Introduction to Biofertilizers in agriculture: Biofertilizers are natural fertilizers that are microbial inoculants that live alone or in combination with bacteria, algae, and fungi and increase the availability of nutrients to plants. The role of biofertilizers in agriculture is of particular importance, especially in the current context of the rising cost of chemical fertilizers and their harmful effects on soil health. It is a substance that contains living microorganisms that colonize the rhizosphere or plant interior when applied to seeds, plant surfaces, or soil and increase the supply or availability of basic nutrients to the plant, and promotes development. Biofertilizers are not fertilizers.
A guide to types of Biofertilizers in agriculture, components, application, and benefits, disadvantages of Biofertilizers
What is Biofertilizer?
Biofertilizers consisting of living cells or latent cells of efficient strains of microorganisms that help plants growth obtain nutrients through their interaction in the rhizosphere when seeds or are planted through the soil. Biofertilizers directly increase soil fertility by adding nutrients. Biofertilizers add nutrients through the synthesis of environmental nitrogen fixes, phosphorus soluble, and plant growth-promoting substances.
Biofertilizers are products that contain the microorganisms necessary for soil fertility and plant growth when added to the soil. Biofertilizers are microbial inoculants that can generally be described as a preparation that contains living or dormant cells under the effective strain of nitrogen-fixing, phosphate solubilizing, and cellulite microorganisms. Biofertilizers are an economical, efficient, and renewable source of plant nutrients.
The biofertilizers in agricultural production are of particular importance, especially in the current context where the prices of agricultural commodities are skyrocketing. The selective strain of microorganisms should be used for biological fertilizer production, economic purpose, and significant results. When these bio-fertilizers are added to seeds, seedlings, plants, or soil, they improve crop yields and soil health through the process of biological nitrogen fixation. They also develop capsular polysaccharides to prevent soil erosion. They also convert immobilized chemicals into soluble forms and make them accessible to plants. Biofertilizers are more beneficial compared to chemical fertilizers.
Biological fertilizers contain microbes and living bacteria that promote soil fertility and plant growth. These microbes support the process of nitrogen fixation to produce the nutrients needed for plant growth.
The role of biofertilizers in agriculture
The role of biofertilizers is to make agriculture more sustainable and efficient. These products contain organic matter, thus adapting to the basis of avoiding synthetic and chemical additives to improve farming methods. Biofertilizers use microorganisms and materials that stimulate the natural processes in the soil. These processes affect the growth and development of plants. Therefore, biofertilizers improve plant growth. In contrast, fertilizer directly contributes to the growth of crops by providing additional nutrients to the soil or plants. Meanwhile, bio-fertilizers use soil microbes to improve plant nutrients. Different microorganisms have unique effects on plant growth. For example, Biofertilizers containing nitrogen-fixing bacteria affect growth by activating the nitrogen cycle. Usually, plants need nitrogen for ideal growth and development. Therefore, increasing the abundance of nitrogen-fixing bacteria in a plant’s rhizosphere will lead to better plant growth conditions.
Use of biofertilizers in agriculture – The use of biofertilizers in agriculture is moving away from the philosophy behind organic farming and using only naturally derived products. These are essential components of organic farming. Combined with organic, nutritious fertilizers, plants and soil provide a healthy growing environment that is sustainable for future growing seasons.
Biofertilizers are increasing plant resistance to pests and some abiotic pressures like drought, excess water, and extreme temperature level changes. Providing natural protection to plants against external hazards and limited conditions is essential for the successful growth and development of plants, and reduces the need for conventional, inorganic fertilizers and pesticides. Continued use of chemical inputs leads to soil pollution, runoff pollution, and ultimately degradation of healthy soil. Restricting traditional nutrients and pesticides, and changing organic modifications will help regenerate and maintain the overall health of their soils and improve plant growth and crop yields.
The demand for biofertilizers increases day by day. Despite this high demand, the availability of biofertilizers is limited due to increasing food production requirements, biofertilizer production challenges, and adequate storage, thus increasing the need for more biofertilizers. The good news is that biofertilizers have a long shelf life, are easy to use, are pollution-free, and are affordable.
