A Comprehensive Review on Biofertilizers: Mechanisms, Applications, and Challenges

Soil degradation, deforestation, and climate change pose significant threats to global food security and ecosystem stability. Land accounts for approximately 29% of Earth’s surface, with 32.7% designated for agriculture and 27% covered by forests. However, agricultural productivity is declining due to intensive farming, excessive chemical fertilizer use, and unsustainable land management practices [1]. Meanwhile, forest degradation caused by deforestation, wildfires, and resource exploitation further exacerbates environmental challenges. The overuse of nitrogen and phosphorus fertilizers has led to soil nutrient depletion, water pollution, and Greenhouse Gas (GHG) emissions [2]. Agriculture alone contributes 55% of total GHG emissions, with methane emissions from rice cultivation reaching 7.66 million metric tons annually. Additionally, nutrient runoff has resulted in widespread eutrophication, depleting oxygen in aquatic ecosystems and causing biodiversity loss [3]. In response to these challenges, biofertilizers have emerged as a sustainable alternative to synthetic fertilizers. Biofertilizers are biological products containing beneficial microorganisms that enhance soil fertility, promote plant growth, and support ecosystem health by facilitating natural nutrient cycling [4]. Unlike chemical fertilizers that supply nutrients directly, biofertilizers stimulate biological processes such as nitrogen fixation, phosphorus solubilization, and organic matter decomposition, making essential nutrients more accessible to plants while improving soil microbial activity [5]. The most widely used biofertilizers include nitrogen-fixing bacteria (Rhizobium, Azospirillum, Azotobacter), phosphate-solubilizing bacteria (Pseudomonas, Bacillus), and mycorrhizal fungi (Glomus species), which form symbiotic or associative relationships with plant roots to enhance nutrient absorption and soil structure [6].

Beyond agriculture, biofertilizers play a crucial role in forestry and ecosystem restoration. They support afforestation, reforestation, and soil reclamation efforts by improving tree survival rates, accelerating nutrient cycling, and enhancing soil rehabilitation in degraded landscapes. Their application in forestry has proven effective in increasing biomass production, restoring biodiversity, and mitigating climate change through enhanced carbon sequestration [7]. Despite their numerous benefits, the large-scale adoption of biofertilizers remains limited due to several challenges. Their effectiveness varies under different environmental conditions, they have a relatively short shelf life, and many farmers and foresters lack awareness of their advantages. Moreover, the complex interactions between biofertilizers and native soil microbial communities necessitate site-specific application strategies tailored to different agroecological zones. Addressing these challenges requires advancements in formulation technology, improved regulatory frameworks, and widespread education on their benefits [8]. This review provides a comprehensive analysis of the science and practical applications of biofertilizers. It explores the different types of biofertilizers, their mechanisms of action, and their impact on soil health and plant productivity. Furthermore, it examines their role in both traditional and modern agricultural systems, their importance in sustainable forestry, and the challenges associated with their application [9]. By synthesizing recent scientific advancements and field studies, this review highlights the current state of biofertilizer technology, identifies future research directions, and underscores their potential in promoting food security while preserving environmental integrity [9].

Ensuring sufficient food production for the world’s growing population while maintaining ecological balance is one of the biggest challenges of the 21st century. Sustainable agriculture has become a global priority, emphasizing not only increased crop yields but also environmental conservation [10]. Over-reliance on chemical fertilizers has led to severe consequences, including soil degradation, water contamination, and disruption of nutrient cycles. Excessive application of synthetic fertilizers reduces soil fertility, alters its water retention capacity, and creates an imbalance in essential nutrients. Furthermore, plants grown with chemical fertilizers and pesticides can accumulate harmful substances, which may pose health risks to humans [11]. The production of chemical fertilizers releases toxic gases such as Ammonia (NH₄), Carbon Dioxide (CO₂), and Methane (CH₄), contributing to air pollution and climate change. Additionally, industrial waste from fertilizer manufacturing is often discharged into water bodies, causing severe contamination [12]. One of the most damaging outcomes is water eutrophication, where excess nutrients promote algal blooms that deplete oxygen levels, leading to aquatic biodiversity loss. Longterm use of synthetic fertilizers also contaminates the soil, reducing its quality and sustainability [13]. Only about half of the nitrogen applied through chemical fertilizers is utilized by crops, while the remainder is lost through volatilization, runoff, or interactions with organic compounds in the soil. Nitrates, a key component of fertilizers, often seep into groundwater and surface water sources, posing serious health risks [14]. High concentrations of nitrates, nitrites, and nitrosamines are linked to conditions such as blue baby syndrome (methemoglobinemia in infants), gastric cancer, goiter, congenital disabilities, heart disease, and further eutrophication of water bodies. The excessive use of chemical fertilizers also contributes to Greenhouse Gas (GHG) emissions, weakening the protective ozone layer and exposing humans to harmful ultraviolet radiation. Agricultural soils account for 60% of human-induced Nitrous Oxide (N₂O) emissions, a greenhouse gas that has 310 times the global warming potential of carbon dioxide [8]. Uncontrolled nitrogen fertilizer application releases Nitrogen Oxides (NO, N₂O, NO₂) into the atmosphere, significantly worsening air pollution. The accumulation of heavy metals such as arsenic and cadmium from chemical fertilizers further threatens human health. If these unsustainable practices continue, long-term soil degradation and loss of beneficial microorganisms could severely impact global food security. To transition toward sustainable agriculture, it is essential to adopt nutrient management practices that are both cost-effective and environmentally friendly. One promising alternative is the use of biofertilizers [9].

