Agricultural workers are increasingly turning to organic farming practices to balance crop input and output economics, while becoming increasingly conscious of environmental changes due to climate change. The impacts of a changing climate are already noticeable in the soils, seen by reduced moisture content brought on by increased drought and heat, in addition to years of applying synthetic fertilizers and stripping the soils of its natural microbiome. These compounding effects have led to reduced plant growth and development.
Organic agriculture excludes chemical and synthetic compounds to improve farming practices. Growers transitioning to organic farming utilize organic substances, such as compost and cow dung manure. Farmers add these to their lands to avoid using chemical substances, operating under the philosophy of going back to nature.
Similarly, natural farming is a chemical free farming method encouraging growers to adopt non-chemical practices. One key difference between organic farming and natural farming is additives. While organic farming encourages farmers to substitute chemical fertilizers for organic fertilizers, natural farming discourages adding external fertilizers altogether. (SOURCE).
Synthetic fertilizers are composed of chemically derived nutrients, often containing fewer nutrients but higher concentrations of nitrogen, phosphorus, and potassium. Made in plant available forms, synthetics make it easy to apply what is needed to the plant. However, because the nutrients are in an inorganic form they are quickly leached out of the soils leading to runoff into waterways and disrupting surrounding ecosystems. Organic fertilizers are derived from plants and animals and provide nutrients available to plants and soil microorganisms. Because of this, can improve water movement and soil structure. Organic fertilizers provide all essential macro and micro nutrients to the plants and soils, without disrupting the natural nutrient cycling. Biofertilizers are defined as containing living microorganisms and naturally derived substances. Biofertilizers offer essential nutrients without polluting the soil with synthetic materials, but rather leads to the regeneration of soil and plant health. Below, we discuss biofertilizers, the different types, and their role in the future of sustainable agriculture.
The Use of Biofertilizers in Agriculture
The philosophy behind organic farming is moving away from synthetics and only applying naturally derived products.. Biofertilizers are essential components of organic farming practices because combining naturally occurring microorganisms with organically derived, nutrient-rich fertilizers, provides the plants and soils with a healthy growing environment that is sustainable for future growing seasons. Biofertilizers also enhance a plant’s resistance against pests and abiotic stressors such as drought, excess water, and extreme temperature changes. Providing plants with natural protection against external threats and restrictive conditions is necessary for successful plant growth and development, and reduces the need for traditional, inorganic fertilizers and pesticides.
Constant application of chemical inputs causes soil contamination, downstream pollution, and eventual degradation of healthy soils. By limiting traditional nutrient inputs and pesticides, and switching to organic amendments will help regenerate and maintain their overall soil health and improve plant growth and crop yields.
As more farmers adopt organic farming methods, the demand for biofertilizer rises. The global biofertilizer market size in 2019 was worth US$1 billion. Despite this high demand, biofertilizer availability remains limited due to the increasing needs of food production, biofertilizer production challenges, and proper storage, thus prompting the need for more biofertilizers. The good news is that biofertilizers have long shelf lives, are easy to use, are free of contamination, and are inexpensive.
What Are Biofertilizers?
Simply put, biofertilizers are products containing microorganisms that promote plant growth. Strictly speaking, these products are not fertilizers, despite their name and classification.
Although both fertilizers and biofertilizers are input products meant to improve plant growth and development, the difference lies in how they affect such growth and development. Fertilizers directly enhance plant growth and development by supplying extra nutrients to the soil or the plant.
Meanwhile, biofertilizers indirectly enhance plant growth and development by utilizing microorganisms to enhance natural processes in the soil that affect plant growth. Different types of bacteria stimulate various biological activities in the ground. In addition, some microbes may work better than others depending on the environment, and learning about the different types of biofertilizers will help growers choose the best product for their crops.
What Are the Types of Biofertilizers?