The reason for using biofertilizers
At present, there is a growing concern about environmental hazards and the threats of sustainable agriculture. Because of the above facts, long-term use of organic fertilizers proves to be economical, environmentally friendly, more efficient, productive, and accessible to backward and small farmers as compared to chemical fertilizers. Thus the need to use biofertilizers arises mainly for two reasons. The first reason is the increase in the use of fertilizers leads to an increase in crop yields. Secondly, because the excessive use of chemical fertilizers damages the soil structure and creates other environmental problems.
More use of synthetic fertilizers has led to the pollution and contamination of the soil, which contaminates water basins, destroys microorganisms and friendly insects, increases crop risk of diseases, and reduces soil fertility.
Benefits of Biofertilizers
Some of the benefits associated with biofertilizers include;
- Biofertilizers are environmentally friendly and also cost-effective.
- Their use enriches the soil and improves the quality of the soil over time.
- Although they do not show immediate results, the results shown over time are spectacular.
- These fertilizers use environmental nitrogen and make them available directly to plants.
- They increase soil phosphorus content by releasing soluble and unavailable phosphorus.
- Biofertilizers improve root proliferation due to the growth of hormones.
- Microorganisms convert complex nutrients into simple nutrients for the availability of plants.
- Biological fertilizers contain microorganisms that promote the proper supply of nutrients and ensure proper growth.
- They help increase crop yield by 10-25%.
- Biofertilizers can protect plants to a certain extent from soil-borne diseases.
- Biofertilizers are living microorganisms of bacterial, fungal, and algae origin. Their method is different and can be applied individually or in combination.
- Biofertilizers fix the roots of environmental nitrogen and legume crops in the soil and make them available to plants. They dissolve insoluble forms of phosphate, such as tricalcium, iron, and aluminium phosphate, in available forms.
- They scavenge phosphate from the soil layers. They produce hormones and anti-metabolites that promote root growth. They dissolve organic matter and help produce minerals in the soil.
- Biofertilizers increase the availability of nutrients and increase yields by 10 to 25%.
- Increase crop yields – Biofertilizers primarily promote plant growth and improve crop yields like traditional chemical fertilizers. However, biofertilizers improve soil health by achieving higher crop yields. The use of biofertilizers can be especially helpful in maintaining the natural fertility of the soil as these products keep the soil chemical-free.
- Easily accessible – Biofertilizers are cost-effective. Low-income farmers can use this organic product while maintaining ideal crop yields. Also, these materials are easy to apply because they are still types of input products such as chemical fertilizers that farmers may be accustomed to using. Note, however, that biofertilizers are not fertilizers in the strict sense of the word.
- Increases plant resistance to abiotic stress – Biofertilizers contain materials that promote plant resistance to growing conditions such as drought, severe cold, water excess or deficits, and saline soils. Biofertilizers improve a plant’s abiotic stress resistance, and they are more likely to maintain ideal growth rates. As plants thrive in limited states, farmers can maintain crop yields and meet the growing demand for agricultural products.
Types of Biofertilizers
Their association with many microorganisms and crop plants is being exploited in the production of biofertilizers. Though, they can be grouped in different ways depending on their nature and function.
The types of biofertilizers include;
Bio compost is one of the eco-friendly products containing waste products from the sugar industry that have decomposed. It is made up of human-friendly bacteria, fungi, and various plants.
It is an eco-friendly and non-pathogenic product used in various crops as well as in horticultural and ornamental plants, such as Paddy, Apple, Sugarcane, Eggplant, Corn, Cotton, Vegetables, and Lemons, etc. It acts as a productive destroyer and antagonistic hyper parasitic against many bored eggs, hyper-parasites, shoots, fruits, leaves, flower-eaters, and other pathogens in the field.