Biofertilizers, also known as microbial inoculants, are formulations containing living microorganisms that colonize plant roots and enhance nutrient availability. These beneficial microbes fix atmospheric nitrogen, solubilize phosphorus, and synthesize plant growth-promoting compounds, improving plant health and productivity [15]. Unlike chemical fertilizers, which provide direct nutrient input, biofertilizers work by stimulating biological processes that sustain soil fertility over the long term. By reducing the need for synthetic fertilizers and pesticides, biofertilizers contribute to a healthier and more balanced agricultural ecosystem [16]. Some microbial strains not only facilitate nutrient absorption but also produce essential vitamins and phytohormones that enhance plant growth and resistance to environmental stress [17]. Biofertilizers can be classified based on their mode of action, microbial composition, and intended purpose. Their effectiveness depends on agricultural practices, soil conditions, and environmental factors [18]. Future advancements in biofertilizer technology will be key to achieving sustainable agricultural goals, particularly through biological nitrogen fixation and plant-microbe interactions. Microorganisms also play a crucial role in nutrient cycling, helping maintain ecosystem stability [19]. The microbial community within the soil enhances nutrient availability, uptake, and solubility, making essential micronutrients and macronutrients more accessible to plants [20]. Beneficial bacteria perform several key functions, including:
i. Nitrogen fixation for improved soil fertility.
ii. Phosphorus solubilization to increase plant nutrient absorption.
iii. Phytohormone production, which regulates plant growth and stress responses.
iv. Biological pest control, reducing the need for synthetic pesticides.

As research progresses, biofertilizers will play an increasingly vital role in ensuring sustainable agriculture, reducing environmental pollution, and maintaining soil health. With proper policy support, farmer education, and improved production techniques, biofertilizers can emerge as a viable, eco-friendly alternative to chemical fertilizers, contributing to global food security while preserving natural ecosystems [21] (Figure 1).

Figure 1:Summary of the Manuscript.

The use of biofertilizers in agriculture has gained significant attention due to extensive research on their impact on crop growth. However, their effects on forestry species remain less explored. As agricultural and environmental challenges intensify, biofertilizers are emerging as a viable alternative to synthetic fertilizers, offering a sustainable approach to improving soil health and crop productivity [22].

Mechanisms of biofertilizer action

To fully leverage the potential of biofertilizers, it is essential to understand their modes of action, which include nutrient assimilation, phytohormone regulation, and plant protection. Biofertilizers enhance soil fertility by supplying essential nutrients such as nitrogen, phosphorus, and potassium, preserving the soil’s natural properties while reducing dependence on chemical fertilizers [23].

Plant Growth-Promoting Microorganisms (PGPMs) are classified into three main groups:

a. Arbuscular Mycorrhizal Fungi (AMF)-These fungi establish symbiotic relationships with plant roots, improving water and nutrient absorption [24].
b. Plant Growth-Promoting Rhizobacteria (PGPR)-These beneficial bacteria enhance nutrient uptake, promote root development, and provide resistance against plant pathogens [25].
c. Nitrogen-Fixing Rhizobia-These microbes convert atmospheric nitrogen into forms that plants can easily absorb, boosting plant growth and productivity [26].

Among nitrogen-fixing bacteria, Rhizobium, Azotobacter, and Azospirillum play a crucial role in making atmospheric nitrogen available for plant uptake, thereby reducing the need for synthetic nitrogen fertilizers [27]. Additionally, phosphorus-solubilizing bacteria such as Pseudomonas and Bacillus break down organic and inorganic phosphorus compounds, ensuring optimal nutrient availability for plants. Some biofertilizers, including Azotobacter and Azospirillum, secrete plant growth-promoting compounds that enhance root elongation and nutrient absorption [28]. Furthermore, biofertilizers contribute to hormone production, releasing auxins, gibberellins, and cytokinins, which regulate plant growth, promote flowering, and enhance fruit development. These bioactive compounds play a vital role in stimulating root growth, increasing biomass, and improving overall plant vigor [29]. Beyond nutrient enrichment, biofertilizers provide protection against environmental stressors. They help combat soil-borne diseases by producing antibiotics and antifungal compounds, which suppress pathogenic microbes. Additionally, they assist in reducing heavy metal toxicity by binding and neutralizing harmful metals in the soil, minimizing pollution risks. Some biofertilizers also trigger the production of phenolic compounds, which strengthen the plant’s natural defense mechanisms against pests and diseases [30].

Biofertilizers are an essential component of sustainable agriculture, leveraging the natural capabilities of beneficial microorganisms to enhance soil fertility and plant growth. Unlike chemical fertilizers, biofertilizers rely on living organisms to promote plant health and productivity [31]. Their effectiveness is rooted in well-established biological processes, including nitrogen fixation, phosphorus solubilization, and the enhancement of soil microbiomes. This section delves into the microbial composition of biofertilizers, their mechanisms of action, and their interactions with plants [32].

Microbial composition and functions

Biofertilizers consist of various beneficial microorganisms that actively contribute to soil health and plant nutrition. These microbes establish either direct or indirect interactions with plants, improving nutrient availability and promoting overall plant vigor [33].

