Biofertilisers: Definition, Symbiotic Nitrogen Fixers, and Algal Biofertilisers, Phosphate Solubilising Microorganisms, Organic Fertilisers, Advantages and Limitation of Biofertilisers

Definition

Biofertilizers are organic fertilizers made of microbial inoculants of bacteria, fungi, and algae, either alone or in combination, which promote enhanced plant development through increased nutrient availability. Biofertilizers can be applied to soil, seed, or plant surfaces. Once within the plant, they colonize the rhizosphere and boost the host plant’s supply of essential nutrients. Through symbiotic or non-symbiotic associations, these microorganisms help plants in fixing Nitrogen from the atmosphere, solubilizing and mobilizing fixed Phosphorous, translocating minor elements like Zn and Cu, producing hormones that promote plant growth, vitamins, and amino acids, and controlling pathogenic fungi. Thus, it is expected that using biofertilizers will result in less use of chemical pesticides and fertilizers. In addition to microorganisms, biofertilizers also include organic fertilizers like Farmyard manure (FYM), which is produced by the rotting of agricultural waste. Utilizing biofertilizers is affordable and environmentally responsible. The natural world is full of these microbes. Utilizing biofertilizers increases crop output and decreases the need for artificial fertilizers, which improves soil texture and reduces other negative environmental effects. In actuality, the integrated nutrient management (INM) method advocates the use of both inorganic and organic/biofertilizers.

Biofertilizers are the following categories

1. Biological Nitrogen fixers, such as Rhizobium species for beans

2. Free-living, Non-Symbiotic Nitrogen fixers, such as Azotobacter and Azolla

3. Algae biofertilizers (using Azolla and blue-green algae (BGA))

4. Phosphate solubilizing bacteria (PSBs) 

5. Mycorrhiza

6. Organic Fertilizers

Algal Biofertilizers and Symbiotic Nitrogen Fixers

Bacteria like Rhizobium species demonstrate symbiotic interactions with host plants, particularly legumes. Agriculture has traditionally made use of cyanobacteria and blue-green algae (BGA). The bacterial biofertilizers fix at least 50–150 kg of nitrogen per hectare annually. Rhizobium and other root-nodulating bacteria are widespread. A few taxa develop stem nodules. For example, Azorhizobium species on Sesbania rostrata, create stem nodules. Based on the specific legume species that they nodulate, rhizobium is categorized. For example, R. Leguminosarum nodulates lentil (Lens culinaris), pea (Pisum sativum), and khesari (Lathyrus sativus); R. Phaseolus vulgaris and Phaseolus multiflorus generate nodules when exposed to phaseoli; R. meliloti nodulates fenugreek (Trifolium foenumgraecum) and lucerne (Medicago sativa); R. trifolium sp. nodulates clover, and R. white lupins are nodulated by lupini (Lupinus alba). Cyanobacteria, or BGA, are photosynthetic prokaryotic organisms that work with the Azolla freshwater fern to fix atmospheric nitrogen. The Genera Nostoc, Anabaena, Plectonema, Aulosira, and Tolypothrix are home to cyanobacteria. Both aerobic and lowland Azolla cultures are injected into paddy fields. However, under lowland conditions, where roughly 20–30 kg of Nitrogen is fixed per ha every crop season, the inoculum’s efficacy is higher. Cyanobacteria contain the enzyme nitrogenase, and specialized cells termed “heterocysts” are where Nitrogen is fixed. The nitrogenase is safeguarded against oxygen inactivation by these heterocysts, which also include the nif gene (engaged in N fixation). Anabaena is responsible for Azolla’s ability to fix nitrogen, and the fern provides food for the alga. BGA decomposition contributes to ecosystem biomass in addition to N fixation, improving the physical characteristics of the soil.

Free-living, Non-Symbiotic Nitrogen Fixers

The bacterial genera Azotobacter and Azospirillum fix atmospheric nitrogen. Crops including maize, wheat, mustard, cotton, potatoes, and other vegetable crops can be vaccinated with azotobacter. It fixes roughly 30 kg of nitrogen per hectare per year by using the organic matter in the soil. In particular, the cultivation of wheat, maize, sugarcane, millets, and sorghum is advised to use azospirillum inoculants.