Rhizobium is a soil habitat bacterium that colonizes legume roots and symbolically fixes atmospheric nitrogen. The morphology and physiology of the rhizobium vary from free to nodules to bacteroids. They are the most effective biofertilizer in terms of relative nitrogen content. They have seven genera and are highly specialized in nodule formation in legumes, called cross-inoculation groups.
This is the most important nitrogen-fixing organism. The root of the symbolic plant is leguminous in the nodule and provides nitrogen to the plant through nitrogen fixation. Beneficial crops are Peanuts, Soybeans, Red Gram, Green Gram, Black Gram, Lentils, Bean Peas, Bengal Gram, and Fodder Pulses.
Of the many species of Azotobacter, A. chroococcum can be fixing N2 (2-15 mg N2 fixed / g carbon source) in arable land. Bacteria produce abundant slime which helps in soil aggregation. The number of A. chroococcum in Indian soils exceeds about 105/g soil due to lack of organic matter. Azotobacter biofertilizer is suggested for non-leguminous crops like Paddy, Wheat, Millet, Cotton, Tomato, Cabbage, Mustard, Saffron, and Sunflower. It works well if the soil organic matter content is high.
This is an important and well-known free-living nitrogen that fixing aerobic bacteria. It is used as a biofertilizer for all non-leguminous crops like Rice, Cotton, and Vegetables, etc. Azotobacter cells are not present in the rhizosphere but are abundant in the rhizosphere region.
Most beneficiary crops are Wheat, Millet, Barley, Corn, Paddy, Mustard, Sunflower, Sesame, Cotton, Sugarcane, Banana, Grape, Papaya, Watermelon, Onion, Potato, Tomato, Cabbage, Pepper, Lady Finger, Rapeseed, Linseed, and Tobacco. Mulberry, Coconut, Spices, Fruits, Flowers. Other types of planting crops, forest plants.
A. brasilense and Azospirillum lipoferum are the basic inhabitants of the soil, the rhizosphere, and intercellular spaces of the root cortex of graminaceous plants. They form an associative symbiotic relationship with graminaceous plants. In addition to nitrogen fixation, there are some additional benefits of inoculation with Azospirillum to produce growth-promoting substances (IAA), disease resistance, and drought tolerance.
It belongs to bacteria and fix large amounts of nitrogen in the range of about 20-40 kg N/ha in non-leguminous plants. Some non-leguminous plants are Cereals, Millets, Oilseeds, and Cotton, etc.
Azolla is a free-floating water fern that floats in water and combines with nitrogen to fix atmospheric nitrogen. It is an alternative nitrogen source or a supplement to commercial nitrogen fertilizers. Azolla is used as a biofertilizer for wetland rice and contributes 40-60 kg per hectare to the rice crop.
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Azolla contains cyanobacteria that are used as biofertilizers. Cyanobacteria produce a range of toxic substances that are dangerous to humans and animals called cyanotoxins. It contains up to 60 kg of nitrogen and enriches the soil with organic matter.
Plant growth-promoting rhizobacteria (PGPR)
The groups of bacteria that colonize roots or rhizosphere soils and are beneficial to crops are called plant growth-promoting rhizobacteria (PGPR). PGPR inoculants promote growth through plant disease (called bioprotectants), improved nutrition (biofertilizers), or phytohormone production (biostimulants).
The species Pseudomonas and Bacillus have not yet been able to produce good quality phytohormones or growth regulators due to the high amount of fine roots in the crops which has the effect of absorbing plant roots to obtain water and nutrients. The level has to be raised. These PGPRs are called biostimulants and the phytohormones they produce include indole acetic acid, cytokines, gibberellins, and inhibitors of ethylene.
Potassium Mobilizing Biofertilizer (KMB)
The availability of potassium (K) in the soil is also affected by microbial activity in the rhizosphere that removes K from the non-convertible reserve. These microorganisms are commonly known as potassium solubilizing bacteria or potassium-soluble bacteria.
Zinc Solubilizing Biofertilizer (ZSB)
Some microbes can dissolve zinc in a soluble form by the secretion of certain organic acids, and this zinc soluble bacterium is known to be primarily from the genus Bacillus. Beneficial crops are Cereals, Millet, Pulses, Vegetables, Fiber, and Oilseed Crops.