Common microorganisms used in biofertilizers: Several key microbial groups are used in biofertilizer formulations, each playing a distinct role in enhancing soil fertility:
a. Rhizobium-A symbiotic nitrogen-fixing bacterium that forms nodules on the roots of leguminous plants. It converts atmospheric nitrogen into a plant-usable form, reducing the need for synthetic nitrogen fertilizers.
b. Azospirillum-A free-living nitrogen-fixing bacterium that associates with the roots of cereals and grasses, promoting root elongation and nutrient uptake [34].
c. Azotobacter-A non-symbiotic nitrogen-fixing bacterium that thrives in the rhizosphere, enhancing soil fertility and producing plant growth-promoting substances.
d. Mycorrhizae-A type of beneficial fungus that forms mutualistic associations with plant roots, increasing water and nutrient absorption, particularly phosphorus [35].
e. Phosphate-Solubilizing Bacteria (PSB)-Microorganisms such as Pseudomonas and Bacillus that break down insoluble phosphate compounds in the soil, making phosphorus available for plant uptake.
f. Potassium-Solubilizing Bacteria (KSB)-Microbes that help release potassium from soil minerals, improving plant growth and stress resistance [36].

Biological processes involved: Biofertilizers function by harnessing natural microbial processes that enhance nutrient availability and soil health. These include:
a. Nitrogen Fixation-The conversion of atmospheric Nitrogen (N₂) into Ammonia (NH₃) by bacteria such as Rhizobium and Azospirillum, providing plants with an essential nutrient for protein synthesis [37].
b. Phosphorus Solubilization-The transformation of insoluble phosphate compounds into bioavailable forms through the action of phosphate-solubilizing bacteria.
c. Potassium Mobilization-The release of potassium from soil particles by potassium-solubilizing bacteria, which helps plants in enzyme activation, photosynthesis, and stress tolerance [38].
d. Production of Growth-Promoting Substances-Many biofertilizer microbes produce hormones such as auxins, gibberellins, and cytokinins that stimulate root development, enhance nutrient uptake, and improve plant growth [39].
e. Biocontrol Activity-Some biofertilizers contain microbes that suppress plant pathogens by outcompeting harmful microorganisms, producing antimicrobial compounds, or inducing plant defense mechanisms [40].

By incorporating these microorganisms into agricultural practices, biofertilizers enhance soil fertility, improve plant health, and reduce dependency on chemical fertilizers.

Mode of action and interaction with plants

Biofertilizers interact with plants in various ways, either by forming symbiotic relationships or by enhancing soil microbial activity through non-symbiotic mechanisms. These interactions play a crucial role in improving nutrient uptake, soil structure, and overall plant resilience [41].

Symbiotic and non-symbiotic mechanisms:

a. Symbiotic Mechanisms-These involve a close, mutually beneficial relationship between plants and microorganisms. For example:
i. Rhizobium forms nodules on the roots of legumes, where it fixes atmospheric nitrogen in exchange for carbon from the plant.
ii. Mycorrhizal fungi penetrate plant roots, extending their hyphae into the soil to absorb phosphorus and other nutrients in return for plant-produced sugars [42].
b. Non-Symbiotic Mechanisms-Some microbes function independently in the soil but still benefit plant growth. For example:
i. Azotobacter fixes atmospheric nitrogen without forming plantroot associations.
ii. Phosphate-solubilizing bacteria release enzymes that convert inorganic phosphate into a form that plants can absorb [43].

Influence on root architecture and nutrient absorption

Biofertilizers significantly influence root development, leading to better nutrient uptake and plant growth. These effects include:
i. Enhanced Root Elongation-Certain biofertilizer bacteria, such as Azospirillum, stimulate root elongation and branching, increasing the plant’s ability to absorb water and nutrients.
ii. Increased Root Surface Area-Mycorrhizal fungi create extensive networks of hyphae that improve nutrient and water absorption, particularly in nutrient-deficient soils [44].
iii. Improved Soil Structure-The microbial activity associated with biofertilizers enhances soil aggregation and porosity, leading to better aeration and water retention [45].
iv. Stimulated Hormone Production-Microbial interactions often trigger the production of plant growth hormones like auxins, which regulate root development and overall plant growth [46].

By fostering these beneficial interactions, biofertilizers not only improve soil fertility but also contribute to more sustainable and resilient agricultural systems.

With the increasing global focus on sustainable farming and integrated nutrient management, biofertilizers are gaining traction, particularly in developing countries. Governments, agricultural institutions, and environmental organizations are actively promoting biofertilizers as an alternative to chemical fertilizers to enhance soil fertility, reduce carbon footprints, and promote climate-resilient agriculture [47]. Despite the growing market demand, biofertilizer adoption remains uneven across regions, primarily due to challenges such as inconsistent efficacy, limited production scalability, short shelf life, and a lack of farmer awareness [48]. While some regions, including China, India, North America, and Europe, have made significant progress in commercial biofertilizer production, many areas still rely heavily on chemical fertilizers due to policy gaps and limited research investments.

To accelerate the transition to biofertilizer-based agriculture, there is a need for:
i. Standardized formulations to ensure consistent effectiveness across different soil types and crops.
ii. Cost-efficient production techniques to make biofertilizers more accessible to farmers.
iii. Regulatory frameworks that encourage biofertilizer innovation and market expansion.
iv. Farmer education and awareness programs to promote largescale adoption [49].

As biofertilizers continue to evolve, they hold immense potential to transform agriculture and forestry by enhancing soil health, reducing environmental pollution, and increasing crop yields sustainably. Strengthening research, policy support, and investment in biofertilizer technology will be key to achieving longterm food security and environmental conservation [50-73] (Table 1).

Table 1:Types of Biofertilizers, Their Mechanisms, and Examples.

