Due to the increasing demand of agricultural products which results from rapid increase in urbanization, it has become essential for a method to increase agricultural productivity by using various means to boost agricultural yields. The use of fertilizers have been found to be very helpful in achieving the targets of food production, but with the tremendous use of the chemical (inorganic) fertilizer, the soil physicochemical parameters have been seriously affected, as this approach causes depletion in the essential minerals of the soil which in turn reduces soil fertility. So to overcome this challenge, it has become imperative to adopt a different approach which will serve as a replacement and remedy. Hence the adoption of biofertilizers also known as organic fertilizer becomes an eco-friendly approach. The application of biofertilizers (microbial inoculants) is a promising technology for future sustainable farming systems in view of rapidly decreasing phosphate stocks and the need to more efficiently use of available nitrogen. Various microbial taxa are currently used as biofertilizers, based on their capacity to access nutrients from fertilizers and soil stocks, to fix atmospheric nitrogen, to improve water uptake or to act as bio-control agents. The use of biofertilizers as a supplement has proven to give protection to plant by releasing antibiotics which are capable to fight many plant pathogens. Biofertilizers also protect the plants from salinity and drought stress. They are also economical and safe inputs which provide a wide scope for research in the areas of organic farming and development of stress free environment.
Key findings:
The adoption of biofertilizers as organic replacements for chemical fertilizers is crucial for sustainable farming. Biofertilizers, microbial inoculants, improve soil fertility, enhance nutrient uptake, and protect plants from pathogens, salinity, and drought stress. They are cost-effective, safe, and offer significant potential for research in organic farming and stress management.
What is known and what is new?
Biofertilizers, such as microbial inoculants, offer a promising alternative to chemical fertilizers by improving soil health and plant productivity. While chemical fertilizers have been effective in boosting agricultural yields, they often lead to depletion of soil minerals and reduced fertility. In contrast, biofertilizers help maintain soil structure and fertility, promote nutrient uptake, and protect plants from various stresses such as pathogens, salinity, and drought. They are also cost-effective and environmentally friendly. Furthermore, biofertilizers provide a platform for ongoing research and development in organic farming practices, offering sustainable solutions for future agricultural needs.
What is the implication, and what should change now?
The implication of adopting biofertilizers is significant for agricultural practices. It suggests a shift towards more sustainable and environmentally friendly farming methods. To implement this change, there should be increased awareness and education among farmers about the benefits of biofertilizers. Governments and agricultural organizations should also provide support in the form of subsidies, training, and research funding to encourage the use of biofertilizers. Additionally, there should be a concerted effort to reduce the use of chemical fertilizers and promote the use of organic alternatives.
The rate at which the earth’s natural resources are dilapidating, especially, the reserves of rock phosphate and fossil fuel, is of great concern for the future of agriculture. Agricultural practice is the main consumer of phosphorus in the form of mineral fertilizers. According to Cordell et al. (2009) [1], phosphate fertilizers are mined from only a few rock phosphate deposits in the world and the peak of extraction of phosphate is expected to happen in the 2030s, with the prices expected to increase afterwards due to the higher extraction cost. Fossil fuels are needed to produce nitrogen fertilizers, highly needed for industrial agriculture, by fixing atmospheric nitrogen to ammonia in the Haber-Bosch process.
Apart from the decline of fossil fuels, the use of fossil fuels enriches the atmosphere with fossil CO2. This increase of CO2 has been recognized as the source of change in the change during the 20th century also known as anthropogenic climate change [2]. This global problem has greater implications for developing countries especially in the tropics because weathered soils with nutrient deficiencies and ion toxicities are more common there and then rely more on external inputs to keep up food production. Furthermore people are more likely to suffer food insecurity resulting from the struggles in keeping up with food production [3].
Efforts to mitigate the declining mineral nutrient reserves in the soil are currently major topics of research but the agitation of the global biogeochemical cycles, mainly driven by the use of mineral fertilizers, remains a serious challenge [4]. The nutrients in intensive agriculture are only used in part by the targeted crops, the other part remains in the soil; but the major driver of this perturbance is the part that is lost from the ecosystem, by erosion in case of phosphate, or by leaching in case of nitrogen. When nitrogen fertilizers are applied, the Nitrogen often enters the soil in the form of nitrate. Under low oxygen concentrations in the soil environment, some of the nitrate are denitrified by bacteria which results in Nitrogen and nitrous oxide and is then lost for crop production. Nitrous oxide (N2O) is particularly problematic since it is a "Greenhouse Gas (GHG)", and releasing it into the atmosphere accelerates the depletion of the ozone layer. Another part of nitrate is lost by rainfall which transports and leaches it to the groundwater. As a side effect, lakes or even the sea are “fertilized” causing algal blooms and their subsequent death causes so-called dead zones without any oxygen, important for any life forms, in these water bodies even in large ones like the Baltic Sea or the Gulf of Mexico [5].