Phosphate Absorbers Mycorrhizaeaeaeae
It is a symbiotic association between the host plant and a certain group of fungi in the root system, in which the fungal partner derives its carbon needs from the host’s photosynthesis and the host receive a particularly high amount of nutrients and it is beneficial. Calcium, phosphorus, copper, zinc, etc., are inaccessible to the fungus with the help of finely absorbed hyphae. These fungi are associated with the majority of crops. They are found everywhere in the geographical distribution that grows evenly with plants in the Artic, temperate and tropical regions. VAMs are found in a wide range of ecosystems, from aquatic to the desert.
Recommended biofertilizer for crops
- For pulse crops, Rhizobium + Phosphotika at 200 gm per 10 kg seed is recommended. Some of the important pulse crops are pigeon pea, green gram, black gram, and cowpea, etc., groundnut, and soybean.
- For every 10 kg, seed treatment, Azotobacter + Phosphotika at 200 gm are useful for Wheat, Millet, Maize, Cotton, and Mustard, etc.
- For transplanted rice, it is recommended to dip the seedling roots in an Azospirillum + Phosphotika solution at 5 kg/ha for 8 to 10 hours.
Components of biofertilizers
The main components of biofertilizers are as follows.
Symbiotic nitrogen-fixing bacteria
Rhizobium is one of the major nitrogen-fixing bacteria. Here the bacteria take shelter and get food from the plants. In turn, they help plants by providing fixed nitrogen.
Symbiotic nitrogen-fixing Cyanobacteria
It is blue-green algae or cyanobacteria with symbiotic association with many plants. Some of the nitrogen-fixing cyanobacteria are liverworts, cycad roots, ferns, and lichens. Anabaena fern leaves are found in the grasses. It is responsible for determining nitrogen. Azolla pinnate is a fern that resides in rice fields but does not regulate plant growth.
Free-living nitrogen-fixing bacteria
They are free-living soil bacteria that fix nitrogen. They are saprotrophic anaerobes like Clostridium beijerinckii, and Azotobacter, etc.
Rhizobium and Azospirillum are the most widely used of all the types of biofertilizers.
Other Components of biofertilizers are;
This group symbolically fixes nitrogen. Nitrogen biofertilizers help to fix nitrogen levels in the soil. Nitrogen is a limiting factor for plant growth because plants need a certain amount of nitrogen in the soil for growth. Different biofertilizers have different effects for different soils, so the use of nitrogen bio-fertilizers depends on the crop grown.
The cultivated crop determines what type of nitrogen fertilizer to use;
- Rhizobium for legume crops.
- Azotobacter / Azospirillum biofertilizers for non-legume crops.
- Acetobacter for sugarcane only.
- Blue-green algae (BGA) and Azolla rice were used for low-paddy land.
Phosphorus is a limiting factor for plant growth. Phosphorus biofertilizers help the soil to reach the maximum level of phosphorus and to correct the level of phosphorus in the soil. Unlike nitrogen biofertilizers, the use of phosphorus biofertilizers does not depend on the crops grown on the land. Phosphatika is also called phosphate solubilizing bacteria; it is used for all crops with Rhizobium, Azotobacter, Azospirillum, and Acetobacter.
Phosphate soluble biofertilizers
Phosphate solubilizing biofertilizers use phosphate solubilizing microorganisms (PSMs) to help promote plant growth. Though, these beneficial microbes can hydrolyze organic and inorganic soluble phosphorus compounds into soluble forms. In other words, PSM converts phosphorus compounds into water-soluble formats to help absorb the plant element. These biofertilizers include bacteria like Bacillus megaterium, Bacillus circulans, and Pseudomonas striata. Essential fungi such as Penicillium and Aspergillus species also contributed to phosphate soluble fertilizers.
Phosphorus fixing biofertilizers
Phosphorus biofertilizers are not dependent on land crops.
