Types of Bio-fertilizers

A Nitrogen fixing bio-fertilizers

1. Symbiotic bacteria containing bio-fertilizer:

i) Rhizobium:

• It colonizes the roots of specific legumes to form tumour like growth, called root nodules.
• The Rhizobium legume association can fix up to 100-300 kg N per hectare in one crop season and in certain situation can leave behind substantial nitrogen for following crops.
• Important strains of R. bacteria are japonicum (better for soybean inoculation), R. meliloti (alfalfa), R. leguminosarum (peas), R. phaseoli (beans).

ii) Azolla:

• commonly seen in low land fields and shallow fresh water bodies.
• forms a green mat over water which often becomes reddish color due to the accumulation of anthocyanin pigments.
• The Azolla anabaena association is a live floating nitrogen factory using energy from photosynthesis to fix atmospheric N amounting to 100-150 kg /ha N from about 40-60 tonnes of bio-mass.
• Important strains of bacteria are caroliniana, A. nilotica, A. mexicana and A.

iii) Azospirillum:

• Azospirillum lipoferum has associative symbiosis with higher plant system.
• They don not produce any visible nodules on the root tissues.
• The crops, which respond to Azospirillium inoculation are maize, barley, oats sorghum, pearl millet and forage crops.
• Its application increases grain productivity of cereals by 5 -20% and fodders by over 50%.

2. Non-symbiotic:

i) Azotobacter:

• Application of Azotobacter has been found to increase the yield of wheat, rice, maize, pearl millet and sorghum upto 30% over control.
• Apart from N, this organism is also capable of producing antibacterial and anti fungal compounds, hormones and siderophores.

ii) Blue green algae (BGA):

• BGA are referred to as paddy organism because of their abundance in the paddy fields.
• BGA anabaena azollae also occuers in symbiotic relation with the aquatic fern Azolla.
• On the farm level the algae can contribute to about 25-30 kg N/ha.
• Recent researches have shown that algae also help to reduce soil alkalinity and this opens up possibilities for bio-reclamation of such inhospitable environment.

B. Phosphate mobilizing biofertilizer

a) Phosphate absorber

i) Mycorrhizae or Vesicular Arbuscular Mycorrhiza (VAM):

• It is a symbiotic association of fungi with roots of vascular plants.
• The main advantages of micorrhizae to the host plants lies in the extension of the penetration zone of the root fungus system in the soil, facilitating and increase phosphorus uptake.
• The inner connected the network of external hyphae acts as an additional catchment and absorbing surface in the soil beyond the depletion zone that would otherwise be inaccessible to plant roots.
• Mycorrhizal fungi’s assists the uptake of phosphate and trace metals and possibly influence water and nutrient via hormonal influences is not in doubt.

b) Phosphate solubilizers

• A group of heterotopic microorganisms are known to have the ability to solubilize P from insoluble sources.
• Phosphate solubilizers are Pseudomonas spp, Bacillus megatherium, Aspergillus awamori, Pencillium digitum, Trichoderma spp , which are responsible to solubilize the phosphates in the soil.

C. Organic matter decomposer

a) Saprophytes

• Saprophytes are those microorganisms that feeds by absorbing dead organic matter. Most saprophytes are bacteria and fungi.
• Saprophytes are important in food chains as they bring about decay and release nutrients for plant growth.