Several biofertilizers have species that perform a series of functions from nutrient turnover, abiotic stress tolerance, carbon sequestration, all leading to increased plant quality and yield. The application method for the different biofertilizer types varies depending on crop type and growing environment. In general, there are seven different types of biofertilizers based on their function and nature:
“Reducing the need for organic fertilizers”
Group 1: Nitrogen-Fixing Biofertilizers
Nitrogen-fixing biofertilizers contain microorganisms that are essential players in the natural nitrogen cycle. These microorganisms help convert atmospheric nitrogen into ammonia through nitrogen fixation, which plants can utilize. Thus, nitrogen fixation is the process of binding nitrogen into usable forms for the benefit of other living organisms.
There are three primary nitrogen-fixing bacteria in biofertilizers:
- Free-Living Nitrogen-Fixing Bacteria: These bacteria are saprotrophic anaerobes or microorganisms that gain nourishment by feeding on nonliving, decaying, or rotten organic matter. Azotobacter, Clostridium, Anabaena, and Nostoc are common saprotrophs that biofertilizer manufacturers utilize for their nitrogen-fixing biofertilizer products. Biofertilizers based on free-living nitrogen-fixing bacteria are ideal products for non-leguminous plants, mainly cotton, rice, and vegetables.
The Azotobacter genus is the primary free-living nitrogen-fixing bacteria found in biofertilizers. It is an aerobic bacteria, so nitrogen fixation occurs by reducing the oxygen concentration intracellularly. These bacteria use the energy from oxidized organic molecules.
In addition, Azotobacter bacteria are absent on the rhizoplane or the immediate surface of a plant’s root. However, these cells are abundant in the rhizosphere, or the soil volume surrounding the rhizoplane, where root activities occur to help promote plant growth.
The lack of organic matter in the soil limits Azotobacter proliferation, making Azotobacter-based nitrogen-fixing biofertilizers ideal products to boost the establishment of this bacteria in the rhizosphere. Increasing the abundance of free-living nitrogen-fixing bacteria increases nitrogen cycling, leading to overall increased plant growth and crop yield.
Free-living nitrogen-fixing bacteria may not contribute as much fixed (or reactive) nitrogen as other types of nitrogen-fixing bacteria. A study mentioned how this type of bacteria can only fix one-tenth of the total atmospheric nitrogen that symbiotic nitrogen-fixing bacteria can. This limited ability to bind nitrogen into useful forms may pose problems for plants that utilize fixed nitrogen.
- Associative Symbiotic Nitrogen-Fixing Bacteria: Some sources refer to this type of nitrogen-fixing bacteria as a loose association of nitrogen-fixing bacteria. Species of the Azospirillum, Herbaspirillum, Klebsiella, Enterobacter, and Paenibacillus genera are associative nitrogen fixers. Associative nitrogen-fixation occurs when the bacteria converts nitrogen gas into ammonia without having an symbiotic relationship with host plants, which explains why some refer to these bacteria as loose association.
Experts have mostly reported the presence of associative nitrogen-fixing bacteria on corn, sugarcane, and wheat plant roots. These also bacteria produce organic compounds which the bacteria use as carbon sources for nitrogen fixation.
A 2016 study places this type of nitrogen-fixing bacteria between free-living and symbiotic nitrogen-fixing bacteria regarding the amount of nitrogen they can fix. One source states that these bacteria can fix a considerable quantity of nitrogen within the 20 kg/ha and 40 kg/ha range in the rhizosphere of cereals, cotton, millets, and oilseeds.
- Symbiotic Nitrogen-Fixing Bacteria: This type of bacteria occupies a host plant’s root hairs. Symbiotic nitrogen-fixing bacteria multiply in a host plant’s root area to help encourage root nodule formation and plant cell enlargement. This action leads to significant plant growth and may affect the overall crop yield. Common examples of symbiotic nitrogen-fixing bacteria include Rhizobium spp, Frankia spp, and Anabaena azollae.