Phosphatica should be used for all crops to be applied with
- Azospirillum and Acetobacter.
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Biofertilizers are used to enrich compost and increase the bacterial process that breaks down compost waste. Biofertilizers suitable for fertilizer use are cellulolytic fungal cultures and phosphotica and Azotobacter cultures. 100% pure eco-friendly organic fertilizer is vermicomposting – this organic fertilizer contains Nitrogen, Phosphorus, Potassium, Organic Carbon, Sulfur, Hormones, Vitamins, Enzymes, and Antibiotics, which help to improve product quality and quantity. It has been observed that due to continuous misuse of chemical fertilizers, the soil loses its fertility and becomes salty day by day. Natural farming is the only treatment to overcome such problems and Vermicomposting is the best solution.
Another eco-friendly organic fertilizer made from waste materials from the sugar industry that is enriched by decomposing various plants and human-friendly bacteria and fungi is bio-compost. Bio compost contains nitrogen, phosphate soluble bacteria, and various beneficial fungi such as the decaying fungus Trichoderma viridae, which protects plants from various soil-borne diseases and also helps to increase soil fertility. The result is good quality produce for farmers.
Methods of application of Biofertilizers
Seed treatment – In seed treatment, about 200 grams of biofertilizer is suspended in 300 to 400 ml of water and mixed with 10 kg of seeds and adhesive like gum acacia, and jiggery solution, etc., is used. The seeds are then spread on a clean sheet or cloth under shade to dry and used immediately for sowing.
Seedling Root Dip – This is mainly used for transplanted crops. A bed is made in the field for the rice crop and filled with water. The recommended biofertilizers are added to this water and the plant roots are dipped for 8 to 10 hours and transplanted.
Soil treatment – About 4 kg biofertilizers are each recommended mixed with 200 kg of compost and kept overnight. Then, this mixture is added to the soil at the time of sowing or planting.
How could get a good response to biofertilizer applications in agriculture?
Tips for responding well to biofertilizer applications are;
- Biofertilizer has a good effective strain and is free from contaminated microorganisms.
- Choose the right combination of organic fertilizers and apply before the expiry date.
- Use the suggested application method and apply at the appropriate time according to the information on the label.
- For better results, use a suitable adhesive for seed treatment.
- Use corrective methods for troubled soils such as piercing lime or gypsum seeds or using lime to improve soil pH.
- Ensure the supply of phosphorus and other types of nutrients.
Precautions to take while using biofertilizers
- Biofertilizer packets are stored in a cool and dry place.
- The right combination of bio-fertilizers must be used. Because rhizobium is crop-specific, one should only use it for a specific crop. Other chemicals are not mixed with biofertilizers.
- When purchasing, make sure that each packet provides the necessary information such as product name, crop name for which it is intended, manufacturer’s name and address, date of manufacture, expiration date, batch number, and instructions for use.
- The packet must be used before it expires, only for the specific crop and in the manner suggested by the application.
- Biofertilizers need care in storage. Both nitrogen and phosphatic biofertilizers should be used for the best results. It is important to use bio-fertilizers with chemical fertilizers and organic fertilizers. Biofertilizers are not a substitute for fertilizers but can meet the nutritional requirements of plants.
Disadvantages of biofertilizers
- Biofertilizers are a supplement to chemical fertilizers but not a substitute.
- Biofertilizers result in a 20-30% increase in crop yields. They do not significantly increase the productivity of chemical fertilizers.
- Certain crops require specific fertilizers. This applies more to symbiotic microorganisms. If non-specific rhizobium is used as fertilizer, it will not cause root nodulation and increase crop yield.
- If exposed to sunlight for long periods, microbes are killed because they are sensitive to light.
- Microbial fertilizer should be used within six months after storage at room temperature and two years if stored at cooling temperature.
- The effectiveness of microbial fertilizers depends on the role of the soil, such as moisture content, pH, temperature, organic matter, and types of micro-organisms present. When these factors are invasive, microbial fertilizers may not be effective in increasing soil fertility.
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