The growing global focus on sustainable agricultural and forestry practices has led to a significant rise in the adoption of biofertilizers. As concerns about environmental degradation and soil health increase, there has been a notable shift towards integrated nutrient management strategies [74,75]. This shift has brought greater attention to the benefits of biofertilizers, including Arbuscular Mycorrhizal Fungi (AMF), Phosphorus-Solubilizing Bacteria (PSB), Azospirillum, Azotobacter, Rhizobium, Acetobacter, and even seaweed-based fertilizers [76]. Countries such as China, Canada, Argentina, and several European nations, including Spain, Italy, and Germany, are actively promoting biofertilizer use due to the increasing demand for organic farming and eco-friendly agricultural solutions [77]. Similarly, in the United States, India, and Africa, the awareness of biofertilizers’ role in enhancing soil fertility and crop productivity has grown substantially. The expansion of organic farming worldwide is evident, with the total agricultural land under organic cultivation rising from 69.4 million hectares in 2017 to 74.9 million hectares in 2020. This increase is driven by a greater consumer preference for organic products and sustainable farming techniques [78,79].

Biofertilizers play a crucial role in enhancing soil fertility by acting as seed or soil inoculants, promoting plant growth, and actively participating in the nutrient cycle. Their widespread use in agriculture and forestry is attributed to their ability to replace chemical fertilizers while being cost-effective, environmentally friendly, and capable of improving soil structure and productivity by 10-25% without causing harm to ecosystems [80,81]. In addition to boosting yields, biofertilizers contribute to soil conservation by reducing erosion and enhancing water retention, making them a valuable alternative for long-term agricultural sustainability. Recent research has focused on maximizing the efficiency of biofertilizers by addressing issues such as soil salinization, heavy metal contamination through phytoremediation, and increasing plant resilience to extreme environmental conditions [82,83]. Some of these studies have advanced from laboratory experiments to field trials, demonstrating the potential for large-scale application. Scientists are continuously working on improving biofertilizer technology to reduce production costs, maintain quality, and increase farmer adoption rates [84]. Innovative approaches such as nanotechnology are revolutionizing biofertilizer development. Nano-fertilizers, nano-biofertilizers, and nano-pesticides are emerging as advanced, low-cost, and environmentally friendly alternatives to traditional fertilizers. Additionally [85], highthroughput sequencing is being explored to restore agricultural microbiomes that have been disrupted by unsustainable farming practices. This approach aims to identify and reintroduce beneficial microbes involved in essential soil processes, particularly those related to phosphorus cycling, to create more resilient and productive agricultural systems [86-88] (Figure 2 & 3).

Figure 2:Mechanism of Action Involves in Biofertilizer [85].

Figure 3:Block Diagram Visually Represents How Biofertilizer Inoculation Affects Soil Physicochemical and Biochemical Properties [86].

Biofertilizers play a crucial role in forest ecosystems by enhancing soil fertility, promoting plant growth, and improving resilience to environmental stress. They are an essential component of integrated nutrient management strategies, incorporating nitrogen-fixing bacteria, potassium and phosphorus solubilizers, Plant Growth-Promoting Rhizobacteria (PGPR), ectoand endomycorrhizal fungi, cyanobacteria, and other beneficial microorganisms [89]. These biofertilizers contribute significantly to nutrient and water absorption, helping trees withstand both biotic and abiotic stressors [90,91]. Ectomycorrhizal fungi (ECMF) are particularly vital in forest ecosystems, forming a symbiotic relationship with tree roots through specialized structures such as the Hartig net [92]. This association aids in nutrient cycling, improves soil stability, and contributes to forest restoration efforts. ECMF have proven effective in rehabilitating degraded lands, including sites affected by heavy metal contamination, soil erosion, and wildfires. They also assist in establishing tree plantations by reducing reliance on chemical fertilizers and fostering sustainable forestry practices [93]. With over 7,000 species, ECMF are widely associated with commercially valuable trees such as poplar, birch, oak, pine, and spruce. These fungi facilitate nutrient and water exchange between soil and trees in return for carbon from the plant. ECMF applications have been instrumental in restoring lands damaged by industrial activities, including mining and deforestation [94]. For instance, certain ECMF species, such as Pisolithus albus, have been successfully used to rehabilitate forests affected by mining activities by enhancing tree growth and protecting plants from toxic metal accumulation. ECMF also play a role in restoring forests affected by clear-cut logging [95]. Studies indicate that transferring soil from mature forests to these sites encourages the formation of beneficial microbial communities, improving soil health and aiding tree establishment. Additionally, some ECMF species have demonstrated resilience to wildfires, capturing and transferring nitrogen to surviving vegetation, thus stabilizing the ecosystem post-fire. This makes them valuable tools for reforestation and habitat restoration in fire-prone regions [96].