Rhizobium species are a classic example of symbiotic nitrogen-fixing bacteria. As they invade the plant’s root nodule for shelter and nutrients from the host plant, they reduce molecular nitrogen into ammonia. Plants utilize ammonia as a building block to produce necessary nitrogen-containing compounds, including proteins and vitamins.
This symbiotic relationship between the host plants and bacteria proves to be effective for different crops. A source highlights several Rhizobium species from other host groups and their nitrogen-fixation rate for various crops, including green pea, lentil, soybean, lupine, sweet clover, wild bean, clover, mung bean, pigeon pea, cowpea, groundnut, and chickpea.
The study stated that the quantity of biological nitrogen that these Rhizobium bacteria species fixed in different crops was between 57 kg/ha and 150 kg/ha. Note that the various species were specific to their host groups and fixed exact amounts of nitrogen in kilograms per hectare.
Group 2: Phosphate Solubilizing Biofertilizers
Phosphate solubilizing biofertilizers utilize phosphate solubilizing microorganisms (PSMs) to help promote plant growth. These beneficial microbes can hydrolyze organic and inorganic insoluble phosphorus compounds into soluble forms. In other words, PSMs convert phosphorus compounds into water-soluble formats to help a plant’s uptake of the element. Phosphorus is an essential nutrient for plant growth and development.
Phosphate solubilizing biofertilizers may include bacteria such as Bacillus megaterium, Bacillus circulans, and Pseudomonas striata. Essential fungi such as Penicillium and Aspergillus species also contribute to phosphate solubilizing fertilizers.
A study highlighting the biotechnological aspects of mangrove microorganisms mentions phosphate solubilizing bacteria. The study stated that these microbes are potential protective suppliers of soluble phosphorus for mangrove plants. The study also noted that such bacteria are abundant in Mexico’s mangrove ecosystems, where experts constantly explore and discover new bacteria.
Meanwhile, a separate study explores the potential of phosphate solubilizing bacteria as crucial players in the agricultural sector for their natural ability to make soluble phosphorus available to crops. This study explains that phosphate solubilizing bacteria convert phosphorus into soluble forms to lower soil pH and make phosphorus more available to plants.
Group 3: Phosphate Mobilizing Biofertilizers
Phosphate mobilizing biofertilizers contain mycorrhizal fungi, acting as phosphate absorbers. These microorganisms are similar to symbiotic nitrogen-fixing bacteria because they establish a symbiotic relationship with plants through their root systems.
Ectomycorrhizal (ECM) fungi and arbuscular mycorrhizal fungi (AMF) are the two major types of mycorrhizae for biofertilizers, with AMF being the most common. AMF occurs in grasses, shrubs, and certain tree species. Mycorrhizal fungi are symbiotic with over 90% of all vascular plant species, including maize, wheat, rice, and potato. The fungi benefit from these plants and other compatible crops by penetrating the root cells of the host plants to obtain nutrients that these fungi offer in return, such as phosphorus, calcium, copper, and zinc. Applying this relationship to large scale crop production, biofertilizers increase plant health and allow for a more sustainable crop.
A review from 2017 mentioned the increasing interest among experts in utilizing mycorrhiza to promote sustainable agriculture. Experts associate mycorrhiza’s symbiosis with benefits to water balance, abiotic stress protection, and plant nutrition efficiency, including micronutrients and macronutrients, especially phosphorus.
The study also cited biofertilizers based on Glomus species (specifically Glomus mosseae or Glomus fasciculatum) from chopped, dried corn roots as ideal products that serve as biocontrol agents of soil-borne diseases. The study mentioned banana, corn, eggplant, fruit crops, onion, papaya, peanut, sugarcane, tomato, watermelon, and pepper as possible plants that may benefit from such biofertilizers.
Group 4: Potassium Solubilizing Biofertilizers
Potassium is another essential nutrient for plant growth. Experts associate microorganisms such as Bacillus edaphicus, Paenibacillus glucanolyticus, and Bacillus mucilaginosus as important species in breaking down insoluble potassium. Experts noted how B. edaphicus increased potassium uptake in wheat plants, while P. glucanolyticus can increase the dry weight of black pepper.