The sustainability in agricultural crop production has to reduce the disturbance of the nutrient cycles and find ways to add to the use efficiency of fertilizers, and at the same time protect biodiversity and soil quality. Practices to achieve this have different names like agroecology, organic agriculture or sustainable agriculture, but irrespective of the name, they all have the same goal. Sustainable crop production remains a major global challenge and has drawn increasing attention among policy makers, businesses and the scientific communities [6].
What Are Biofertilizers?
Biofertilizers, also called Microbial inoculants are promising technologies to reduce the use of conventional inorganic fertilizers. Rhizosphere microorganisms are either growing in the rhizosphere or as endophytes inside the roots [7]. Many of them can serve as biofertilizers as they are able to fix nitrogen (N), help to access nutrients such as phosphorus (P) and Nitrogen from organic fertilizers and soil stocks, improve drought tolerance, improve plant health or increase salt tolerance. The discovery of Rhizobia as the first commercial biofertilizer dates back to 1866 which was first patented in 1896 [8].
Since the discovery of the growth promoting effects of Azotobacter and Azospirillum, the systematic research on such rhizobacteria is growing. New species and strains are constantly being discovered and tested, and also their economic importance is increasing. But not only bacteria are being studied, also fungi even yeasts.
Types Of Biofertilizers
Nitrogen Biofertilizers
This group of biofertlizers fixes nitrogen symbiotically. Nitrogen biofertilizers help to correct the nitrogen levels in the soil. Nitrogen is a limiting factor for plant growth because plants need a certain amount of nitrogen in the soil to thrive. Different biofertilizers have an optimum effect for different soils, so the choice of nitrogen biofertilizer to be used depends on the cultivated crop. Rhizobia are used for legume crops, Azotobacter or Azospirillum for non-legume crops, Acetobacter for sugarcane and blue green algae and Azolla for lowland rice paddies.
Phosphorus Biofertilizers
Phosphorus is also a limiting factor for plant growth just like nitrogen. Phosphorus biofertilizers help the soil to reach its finest level of phosphorus and correct the phosphorus levels in the soil. Though, unlike nitrogen biofertilizers, the usage of phosphorus biofertilizers is not dependent on the crops cultivated on the soil. Phosphatika is used for all crops with Rhizobium, Azotobacter, Azospirillum and Acetobacter.
Compost Biofertilizers
Biofertilizers are also used for enrichment of your compost and for enhancement of the bacterial processes that break down the compost waste. Suitable biofertilizers for compost use are cellulolytic fungal cultures and Phosphotika and Azotobacter cultures. A 100% pure eco-friendly organic fertilizer is Vermi Compost; this organic fertilizer has nitrogen, phosphorus, potassium, organic carbon, sulphur, hormones, vitamins, enzymes and antibiotics, which helps to improve the quality and quantity of yield. It is observed that due to continuous misuse of chemical fertilizers, the soil loses its fertility and becomes saline with time. So to overcome such challenges, natural crop boost is the only remedy.
Classifications of biofertilizers
Biofertilizers are classified based on their types, as indicated below:
Nitrogen Fixing Biofertilizers
Increase soil nitrogen level,
Fixes the atmospheric nitrogen in the soil and make it available to the plants.
Examples: Azotobacter, Nostoc, Rhizobium, Azospirillum
Phosphate Biofertilizers: This includes Phosphorous Solubilizing Biofertilizers and Phosphorus Mobilizing Biofertilizers
a) Phosphorus Solubilizing Biofertilizers
i. Solubilize the insoluble phosphate from organic and inorganic phosphate sources
ii. Releases insoluble phosphorus in soil and fix in clay minerals
iii. Secrete organic acids and lower the pH to dissolve bound phosphates in soil.
Examples:
Species of Bacillus, Pseudomonas, Penicillium, Aspergillus
b) Phosphorus Mobilising Biofertilizers
Transfer phosphorus from the soil to the root cortex.