The invasion of non-native species, such as pine trees in the Southern Hemisphere, has disrupted native forest ecosystems. These invasions are often facilitated by the presence of invasive ECMF species, which outcompete native microbial communities [97]. To counteract this, researchers are exploring the use of non-invasive ECMF strains as biofertilizer inoculants for reforestation efforts, helping maintain ecological balance while still supporting forestry industries [98]. Plant growth is also influenced by microbial communities in the rhizosphere, where PGPRs enhance nutrient availability and promote plant health. These bacteria contribute to processes such as nitrogen fixation, phosphate solubilization, and phytohormone production, which aid in tree growth and stress tolerance [99]. In semi-arid regions, biofertilizers like biochar and PGPRs have been effective in mitigating water stress in tree seedlings, facilitating afforestation efforts in challenging environments. Certain bacterial strains, such as Brevibacillus reuszeri MPT17, have been found to enhance root development and nutrient uptake in tree species like pecan (Carya illinoinensis), while others, including Bacillus paramycoides and Schizophyllum commune, have demonstrated the ability to help trees survive in saline conditions [100]. Cyanobacteria also play a significant role in forest ecosystems, particularly in nitrogen cycling. These microorganisms contribute substantial amounts of nitrogen to boreal forests, forming associations with feather mosses such as Hylocomium splendens and Pleurozium schreberi [101]. By enhancing nitrogen availability in forest soils, cyanobacteria promote tree growth and support overall ecosystem health. Biofertilizer applications in forestry have been linked to improved tree growth, increased yields, and enhanced wood quality [102]. Different biofertilizers exhibit specific benefits; for instance, Azotobacter is highly effective in increasing soil organic matter and nitrogen levels, while Phosphorus-Solubilizing Bacteria (PSB) improve phosphorus and potassium availability, leading to better seedling development [103]. Studies have identified promising microbial isolates, including Lysinibacillus sphaericus, Paenibacillus quercus, Paramyrothecium roridum, and Lysinibacillus fusiformis, which have shown significant potential in enhancing the growth of tree species such as Eucalyptus pellita. Further research is needed to refine these biofertilization techniques and optimize their application in sustainable forestry practices [104]. Forests harbor diverse microbial communities, many of which remain unexplored. Understanding these microbial interactions is essential for harnessing their full potential in forest management and conservation efforts. As research advances, biofertilizers will continue to play an integral role in promoting healthy forest ecosystems and supporting sustainable afforestation projects worldwide [105].

Biofertilizers offer an environmentally sustainable, costeffective, and renewable alternative to chemical fertilizers. However, their widespread adoption faces several obstacles that impact their production, market viability, and practical usage [106]. These challenges include slow action, formulation complexities, sensitivity to environmental conditions such as temperature and moisture, lack of specific microbial strains, inadequate manufacturing facilities, shortage of skilled labor, seasonal demand due to microbial activity, regulatory hurdles, and limited market awareness [107]. The effectiveness of biofertilizers, as seen in various microbial applications, depends on the development of specialized microbial strains, optimized formulations, and reliable field-testing methodologies [108].

Complexity in biofertilizer formulation

The growing interest in biofertilizers has led to the availability of various products worldwide. However, the formulation process plays a crucial role in determining the quality and effectiveness of these biological agents. Preparing biofertilizer inoculants involves multiple steps, including selecting appropriate microbial strains, using suitable carriers, and incorporating additives that support microbial survival during storage, transportation, and soil application [109]. A well-formulated biofertilizer ensures the efficient introduction of beneficial microbes into the target environment, enhancing their functionality upon application. Additionally, affordability remains a key consideration in formulation, requiring the use of cost-effective carriers and organic materials [110]. One of the primary challenges in biofertilizer formulation is the discrepancy between laboratory success and field performance. While some microbial strains show promising results in controlled environments, their effectiveness in realworld conditions can be unpredictable [111]. Manufacturers often combine multiple microbial strains, such as Rhizobia with Arbuscular Mycorrhizal Fungi (AMF) or Phosphate-Solubilizing Bacteria (PSB), to maximize benefits for plants. The physical nature of the carrier material also affects biofertilizer formulation, leading to four major types: solid carrier-based, liquid-based, polymerentrapped, and pressurized dry formulations [112].

Liquid formulations, while easy to apply, often suffer from rapid declines in microbial activity after production. Solid formulations, on the other hand, pose challenges for non-sporulating bacteria, as desiccation can damage cell membranes, leading to microbial death and reduced viability during rehydration [113]. This limitation hinders large-scale commercialization. Although immobilized-cell formulations improve microbial stability, they remain expensive due to the high cost of polymeric carriers, making large-scale production and field application difficult. Additionally, cell mortality is a significant challenge in bio-encapsulation, particularly during drying processes, as limited oxygen transfer affects microbial survival [114]. Another issue with certain formulations, such as fluidized-bed dry formulations, is their short shelf life and susceptibility to contamination due to moisture content in carrier-based inoculants [115]. Contamination by unwanted microorganisms can alter the biofertilizer’s effectiveness, making it essential to maintain sterile production conditions. However, ensuring sterility adds to production costs, making the final product less affordable for farmers [116]. To increase the adoption of biofertilizers, there is a pressing need to develop formulations that are more stable, cost-effective, and tailored to meet agricultural and forestry needs. Advancements in formulation technology should focus on improving microbial survival rates, extending shelf life, enhancing field performance, and maintaining affordability. Addressing these challenges will help maximize the potential of biofertilizers in sustainable forestry and agriculture [117].