- mucilaginosus also has plant growth promotion potential when experts combine the bacteria’s effects with phosphate solubilizing bacteria to promote cucumber, eggplant, and pepper plant growth. At the same time, this potassium solubilizing bacteria offered higher biomass yields in Sudan grass.
Group 5: Biofertilizers for Micronutrients
Biofertilizers that utilize micronutrients promote plant growth and development by providing the essential plant nutrients that are found in trace amounts in plant tissues. These trace plant nutrients are key players in plant nutrition and productivity. Some essential micronutrients imperative to plant growth and development include boron, chlorine, copper, iron, manganese, molybdenum, zinc, and nickel. (SOURCE)
This type of biofertilizer includes microorganisms capable of degrading silicates and zinc. Silicate-soluble bacteria (SSB) are microbes that weather silicon from silicates to promote plant growth and development. In other words, SSB break down silicate into plant usable nutrients. There are also microbes that solubilize micronutrients like zinc, iron, and copper, and then convert them into a plant-available form.
Micronutrient biofertilizers are potentially cheaper alternatives to traditional fertilizers such as zinc sulfate, which can be expensive. These species extract zinc that occurs naturally in soluble forms, like zinc oxide, zinc carbonate, and zinc sulfide, making a cost-effective investment over traditional fertilizers with synthetic zinc additives. (SOURCE)
Group 6: Plant Growth-Promoting Rhizobacteria
Plant growth-promoting rhizobacteria (PGPR) are biofertilizers that utilize rhizobacteria or microbes that naturally occur in the rhizosphere for their beneficial effects on plant growth. As mentioned in a previous section, the rhizosphere is the soil volume surrounding the rhizoplane where root activities occur to help promote plant growth. PGPR products stimulate plant growth and development by encouraging the rhizobacteria to conduct their natural processes associated with plant growth.
All the microorganisms mentioned herein that poses some ability to solubilize nutrients for plant uptake and growth promotion can be classified as PGPRs, but Rhizobacteria may include several genera such as:
- Pseudomonas species
Although these bacteria have various mechanisms in promoting plant growth and development, they generally influence plant growth by solubilizing phosphate to enhance nutrient uptake among plant growth.
One review cited a study that showed how bacteria within the genus Achromobacter expressed positive effects in improving root hair number and length in oilseed rape plants. The study further explored the rhizobacteria’s impact on the plant’s dry weight of the root and shoot. Applying the biofertilizer led to a shoot dry weight increase between 22% and 33% and a root dry weight increase between 6% and 21%.
This ability of rhizobacteria makes some people refer to PGPRs as biostimulants. However, biostimulants are separate product classes that mostly remain to be unclassified as of yet. All PGPR products contain rhizobacteria to enhance plant growth, development, and resistance. However, biostimulants may or may not contain living organisms. The difficulty with separating PGPRs and biostimulants as different product classes is their application method.
Biofertilizers apply to the soil or directly to the plant. Meanwhile, the European Biostimulants Industry Council (EBIC) defines biostimulants as products that contain substances or microorganisms that encourage natural processes through the rhizosphere. As such, products affecting plant growth through the rhizosphere may classify as biostimulants.
Note that experts only generally accept this definition. Some biostimulants can encourage plant growth without application in the rhizosphere, for example through foliar applications. This inconsistency makes it difficult to classify biostimulants as separate products from biofertilizers officially.
Group 7: Compost Biofertilizers
Compost is a mixture of decomposing plant and food waste, that breaks down into an organic, nutrient rich fertilizer. Many farmers use composting as an affordable, sustainable way to fertilize to enhance crop and soil health. The breakdown of organic matter is dependent on several factors like temperature, moisture, and oxygen, and can be enhanced by the addition of organisms like worms or microorganisms like fungi and bacteria. General classifications of composts as described in a European Commission-supported publication include:
- Rural Compost: Composting in farms. Raw materials for rural composts include fruit and vegetable waste, biogas plant slurry, straw, hay, leaves, and cattle-shed bedding. These products may contain 0.5 % nitrogen, 0.2% phosphorus pentoxide, and 0.5% potassium oxide. Farmers usually use rural compost as bulky organic manure.