Examples: Arbuscular Mycorrhiza (AM fungi)
Fungus penetrates the cortical cells of the roots,
Increase surface area of roots,
Displaces off absorption equilibrium of phosphate ions which increases the transfer of P ions,
Stimulate metabolic processes,
Arbuscles absorb these nutrients into the root system.
Compost Biofertilizers
Utilize animal dung to enrich soil with microorganisms
Eco-friendly organic fertilizer
Consists of nitrogen, phosphate solubilizing bacteria and various decomposing fungi
Microorganism breaks down organic matter (dead plants, farm yard waste, cattle waste etc).
Examples: Cellulolytic fungi, Azotobacter
Functions of Biofertilizer
Biofertilizers are known to play a number of vital roles in soil fertility, crop productivity and production in agriculture as they are eco-friendly and cannot at any cost replace chemical fertilizers that are indispensable for getting maximum crop yields. Some of the important functions or roles of Biofertilizers in agriculture are:
They supplement chemical fertilizers for meeting the integrated nutrient demand of the crops.
They can add 20-200kg N/ha year (eg. Rhizobium sp 50-100kg N/ha year; Azospirillum, Azotobacter: 20-40kg N/ha /yr; Azolla: 40-80kg N/ha; BGA: 20-30kg N/ha) under optimum soil conditions and thereby increases 15-25 percent of total crop yield.
They can at best minimize the use of chemical fertilizers not exceeding 40-50kg N/ha under ideal agronomic and pest-free conditions.
Application of Biofertilizers results in increased mineral and water uptake, root development, vegetative growth and nitrogen fixation.
Some Biofertilizers (eg, Rhizobium BGA, Azotobacter sp) stimulate production of growth promoting substance like vitamin-B complex, Indole acetic acid (IAA), Gibberellic acids, etc.
Phosphate mobilizing or phosphorus solubilizing Biofertilizers/microorganisms (bacteria, fungi, mycorrhiza etc.) converts insoluble soil phosphate into soluble forms by secreting several organic acids and under optimum conditions they can solubilize/mobilize about 30-50 kg P2O5/ha due to which crop yield may increase by 10 to 20%.
Mycorrhiza or VA-mycorrhiza (VAM fungi) when used as Biofertilizers enhance uptake of P, Zn, S and water, leading to uniform crop growth and increased yield and also enhance resistance to root diseases and improve hardiness of transplant stock.
They liberate growth promoting substances and vitamins and help to maintain soil fertility.
They act as antagonists and suppress the incidence of soil borne plant pathogens and thus, help in the bio-control of diseases.
Nitrogen fixing, phosphate mobilizing and cellulolytic microorganisms in bio-fertilizer enhance the availability of plant nutrients in the soil and thus, sustain the agricultural production and farming system.
They are cheaper, pollution free and renewable energy sources
They improve physical properties of soil, soil tilth and soil health in general.
They improve soil fertility and soil productivity.
Blue green algae like Nostoc, Anabaena, and Scytonema are often employed in the reclamation of alkaline soils.
Bio-inoculants containing cellulolytic and lignolytic microorganisms enhance the degradation/ decomposition of organic matter in soil, as well as enhance the rate of decomposition in compost pit.
BGA plays a vital role in the nitrogen economy of rice fields in tropical regions.
Azotobacter inoculants when applied to many non-leguminous crop plants, promote seed germination and initial vigor of plants by producing growth promoting substances.
Azolla-Anabaena grows profusely as a floating plant in the flooded rice fields and can fix 100-150kg N/ha/year in approximately 40-60 tonnes of biomass produced,
Plays important role in the recycling of plant nutrients.
Production of Biofertilizers
Biofertilizers are the product of fermentation process, constituting efficient living soil microorganisms. They improve plant growth and productivity through supply of easily utilizable nutrients. They are cost effective and eco-friendly bio-inoculants having great potential to enhance agricultural production in sustainable way. Biofertilizers are grouped into different types based on their functions such as nitrogen fixing, phosphate solubilizing, phosphate mobilizing, and other plant growth promoting biofertilizers by different mechanisms.