Impact of climatic conditions on efficacy

The effectiveness of biofertilizers is significantly influenced by environmental conditions, as microbial inoculants are exposed to various biotic and abiotic stress factors upon soil application [118]. These stressors include competition with native microflora and microfauna, as well as environmental conditions such as soil pH, temperature fluctuations, and salinity. In semi-arid regions, harsh climatic factors such as drought, high salinity, inadequate irrigation, and soil erosion make it difficult for introduced microbial strains to establish and survive. These conditions rapidly deplete beneficial bacteria, reducing the long-term effectiveness of biofertilizers [119]. Microbial strains also face challenges during storage, particularly in peat-based carriers, where temperature fluctuations can affect their viability. Many Gram-negative bacterial strains, which are commonly used in biocontrol and plant growth promotion, exhibit poor tolerance to extreme temperatures and drought [120]. This sensitivity complicates the development of stable bioformulations. For instance, Phosphate-Solubilizing Bacteria (PSB) used in forestry applications must be adapted to withstand cold temperatures if they are to function effectively in subfreezing environments [121]. While psychrotolerant PSB species can remain active in such conditions, their efficiency at room temperature also makes them versatile biofertilizers for a range of environmental conditions. Plant Growth-Promoting Bacteria (PGPB) present additional challenges due to their inconsistent behavior in the field. Their effectiveness varies depending on plant species, environmental conditions, and interactions with native microbial communities [122-124]. Furthermore, large-scale production of certain PGPB strains is difficult, as they often struggle to grow as efficiently in controlled culture systems as they do in their natural habitat. Given the rapidly changing global climate, biofertilizer formulations must be adapted to region-specific conditions to ensure long-term efficacy and sustainability [125,126].

Storage challenges and shelf life

Storage conditions play a crucial role in maintaining the viability and effectiveness of biofertilizers. Factors such as temperature, humidity, and exposure to sunlight significantly impact microbial survival, the quality of carrier materials, and overall product stability. For biofertilizers to remain effective, they must retain a sufficient number of viable microbial cells throughout storage [127]. However, a major challenge is the limited shelf life of live microbial inoculants, which typically lasts between 4 to 6 months when stored at temperatures ranging from 20°C to 25°C. Additional care during storage and transportation is required to prevent microbial degradation, increasing overall production and distribution costs [128]. To maintain biofertilizer potency, proper storage conditions are essential. The recommended storage temperature for extended shelf life is around 4°C, as lower temperatures help preserve microbial viability. For instance, Azotobacter venelandi has been found to retain its viability for up to 90 days at 5°C, while Acinetobacter baumannii remains effective for over six months, exceeding the minimum required viable cell count. However, certain bacterial strains, such as Burkholderia species, show better survival at 28°C, highlighting the importance of strainspecific storage conditions [129]. Before application, biofertilizers stored at 4°C should be acclimated by culturing them at 26°C for at least seven days to allow microbial multiplication and ensure the required cell count is achieved [130]. Proper storage not only ensures biofertilizer effectiveness but also impacts accessibility, as inadequate storage facilities limit product availability in rural areas. Addressing these challenges by improving storage technology, developing more resilient microbial strains, and optimizing formulations for diverse climatic conditions will be essential for the broader adoption of biofertilizers in sustainable agriculture [131].

Impact of climatic conditions on biofertilizer effectiveness

Biofertilizer technology is highly influenced by environmental factors, which can impact its efficacy. The microorganisms in biofertilizers are subject to biotic stress from microflora and microfauna, as well as abiotic stress from soil pH, temperature variations, and salinity. In semi-arid regions, introduced microbial inoculants struggle to survive due to extreme conditions such as drought, high salinity, insufficient irrigation, and soil erosion, which deplete the microbial population quickly [132]. Temperature fluctuations further affect the viability of bacteria, particularly during storage in peat-based carriers. Many beneficial bacterial strains, especially Gram-negative biocontrol bacteria, are highly sensitive to environmental changes, making bioformulation challenging [133]. For example, Phosphorus-Solubilizing Bacteria (PSB) adapted to cold climates are required to function efficiently in subfreezing temperatures, whereas psychrotolerant PSB species that thrive at room temperature are suitable for general applications. However, the effectiveness of Plant Growth-Promoting Bacteria (PGPB) remains inconsistent across different plant species and environmental conditions, often leading to unreliable productivity. Additionally, large-scale production is challenging as many PGPB strains exhibit slow growth in artificial culture conditions compared to their natural habitat. Future strategies should consider region-specific climatic forecasts to enhance biofertilizer performance under changing global conditions [134].

Optimizing storage conditions for biofertilizers

Proper storage conditions significantly impact microbial survival, product longevity, and field efficacy. Key storage factors include temperature, humidity, and exposure to sunlight. The carrier material should ensure the long-term viability of microorganisms and maintain a sufficient number of live cells throughout the storage period [135]. One of the primary challenges with biofertilizers is their limited shelf life, typically around 4-6 months at 20-25°C [136]. Storing them at 4°C significantly extends their viability, with some bacterial strains such as Acinetobacter baumannii maintaining required cell counts beyond six months. Conversely, Burkholderia species show better viability when stored at 28°C for up to two months, highlighting the need for strainspecific storage guidelines [137]. When refrigerated biofertilizers are used, they should be incubated at 26°C for at least seven days before application to reactivate microbial multiplication. Limited access to adequate storage facilities in rural areas often hinders product availability and adoption, making decentralized cold storage solutions a necessary investment for wider implementation [138].