Phosphate Solubilising Microorganisms

Microorganisms that can dissolve phosphate and liberate pi from insoluble sources increase the bioavailability of phosphate. The bacterial genera Thiobacillus, Bacillus, etc. contain these species. These microorganisms sometimes referred to as Phosphate Solubilizing Bacteria (PSBs), create compounds like pseudobactin, or “siderophores,” which chelate Fe. Because P is fixed as insoluble oxides, it is not readily available in both alkaline and acidic soils. When applied to soil or seed, the inoculants of PSBs can help mobilize fixed P. When used with PSBs, rock phosphate can cut the amount of phosphatic fertilizer needed by half. Crop yield responses from PSBs inoculation of seeds alone are equivalent to those from chemical fertilizer applications of 30 kg P2O5 per ha.

4. Mycorrhizae

Mycorrhizae, (mycor = fungi or rhiza roots), are close and mutually beneficial associations between a nonpathogenic or weakly pathogenic fungus and living plant root cells, particularly cortical and epidermal cells. The roots’ ability to absorb minerals and water is enhanced by the fungi after they obtain organic nutrients from the plant. Most plants that are grown on soil have mycorrhizal roots. All Gymnosperms, as well as about 83% of dicot and 79% of monocot plants, are mycorrhizal on a global scale. Young, delicate roots are typically affected because, in older sections, the cortex and epidermis are removed and cork cells form a protective layer of suberin. Mycorrhizae frequently have few such hairs because infection either slows down or stops the formation of root hairs. The absorbing surface area is significantly reduced due to the reduction in root hairs, but the long fungal hyphae that extend from mycorrhizae investigate more soil.

There are two primary types of mycorrhiza in nature

Ectomycorrhiza and Endomycorrhiza, Ectoendotrophic organisms, a rare group with intermediate characteristics, are additionally occasionally discovered.

Ectomycorrhiza: The fungal hyphae in ectomycorrhizae (ECM) create a mantle outside the root as well as inside the root in the intercellular gaps of the cortex and epidermis. Although there is no intracellular penetration into cortical or epidermal cells, a vast network known as the Hartig net forms between these cells. Ectomycorrhizae are typically found on the roots of trees, including those in the Pinaceae family (pine, fir, spruce, larch, and hemlock), Fagaceae family (oak, beech, and chestnut), Betulaceae family (birch, alder), Salicaceae family (willow, and poplar), and a few other families.

Endomycorrhiza: Fungi thrive in the intercellular gaps of endomycorrhiza and reside inside the cortical cells. Vesicular arbuscular mycorrhizae (VAM), the most prevalent subgroup of endomycorrhiza, ericoid, and orchidaceous mycorrhizae are the other two subgroups. Family Endogonacae includes the VAM. Between the cortical cells and a mycelium that spreads out in the soil, they generate branched haustorial structures known as arbuscules. Water and mineral salts are absorbed by this extraradical mycelium or hyphae. The main sites of solute exchange with the host are the arbuscules, which have a brief lifespan of 10–12 days. VAM fungus primarily falls under the genera Acaulospora, Gigaspora, Glomus, and Sclerocystis. Glomus is the most prevalent of these genera in soil. The VAM has been redesignated as AM because it was discovered that not all endomycorrhizal fungi develop vesicles as lipid-rich storage organs (arbuscular mycorrhiza). These fungi are drawn to the host plants’ root exudates, which contain flavonoids (such as -estradiol), and root infection and colonization take place. For fungi to flourish in mycorrhizal roots, a sizable fraction of the carbons fixed during photosynthesis is needed. The fungus is responsible for 87% of the greater root respiration in AM plants, which may be 20–30% higher than in non-mycorrhizal plants. Root and shoot growth is impacted by mycorrhizal colonisation differently. In contrast to nutrient-rich soils, its effects are more obvious in nutrient-poor soils. The plant can receive nutrients that are less mobile in soil, such as P, N, Zn, Cu, and S, thanks to mycorrhizal colonisation. Additionally, the mycorrhizal association enhances plant-water relationships (increases drought tolerance capacity), suppresses soil-borne bacterial and fungal root infections, and increases the hormonal (IAA, cytokinin, and ABA) content of plants (e.g. Pseudomonas syringae in tomato plant).