Solid-state fermentation and submerged fermentation are two main types of fermentation used for the production of biofertilizers. Each type of biofertilizer is prepared by selection of efficient microbial strain, its cultivation using specific nutrient medium, scale-up, and formulation using solid or liquid base. Knowledge about host specificity of the microbial strain and properties of soil and environmental conditions of the field are the important factors which determine the success of biofertilizer application. Recent developments in the field of microbial taxonomy, molecular biology, genetic engineering, metabolic engineering, computer science, and nanotechnology have played a significant role in the advancement of fermentation process of biofertilizer production. Hence, the production of biofertilizers having better efficiency, higher competitive ability, multiple functionality, and longer shelf life has become possible. Biofertilizers with such characteristics can be an effective substitute of chemical fertilizers.
Processes for producing a biofertilizer comprises of the following steps:
Solid State Fermentation (SSF) to produce enzymes and nutrients critical for plant nutrition;
Immobilization through allophane nanoparticles of the enzymes and substrates produced during SSF;
and a Submerged Fermentation to favor the development of microorganisms that improve the quality of the biofertilizer.
Protection is also sought for the biofertilizer that is produced from this process. SSF is started with agricultural, livestock and agro-industrial waste and can be carried out in reactors or piles at a temperature of between 25°C. And 70°C., with a moisture level of between 55% and 80%, and lasts between 12 and 18 days when carried out in reactors and between 5 and 10 weeks when carried out in piles. During Submerged Fermentation, allophane is added in a proportion of between 10% and 40% weight/weight with regard to the dry fermented matter to form enzyme-allophane aggregates that protect the enzymes from microbial degradation, increasing their catalytic efficiency.
Roles of Biofertilizers In Protecting The Soil Environment
Bio fertilizers are helpful for the remediation of polluted soils. They are eco-friendly (environmental friendly), and do not cause pollution unlike inorganic fertilizers which often runoff into water bodies causing eutrophication and methemoglobinemia (blue baby syndrome) when the nitrate level reaches 10mg/L and above. Biofertilizers provides supplement nutrients and microbes that may not be present in soil or that are of less quantity. They reduce the quantity of disposable wastes. Biofertilizers reduces environmental impact of chemical fertilizers especially on soil and water. They help to increase quality of the soil by providing nutrients and natural environment in the rhizosphere. It will aid to decrease nutrient overspill or leaching, along with crop residue management. Microbial inoculants will also aid to lessen the amounts chemical fertilizers use and increase in the use efficiency of the applied fertilizers [9]. The micro-organisms present in biofertilizers are important because they produce nitrogen, potassium, phosphorus and other nutrients required for benefit of the plants. Most biofertilizers also secrete hormones like auxins, cytokinins, biotins and vitamins which are essential for plant growth. Biofertilizers give protection to plant by secreting antibiotics which are effective against many plant pathogens. Biofertilizers also protect plant from salinity and drought stress. Biofertilizers are inexpensive and safe inputs which provide a wide scope for research in the areas of organic farming and development of stress-free environment [10]. Biofertilizers have long lasting effects due to their slow nutrient release. The nutrients from biofertilizers are released to plants slowly and steadily for more than one season. Hence, a long term use of biofertilizer leads to the buildup of nutrients in the soil thereby increasing the overall soil fertility. Additionally, biofertilizers have been found to help control plant diseases such as pythium root rot, rhizoctonia root rot, chill wilt and parasitic nematode
Roles of Biofertilizer in Soil Fertility and Agriculture
Application of biofertilizer results in increased mineral and water uptake, root development, vegetative growth and nitrogen fixation. They can at best minimize the use of chemical fertilizers under agronomy and pest free conditions. They supplement chemical fertilizers for meeting the integrated nutrient demand of the soil. Some biofertilizers stimulate the production of growth promoting substance like Vitamin-B complex, indole acetic acid (IAA), and Gibberellic acid, etc. They act as antagonists and suppress the incident of soil borne plant pathogens, and thus, help in the bio-control of diseases.
Advantages of Biofertilizers over Chemical Fertilizers
They have renewable source of nutrients. They sustain soil health. They act as supplement for chemical fertilizers. They replace 25% - 30% chemical fertilizers. They increase the grain yields by 10% - 40%. They decompose plant residues, and stabilize the C: N ratio of the soil. They help to improve the soil texture, structure and water holding capacity of the soil. They have no adverse effect on plant growth and fertility. They are classified as eco-friendly fertilizers, non-pollutants and cost effective method. They solubilize and mobilize nutrients for both the plant and the soil.
Funding: No funding sources
Conflict of interest: None declared
Ethical approval: The study was approved by the Institutional Ethics Committee of Federal University of Technology Owerri
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