Types of biofertilizers
A. Azospirilium:
- It is wide spread in soil and plant roots. Tropical grass such as Digitaria, Panicum, Brachiaria, corn, sorghum, wheat, rye, barley, rice, millet and so on, whose cortical cells and protoxylem vessels contain Azospirilium.
Plant species
- Finger millet, sorghum: Azospirilium brasilense
- Rice, corm, setaria, Cyanodon dactylon, Amaranthus spinosus: Azospirillum lipoferum
- Inoculants carriers are: FYM, FYM + soil= all sterilized
Advantages
➢ 10 – 15 % increase yield due to N fixation [20-30 kg N/hectare/year].
➢ Production of growth promoting substance (auxins, gibberellins and cytokinin)
➢ Aggregate formation, colonizes the rhizosphere of numerous crop plants
➢ Azospirillum brasilense acts as biocontrol
➢ Renders plant drought tolerant when irrigation or rainfall is delayed in rice field.
B. Azotobacter
- Azotobacter is free-living, aerobic, non-symbiotic nitrogen-fixing bacteria and has been found beneficial to a wide array of crops covering cereals (corn, sorghum, wheat, rye, barley, rice) millets, vegetables, tropical grass such as Digitaria, Panicum, Brachiaria, cotton and sugarcane.
- These bacteria utilize atmospheric nitrogen gas for their cell protein synthesis. This cell protein is then mineralised in soil after the death of Azotobacter cells thereby contributing towards the nitrogen availability of the crop plants.
- It is wide spread in soil and plant roots.
Azotobacter chrococcum; Azotobacter paspali; Azotobacter beijerinckii – soil inhabitant
Azotobacter vinelardi – soil and water inhabitants
➢ Triple action of nitrogen fixation, bio-control, and production of plant growth promoting substances; e.g; Seed inoculants in wheat, tomato, rice, brinjal, cabbage, onion enhances yield increases due to the propagation of growth substances, antifungal, antibiotics and fixation of atmospheric nitrogen.
➢ Requires a large amount of organic carbon for its growth but are tolerant to high salts.
➢ Fix 15-20 kg/ha N per year
➢ Also increase germination and vigor in young plants.
C. Blue green algae (BGA):
- Blue green algae (BGA) are photosynthetic prokaryotic, simplest, living autotrophic (organisms capable of building up food materials from inorganic matter) micro-organisms.
- Blue Green Algae (BGA) or Cyanobacteria have the ability to carry out both photosynthesis as well as nitrogen fixation.
- They belong to the order Nostocales and Stigonematales.
The standing water of rice field encourages the growth of Blue Green Algae (BGA). These different species of BGA are:
- Anabaena
- Aulosira
- Nostoc
- Tolypothrix
- Haplosiphon
- Others
Advantages:
➢ Carry out both photosynthesis as well as nitrogen fixation (20-30 kg/ha/year). Add organic matter.
➢ Antifungal, insecticidal, nematocidal, cytotoxic.
➢ Anabaena azollae is nitrogen fixing symbiotic habitant of a tiny water fern azolla.
➢ Besides they excrete vitamin B12, auxins, AA and ascorbic acid increase available phosphorus in the soil.
➢ Increase WHC, aggregation, Permeability and exchangeable Ca.
➢ reclamation of Saline-alkali soils
➢ Release oxygen for the paddy roots, Converts Fe++ to Fe+++.
➢ Effective only in submergence rice and demands bright sunshine
➢ Algal mat in paddy fields also protects loss of moisture from the soil.
D. Azolla/ Azolla-BGA (Anabaena azollae) symbiosis:
- It is also called live floating N factory using energy from photosynthesis to fix atmospheric nitrogen. The most important biofertilizer of flooded rice is azolla and Blue Green Algae (BGA).
- Azolla is a floating fern which harbours blue green algae in its leaf cavities.
- The host plant (Azolla) provides carbon sources while Anabaena azollae fixes atmospheric N and transfers it to azolla which in turns multiply rapidly and this rapid multiplication creates a
- huge amount of biomass on the surface of the water.
- It is then harvested, dryed and used as biofertilizer.
- Azolla is decomposed very quickly and its N is used by rice very efficiently. It fixes about 40-80 Kg N/ha symbiotically with Anabena azollae.
- There are six species of Azolla-A. caroliniana, A. nilotica, A. mexicana, A. filiculoides, A. microphylla and A. pinnata.