- Urban Compost: Composting in the city. Raw materials for urban composts include city garbage, sewage sludge, industrial waste, and factory waste. These composts usually contain 1.5%-2.0% nitrogen, 1.0% phosphorus pentoxide, and 1.5% potassium oxide. Some commercial urban compost may contain small amounts of other micronutrients such as 1% iron, 375mg/kg copper, 705mg/kg zinc, and 740mg/kg manganese.
- Vermicompost: Composting using beneficial microorganisms, earthworm cocoons, excreta, plant nutrients, actinomycetes (gram-positive bacteria), enzymes, hormones, and organic matter. These compost fertilizers may contain 0.6% nitrogen, 1.5% phosphorus pentoxide, and 0.4% potassium oxide. These composts may also contain an average of 22 mg/kg iron, 13 mg/kg zinc, 19 mg/kg manganese, and 6 mg/kg copper.
Biofertilizer Pros and Cons
As biofertilizers become more widely used, growers are considering the advantages and disadvantages of applying biofertilizers. The primary advantage of biofertilizers is their ability to provide an environmentally friendly alternative to chemical fertilizers. Biofertilizers offer the essential nutrients for plant growth and development without harming the soils.
At the same time, this substitution may count as a disadvantage of biofertilizers, but this is because they cannot be treated like traditional chemical fertilizers. The same amount of biofertilizers and chemical fertilizers do not offer the same nutritional value. Chemical fertilizers, as synthetic materials, tend to provide more nutrients for plant and crop growth. As such, farmers may need more biofertilizer products to achieve the same effect.
Here’s a closer look at the pros and cons of biofertilizers as products and their benefits on plant growth and development.
Advantages of Biofertilizers
- Increase Crop Yields: Biofertilizers essentially boost plant growth and improve crop yields like traditional chemical fertilizers. However, since biofertilizers use organic material, they enhance soil health while achieving higher crop yields. Suffice to say, using biofertilizers exclusively may help maintain natural soil fertility as these products keep the soil chemical-free.
- User-Friendly and Easily Accessible Materials: Biofertilizers are cost-effective options for farmers looking for affordable alternatives to sustain their land and crop production. Low-income farmers can utilize this organic product while maintaining an ideal crop yield. In addition, these materials are easy to apply since they are still types of input products like chemical fertilizers that farmers may be used to using. However, note that biofertilizers are not fertilizers in a strict sense of the word.
- Enhances a Plant’s Resistance Against Abiotic Stress: Biofertilizers contain materials that promote a plant’s resistance against restrictive growing conditions such as drought, extreme cold, water excess or deficit, and high-salinity soil. As biofertilizers improve a plant’s abiotic stress defenses, they are more likely to maintain an ideal growth rate despite harsh climates or unfavorable weather conditions. As plants thrive in restrictive states, farmers can maintain crop production and supply the growing demand for agricultural products.
- Suitable Replacement for Chemical Fertilizers: Biofertilizers utilize beneficial substances for long-term plant and soil health. Without proper handling and sufficient knowledge of such products, chemical fertilizer poses toxic risks to overall plant health, the environment, and consumers after harvesting the chemically fertilized plant.
- Great Substitute for Other Input Materials: Biofertilizers are natural alternatives for plant growth promotion, pathogen combat, and pest prevention. In essence, biofertilizers can minimize the need for traditional fertilizers and pesticide inputs, which are not beneficial for long-term plant health as these materials contain synthetic compounds.