Biofertilizers play a vital role in sustainable agricultural and forestry practices, offering an eco-friendly alternative to synthetic fertilizers. Their application enhances soil fertility, promotes plant growth, and aids in environmental conservation [139]. Biofertilizers can be applied through various methods, including seed inoculation, root dipping, and direct soil application in dry or liquid form. In seed inoculation, biofertilizers are mixed into a slurry and evenly coated onto sterile seeds before drying and planting [140]. The root-dipping technique is primarily used for transplanted crops, where plant roots are submerged in a biofertilizer solution before transplantation. Alternatively, biofertilizers can be applied as a foliar spray or soil treatment at the appropriate planting stage [141]. Despite their benefits, several obstacles hinder widespread adoption. Biofertilizers often perform inconsistently in the field compared to controlled environments due to variable climate, soil composition, crop type, and biodiversity. They also require more time to colonize roots and enhance plant growth compared to synthetic fertilizers, which deliver immediate results [142]. Challenges include limited awareness among farmers about the ecological advantages of microbial biofertilizers, inadequate promotion by agricultural extension services, lack of suitable carrier materials for formulation, and insufficient storage infrastructure. Moreover, inadequate labeling regarding expiration dates and microbial composition raises doubts about product authenticity [143], further affecting acceptance among farmers. This section explores the practical use of biofertilizers in sustainable agriculture, forestry, and ecosystem restoration, along with the most effective field application methods [144].

Use in sustainable agriculture

The adoption of biofertilizers in sustainable agriculture is increasing due to their ability to improve crop productivity while minimizing environmental impact. By enhancing soil health and reducing dependence on chemical fertilizers, biofertilizers contribute to organic farming and sustainable crop production systems [145].

Organic farming practices

Biofertilizers are widely used in organic farming, where chemical fertilizers and pesticides are restricted. Their role in organic agriculture includes:
i. Improving soil fertility-Biofertilizers enhance nutrient cycling, maintaining long-term soil productivity without depleting natural resources.
ii. Reducing chemical inputs -The use of biofertilizers minimizes synthetic fertilizer application, reducing soil and water contamination.
iii. Enhancing plant health-Many biofertilizers contain microbes that suppress plant pathogens and improve crop resistance to diseases.
iv. Supporting biodiversity-The introduction of beneficial microbes into the soil improves microbial diversity, fostering a balanced ecosystem [1,146].

Crop-specific applications

Different crops benefit from specific biofertilizers based on their nutrient requirements and growth conditions. Some key applications include:
i. Cereals (Rice, Wheat, Maize, etc.)-Azospirillum and Azotobacter are commonly used to enhance nitrogen fixation and promote root growth. Phosphate-solubilizing bacteria improve phosphorus uptake, leading to higher yields [147].
ii. Legumes (Soybean, Peas, Lentils, etc.)-Rhizobium is essential for nitrogen fixation in leguminous plants, improving their growth and reducing the need for nitrogen fertilizers.
iii. Vegetables (Tomatoes, Carrots, Spinach, etc.)-Mycorrhizal fungi and potassium-solubilizing bacteria enhance nutrient absorption, leading to improved quality and productivity [148].

The targeted use of biofertilizers in different cropping systems ensures maximum efficiency, leading to sustainable and profitable agricultural production.

Role in forestry and ecosystem restoration

Biofertilizers are increasingly recognized for their role in forestry and ecosystem restoration, where they help in soil improvement, afforestation, and the rehabilitation of degraded lands.

Benefits in afforestation and soil reclamation

i. Enhancing Tree Growth-Mycorrhizal fungi significantly improve nutrient uptake in forest tree species, leading to better establishment and growth in degraded lands.
ii. Improving Soil Structure-The use of biofertilizers increases soil aggregation, organic matter content, and microbial activity, making soils more fertile and resilient [149,150].
iii. Rehabilitating Degraded Lands-In areas affected by deforestation, mining, and erosion, biofertilizers accelerate soil recovery and support the re-establishment of native plant species.
iv. Enhancing Carbon Sequestration-Biofertilizers contribute to carbon sequestration by increasing plant biomass and promoting soil organic matter accumulation, helping mitigate climate change [151].

Case studies on forest tree growth

Several studies demonstrate the effectiveness of biofertilizers in forestry:
a. Case Study 1: Mycorrhizal Inoculation in Pine and Eucalyptus Plantations
i. Forest nurseries inoculated with mycorrhizal fungi showed a significant increase in seedling survival rates and biomass production.
b. Case Study 2: Rhizobium Application in Acacia and Albizia Species
i. Nitrogen-fixing bacteria improved tree growth and soil nitrogen levels in reforestation projects, reducing the need for chemical fertilizers.
c. Case Study 3: Phosphate-Solubilizing Bacteria in Mangrove Restoration
i. The introduction of phosphate-solubilizing microbes enhanced root development and nutrient uptake, improving mangrove establishment in degraded coastal zones [152].

These examples highlight how biofertilizers can be integrated into forestry projects to enhance sustainability and ecosystem recovery.

Field application methods

The effectiveness of biofertilizers depends on their proper application. Various methods can be used to ensure optimal plantmicrobe interactions and maximize benefits.

Seed treatment

a. Biofertilizers are applied as a coating on seeds before planting to enhance early root colonization.
b. Commonly used for legumes with Rhizobium and cereals with Azospirillum.
c. Improves seed germination, root development, and nutrient uptake.
d. Application Method:
i. Mix biofertilizer powder or liquid with a sticking agent (e.g., sugar solution) before applying to seeds.
ii. Allow seeds to dry in shade before sowing [153,154].

Soil inoculation

a. Direct application of biofertilizers to soil improves microbial populations and nutrient availability.
b. Suitable for phosphate-solubilizing bacteria, potassiummobilizing bacteria, and mycorrhizal fungi.
c. Enhances soil structure, organic matter content, and nutrient cycling.
d. Application Method:
i. Mix biofertilizer with compost or organic manure before applying to soil.
ii. Apply around the root zone to ensure effective colonization [155,156].

