secreting organic acids. The phosphobacteria are also known to mineralize the organic phosphates through enzymatic actions. Pre-treatment of the vegetable and other horticultural seeds with phosphobacteria has been reported to help in reducing phosphate fertilizer requirements of the crops and increasing the yield.

Mycorrhizal Inoculants:

Most of the horticultural plants have their roots colonized by soil inhabiting mycorrhizal fungi. These fungi known as Vascular Arbuscular mycorrhizal
fungi (fungi VAM) live in plant roots and grow out into the soil and increase the uptake of soil nutrients of low diffusion, particularly phosphorus and also increase the uptake of water. Invariably VAM fungi stimulate plant growth through increase in P inflow into the host plant. Experiments have confirmed that the VA-mycorrhiza enhances phosphate uptake through physical extension of the root absorbing surface rather than by induced changes in root physiology or by chemical solubilization of insoluble soil phosphate.

However, the VAM inoculum is available as soil + root based inoculum since the culturing of the fungus is not possible under laboratory condition. Experimental evidences proved the role of VAM inoculation in bhendi, gourds, chillies, egg plant, sweet potato by increasing the growth and yield. VAM inoculation induces better growth and more stem thickness in acid lime facilitating early production of pre-immunized acid lime seedlings.

Thus, biofertilizers bring lot of benefits to the farming community by way of economizing fertilizers and thereby reducing the cost of cultivation besides improving nutrient status of the crop plants and improving soil fertility etc.

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