- Sustainable Biofertilizer Production: Biofertilizers can be by-products of generating electricity with biogas. Biogas generators utilize renewable energy from organic matter such as animal waste or particular crops. Once these machines entirely use up the biofuel to produce biogas, the remaining matter may serve as biofertilizers, essentially creating a sustainable practice.
Disadvantages of Biofertilizers
- Require More Product: Although biofertilizers and chemical fertilizers have the same goal of improving plant growth and increasing plant yield, some biofertilizers tend to contain a lower nutrient density than chemical fertilizers. In other words, farmers may need a larger amount of biofertilizers to achieve the same effect that a small amount of chemical fertilizer may provide. However, since biofertilizers are cost-effective and sustainable, this disadvantage is easily manageable. Impello biofertilizers are concentrated to overcome this disadvantage therefore one will need significantly less product than traditional fertilizer.
- Require Immediate Application: Since biofertilizers are organic materials, some of these products may have a much shorter shelf-life than chemical fertilizers. As such, users may have a difficult time storing these products for later use. The special formulations of Impello, however, have overcome this challenge and are extremely stable with a longer than normal shelf life.
- Exclusive Biofertilizer Production: Although producing biofertilizers can be sustainable as a biogas by-product, production still requires specific machinery. These machines for creating biofertilizers may be challenging to come by, especially for smaller-scale, lower-income farmers seeking alternative sustainable organic farming methods.
- Have Different Types for Different Uses: Some biofertilizers may work only for specific plants. The effects of one type of biofertilizer on one plant may not manifest in another species, making knowledge on the different types of biofertilizers essential when choosing a product for a specific crop. At the same time, this disadvantage may be an advantage for some because the variety of biofertilizers may open possibilities of expanding the kinds of crops a farmer grows.
- Have Distinct Odors: This minor disadvantage may only be relevant to some odor-sensitive users. Biofertilizers tend to have pungent odors that may be difficult to work with if someone is sensitive to strong scents, but this is because these products are made of organic substances and often contain living organisms..
Conclusion: The Role of Biofertilizers in Organic Farming
The role of biofertilizers is to create a more sustainable and efficient way of doing agriculture. These products contain organic matter, thus aligning with the premise of avoiding synthetic and chemical additives for improving farming practices.
Biofertilizers utilize microorganisms and materials that stimulate the natural processes in the soil. These processes affect plant growth and development. So, biofertilizers indirectly improve plant growth by enhancing the biological processes through microorganisms. In contrast, fertilizers directly help crops grow by supplying extra nutrients to the soil or plant. Meanwhile, biofertilizers utilize the existing microbes in the earth to help improve a plant’s nutrient uptake.
Different microorganisms offer unique effects on plant uptake. For instance, biofertilizers containing nitrogen-fixing bacteria impact growth by stimulating the nitrogen cycle. Plants need nitrogen for ideal growth and development. So, by increasing the abundance of nitrogen-fixing bacteria in a plant’s rhizosphere, the plant would have better-growing conditions.
Despite the clear advantage of biofertilizers in organic farming, these products have some strikes against them. Among these disadvantages is biofertilizer availability. The demand for biofertilizers is high and growing, yet the product’s availability cannot keep up.
The call for more advanced biofertilizers is imperative to changing agriculture in a way that is sustainable for a changing climate, growing global population, and increasing farming efficiency and sustainability. Biofertilizers thus are excellent tools for promoting organic farming. These products enhance plant growth through natural processes and organic materials, eliminating the dependence on potentially harmful synthetic and chemical substances.
Impello’s integrated solutions, ranging from microorganisms to other bioactive compounds, help farmers everywhere increase the quality and yield of every harvest. Consider this product line when intending to adopt biofertilizers as an initial venture into organic farming.
- slide: https://www.slideshare.net/nandhinirajan549/biofertilizers-organic-farming
- production: https://pubs.acs.org/doi/10.1021/acs.est.8b01619
- n-fixing: https://openprairie.sdstate.edu/cgi/viewcontent.cgi?article=1688&context=etd
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