Introduction:
It is a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by enhancing the supply, availability, accessibility of several primary nutrients to the host plant.
Bacteria, fungi, and mycorrhizae, belonging to the Bacillus, Lactobacillus, Azotobacter, Pseudomonas, photosynthetic bacteria, Trichoderma sp., Glomus sp., Gigaspora sp., Pezizella sp., and yeasts, which are capable of fixing nitrogen, solubilizing phosphate, zinc, iron, potassium, and producing phytohormones and cellulolytic enzymes, are primarily used as biofertilizers.
Why bio fertilizers?
It’s a microbial green revolution. Bio fertilizers are having it sown advantages over chemical fertilizers and it is economically and environmentally friendly too. With the increasing demand in agriculture, it has become important for us to increase the productivity by using various fertilizers such as insecticides and pesticides. But with the excessive use of these products the soil has been affected seriously and the composition of the soil are also deteriorated because of the depletion in the essential minerals of the soil. So, in order to overcome this problem and issues it has become important globally to use a different remedy for the production of various bio fertilizers. They are the also best at economic value.
Types :
Bio-fertilizers are also classified into different types based on the type of microorganism they contain, including bacterial biofertilizers such as Rhizobium, Azospirillum, Azotobacter, and Phosphobacteria; fungal biofertilizers like Mycorrhiza; algal biofertilizers such as Blue Green Algae (BGA) and Azolla; and biofertilizers from actinomycetes. In general, it is also classified as:
- Nitrogen bio fertilizers
- Compost bio fertilizers
- Phosphorous bio fertilizers
Nitrogen fixing fertilizers
Symbiotic: Rhizobium
It belongs to rhizobiaceae family, the rhizobium bacteria present in the nodules of the plants, such as legumes like soybeans, peas, and alfalfa These bacteria fix atmospheric nitrogen into a form that plants can use for growth, which helps improve soil fertility without the need for synthetic nitrogen fertilizers.
Morphology:
- Unicellular, cell size less than 2µ wide. Short to medium rod, pleomorphic
- Motile with peritrichous flagella
- Gram negative
- Accumulate poly β-hydroxyl butyrate granules.
Fig: Bacteria in nitrogen cycle
Physiology:
- Nature: chemo heterotrophic, symbiotic with legume
- N source: fixed from atmosphere.
- Respiration: aerobic.
- Growth: fast (rhizobium), slow (Brady rhizobium)
Recommended for: Pulses, Black gram, green gram, chickpea, pea, lentil, cowpea, pigeon pea, Oil seeds, soybean, groundnut.
Non symbiotic
Azotobacter is another genus of nitrogen-fixing bacteria that play a significant role in agriculture. Azotobacter belongs to the family Azotobacteriaceae and is known for its ability to fix atmospheric nitrogen and make it available to plants.
Morphology
- Cell size: large cell with ovoid structure, size ranging from 2.0-7.0×1.0-2.5µ.
- Cell character: polymorphic
- Accumulate poly β-hydroxyl butyrate granules.
- Gram reaction: negative
Physiology:
- Nature: chemo heterotrophic, free living
- Carbon source: a variety of carbon source (mono, di and certain polysaccharide) organic acids.
- Nitrogen sources: Nitrogen through fixation, amino acid, NH4, NO3
- Respiration: aerobic
- Growth media: Ashby Jensen’s medium
- Recommended for: Rice, wheat, millets, other cereals, cotton, vegetable, sunflower, mustard, flowers and it is expected to increase the productivity by 20 to 30%
Azospirillium
It is another genus of nitrogen-fixing bacteria that provides various benefits to plants, particularly in the family Spirillaceae. They have been found to colonize the roots of several plants, including sorghum, bajra, and maize. They form associations with the roots, residing within the root tissues and sometimes forming rhizospheric communities that benefit the plant.
It significantly increases the growth, nutrient uptake, chlorophyll content and mycorrhyzal infection in root.
Morphology:
- Cell size: 1in diameter, curved rod, size and shape may vary.
- Accumulate: poly β-hydroxyl butyric acid.
- Gram reaction: negative
- Development of white pellicles 2-4mm below the surface of NFB medium.
Physiology:
- Nature: chemoheterotrophic, associative.
- Carbon source: L-arabinose, organic acid, D-gluconate, D-fructose, D-glucose, sucrose, pectin.
- Nitrogen sources: Nitrogen through fixation, amino acids, NH4, NO3
- Respiration: aerobic, micro aerobic.
- Growth media: N free bromothymol blue (NBF)
- Recommended for; Rice, millets maize, wheat, sorghum, sugarcane and co-inoculants for legumes and it is reported that the average increase in yield 15-30%.
Phosphate solubilizing bio fertilizer
Phosphorus (P) always remains as one of the most important and critical plant macronutrients for the optimum growth of plants particularly in tropical areas,
However, soil possesses total P in the form of organic and inorganic compounds, most of them are in inactive and thus unavailable to plants. In this scenario, Phosphate solubilizing microbes (PSMs) are a type of beneficial and the efficient strain of bacteria, fungi, yeast and actinomycetes that can hydrolyse organic and inorganic insoluble phosphorus compounds into soluble P form, which plants may easily absorb. PSM provides an environmentally friendly and economically sound solution to alleviate P scarcity and subsequent plant uptake. Eg. Bacillus spp., Paenibacillus spp., Pseudomonas spp. etc.
Compost Biofertilizers:
Compost is a decomposing, brittle, murky material forming a symbiotic food web within the soil, which contains about 2% (w/w) of nitrogen, phosphorus, and potassium, along with microorganisms, earthworms, and dung beetles.
It is produced from a wide variety of materials like straw, leaves, cattle shed bedding, fruit and vegetable wastes, biogas plant slurry, industrial wastes, city garbage, sewage sludge, factory waste, etc., by different decomposing microorganisms like Trichoderma viridae, Aspergillus niger, A. terreus, Bacillus spp., several Gram-negative bacteria (Pseudomonas, Serratia, Klebsiella, and Enterobacter).
Applications:
- Soil Treatment
- Improving soil structure
- Maintain soil fertility and promotes a balanced nutrient cycling in the agroecosystem.
- Environmental sustainability
- Reduced Environmental Impact
- Some biofertilizers have biocontrol properties, suppressing soil-borne pathogens and pests.