Foliar application

a. Some biofertilizers can be applied as a liquid spray on plant leaves to enhance nutrient uptake and stress resistance.
b. Particularly useful for microbial bio-stimulants that produce plant growth hormones.
c. Application Method:
i. Dilute biofertilizer solution as per recommended concentration.
ii. Spray evenly on foliage during the early morning or late afternoon to maximize absorption [157].

Best practices and dosage recommendations

To maximize the benefits of biofertilizers, the following best practices should be followed:
a. Use Fresh and Viable Biofertilizers-Ensure biofertilizers are stored under appropriate conditions and used before their expiry date.
b. Apply Under Favorable Conditions-Optimal soil moisture, temperature, and pH levels enhance microbial activity [158].
c. Combine with Organic Matter-Adding compost or farmyard manure improves microbial survival and effectiveness.
d. Follow Recommended Dosage-Overuse can lead to microbial imbalances, while underuse may not yield expected results [159].

Expanding market value and growth of biofertilizers

With increasing global awareness of sustainable agriculture, the demand for biofertilizers has surged. Consumers, particularly in developing nations, are increasingly prioritizing organic farming, contributing to the expansion of the biofertilizer market. Developed countries such as Spain, Italy, and Germany have also experienced rising demand [160]. The global biofertilizer market was valued at approximately $1.88 billion in 2022 and is projected to reach $3.51 billion by 2027, growing at a Compound Annual Growth Rate (CAGR) of 13.2% [161]. Legume-based nitrogen-fixing inoculants dominate the sector, accounting for around 78% of the market, with phosphate-solubilizing and other bioinoculants comprising 15% and 7%, respectively. India ranks as the fourth-largest consumer of potassium bioinoculants, following the United States, China, and Brazil [162]. North America leads the global market, followed closely by Europe and the Asia-Pacific region. South America is emerging as a key player in the industry. The increasing emphasis on sustainable agriculture and food security continues to drive biofertilizer market expansion worldwide [163].

Although biofertilizers are gaining global recognition, further research is needed to enhance their field efficacy. Understanding how beneficial bacteria interact with plant microbiomes is crucial for optimizing their performance under various soil conditions. Researchers should focus on biofertilizers’ ability to modify and enhance the natural microbial ecosystem in plants, leading to improved plant growth and resilience [164]. A significant research gap exists in the study of biofertilizers for forest ecosystems. While coniferous species have been studied to some extent, data on deciduous trees remain scarce. Additionally, many laboratory and greenhouse findings have yet to be successfully translated into field applications. Future studies should explore high-efficiency inoculant strains that can adapt to diverse soil conditions and plant species. Investigating the physiology of rhizobacteria under different soil conditions through in vitro and in vivo studies is essential [165]. Cutting-edge research methods, such as molecular analysis, microbial engineering, biotechnology, and functional genomics, should be leveraged to monitor bacterial colonization and their evolutionary adaptation post-inoculation [166]. Metagenomics, meta transcriptomics, and meta proteomics can provide deeper insights into plant-microbe interactions and their role in plant development. Additionally, genetically engineered strains of plant growth-promoting bacteria have shown promising potential, yet public skepticism regarding their environmental safety remains a barrier to adoption [167]. Researchers and policymakers should work toward educating the public on the safety and advantages of these biofertilizers. Furthermore, biofertilizers should be optimized to sustain microbial life in harsh soil environments while maintaining economic feasibility [168]. Another emerging area is the role of plant prebiotics in biofertilizer efficiency. These compounds act as signaling molecules that attract beneficial bacteria to plant roots. Future research should focus on developing microbial consortia that optimize plantmicrobe interactions for increased agricultural productivity [169]. Establishing a global database of biofertilizer efficacy across various environmental conditions, soil types, and growing seasons would aid in refining application strategies. Moreover, studies have shown that integrating biofertilizers with reduced synthetic nitrogen applications can maintain yield while lowering fertilizer costs [170]. In particular, the JUNCAO nitrogen-fixing biofertilizer has demonstrated improved crop vigor, soil nutrient enhancement, and cost savings. Moving forward, integrating multi-omics approaches with biofertilizer technology can further improve agricultural productivity, ensuring sustainable food production for a growing global population [171].

Biofertilizers offer a sustainable path toward enhancing agricultural productivity while preserving soil health and reducing reliance on synthetic fertilizers. Despite their potential, widespread adoption is limited by challenges such as inconsistent performance, short shelf life, and limited awareness among farmers [172]. Addressing these issues requires advancements in microbial strain selection, formulation techniques, and storage methods to ensure stability and effectiveness. Moreover, a deeper understanding of microbial ecosystems can aid in developing tailored biofertilizers suited to diverse agricultural contexts. Future research should focus on creating efficient delivery systems to support large-scale applications, including reforestation efforts [173]. Embracing biofertilizers is crucial for building a resilient agricultural system that promotes food security, environmental sustainability, and long-term ecosystem health [174-182].

All the authors have substantial (equal) contribution in compilation of this review chapter. All authors have read and approved the final manuscript.

Being a review article, no funding was involved in compilation of the information in this review chapter.

The authors declare that they have no competing interests.

This study does not involve experiments on animals or human subjects.

This study did not require extensive data collection. For additional information on the subject, the corresponding author can be contacted.

The journal maintains a neutral stance regarding jurisdictional claims associated with the authors’ institutional affiliations.

We express our sincere gratitude to my supervisors at Ahmadu Bello University, Zaria, Kaduna State, Nigeria, for their critical review and valuable suggestions, which have significantly enhanced the quality of this manuscript.

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