Organic Fertilisers

The waste from plants and animals that breaks down to produce nutrients necessary for plant growth is known as Organic fertilizers. These include compost (rotted farm wastes like sugarcane trash, paddy straw, etc.), sewage and sludge, vermicompost (earthworm-decomposed organic matter), Green manures (undecomposed plant material), and other livestock manures. Farmyard manures are composed of dung, urine, and litter from farm animals (poultry, sheep, and goat sweepings). Although they are administered in vast volumes, these organic manures only contain a small percentage of the nutrients. Organic farming is the process of cultivating crops without using chemical pesticides or herbicides and solely using organic fertilizers. In addition to providing nutrients, organic fertilizers enhance the physical characteristics of the soil, boost the availability of other nutrients, and manage worms and fungi that parasitize plants.

Benefits and Drawbacks of Biofertilizers

Biofertilizers are becoming increasingly important. This is due to the realization that using chemical fertilizers has detrimental impacts on both the environment and human health. They are also expensive and hard to come by. Consequently, the following are the benefits of employing biofertilizers in general:

1. They enrich the soil with nutrients and/or make them more available to the crops.

2. Some growth-promoting chemicals, such as indole acetic acid, are secreted by them (IAA).

3. They display antifungal properties under specific circumstances, shielding the plants from dangerous fungus.

4. They serve as inexpensive, environmentally beneficial alternatives to artificial fertilizers in agriculture.

5. They increase the soil’s water-holding capacity and porosity.

6. The germination of seeds is improved.

7. They improve soil fertility and fertilizer use efficiency, which ultimately results in a general production boost of 15-20%. However, the adoption of biofertilizers is constrained by the fact that the farming community does not embrace them very well because they do not yield immediate and dramatic results. Additionally, the amount of nutrients supplied by biofertilizers is insufficient to fully satisfy the crop’s need for high yields.

Frequently Asked Questions

Question: What is Biofertilizer for example?

Ans: Biofertilizers are organic fertilizers made of microbial inoculants of bacteria, fungi, and algae, either alone or in combination, which promote enhanced plant development through increased nutrient availability. Azorhizobium species

Question: What are Biofertilizers and types?

Ans: Biofertilizers are the following categories

1. Biological Nitrogen fixers, such as Rhizobium species for beans

2. Free-living, Non-Symbiotic Nitrogen fixers, such as Azotobacter and Azolla

3. Algae biofertilizers (using Azolla and blue-green algae (BGA))

4. Phosphate solubilizing bacteria (PSBs) 

5. Mycorrhiza

6. Organic Fertilizers

Question: Which plants are used as biofertilizers?

Ans: They enrich the soil with nutrients and/or make them more available to the crops.

Question: What are the benefits of biofertilizers?

Ans: They improve soil fertility and fertilizer use efficiency, which ultimately results in a general production boost of 15-20%. However, the adoption of biofertilizers is constrained by the fact that the farming community does not embrace them very well because they do not yield immediate and dramatic results. Additionally, the amount of nutrients supplied by biofertilizers is insufficient to fully satisfy the crop’s need for high yields.

Question: What is the purpose of biofertilizers?

Ans: They serve as inexpensive, environmentally beneficial alternatives to artificial fertilizers in agriculture. The germination of seeds is improved.

Question: Which bacteria is used as biofertilizer?

Ans: Rhizobium species

Question: Who discovered biofertilizers?

Ans: Dr. Goenadi

Question: Are biofertilizers organic?

Ans: Yes

Question: Is cow dung a biofertilizer?

Ans: Yes

Question: What pH is cow manure?

Ans: The pH of cow manure is between pH 8-12

Question: Which vegetables do not like manure?

Ans:  Potatoes

Question: Is compost a biofertilizer?

Ans: Yes