The Role of Biofertilizers in Modern Agriculture: Advancements,

Applications, and Future Prospects

1. Introduction

Definition and significance of biofertilizers

A biofertilizer is a substance which contains living microorganisms which when applied to seeds,
plants, or soil, colonizes the rhizosphere or the interior of the plants and promotes plant growth
by increasing the supply of nutrients to the host plant (Vessey 2003; Bardi and Malusà 2012;
Malusa and Vassilev 2014). Biofertilizers are widely used to accelerate those microbial processes
which augment the availability of nutrients that can be easily assimilated by the plants. They
improve soil fertility by fixing the atmospheric nitrogen and solubilizing insoluble phosphates
and produce plant growth-promoting substances in the soil (Mazid and Khan 2015). Beneficial
microorganisms in biofertilizers accelerate and improve plant growth and protect plants from
pests and diseases (El-yazeid et al., 2007) These biofertilizers have been promoted to harvest the
naturally available biological system of nutrient mobilization which enormously increases soil
fertility and ultimately, crop yield (Pandey and Singh 2012) They are cost-effective and can be
used as a supplement to chemical fertilizers. Microorganisms like bacteria, fungi and blue-green
algae are used as biofertilizers and to increase their shelf-life they are packed in carrier materials
like peat and lignite powder. In this regard, biofertilizers have paramount significance in
sustaining agricultural productivity and healthy environment [3].

DOI 10.1007/s11356-016-8104-0

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The role of biofertilizers in sustainable agriculture
By increasing population of the world, the demand for the food is increasing rapidly (1,2). The
food demand is increasing in those developed countries where the land resources are not
contributing part in crop production as the population need in daily bases needs the food
requirements.to increase this capacity of land to produce more production the people first move
to the application of chemical fertilizers which increase crop production. But the long application
of chemical fertilizers shows adverse effects on the environment (1,3,4). These chemicals
accumulate in the water and also can the cause of eutrophication (2,3) These chemicals also harm
the soil fertility, decrease Holding capacity of soil, increases the salinity and disparity in soil
nutrients (1) So the intention goes towards the bio fertilizers. These were used to decrease the
bad impacts of low fertility on the soil, the impact of environmental stress and the effect of biotic
stress such as pathogens and other microorganisms. (5–7). In this aspect many works have done
in this field so many organic fertilizers have been introduced in these years. These work as the
natural stimulators of plant growth and the development of the plants (8–10) important group of
organic fertilizers were made on the basis of plant growth promoting microorganisms (PGPM).
There are many groups of the microorganism which are beneficial for the plants but the major
contribution is of the following three which considered as important for plants growth:
arbuscular mycorrhizal fungi (10,11). Plant growth promoting rhizobacteria, and nitrogen fixing
bacteria that are not considered as PGPR(4,10) The main interest going towards the application
of these bio fertilizers are because of increase capacity of the nutrient uptake of the plants and he
increase society of the society.(10,13).
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Comparison with chemical fertilizers

General use of chemicals as a fertilizers can full fell the demand of fast growth and high amount
of food supply but obviously those leads to damage the environment (damaging microbial biota,
killing friendly insects and increase in pH). However, the use of chemicals fertilizers makes the
crops susceptible to disease and also results in decease soil fertility (5,20) The world population is
projected to reach 8.5 billion in 2030, and to increase further to 9.7 billion in 2050 and 10.4 billion by
2100. To feed the world population we have to increase the amount of agriculture and increase
the productivity in such a way the it is useful and also show no bad effect on either environment,
Human, beneficial insects etc. for this purpose we have to increase agriculture productions using
chemical fertilizers, pesticides, herbicides, fungicides, and insecticides (22) As already discussed
due to hazardous effect we are moving towards other sources rather the chemicals which have to
be more safe and more effective and ecologically safe and cost effective as well, all these
properties are present in bio-fertilizers (23). The bio-fertilizers like other man-made chemicals
are commercial products having beneficial microbes, substances important for growth of
microbes and other additives which can probably increase the growth of microbes. It was
reported that bio-fertilizer increase the contents of food protein, amino acids, vitamins, and
nitrogen and other essential elements from renege 10%- 40% (24) The bio-fertilizer provides and
help the plant getting both macro and micro essential elements for growth and also help in supply
of hormones and other organic element for plants (25) The application of bio fertilizer is most
effective and natural way to keep the bio system active and working, the microbes in soil
provides nutrients to plants and helping the biodiversity maintains by improving the quality of
soil (26)

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(https://www.un.org/en/global-issues/population#:~:text=The%20world%20population%20is
%20projected,and%2010.4%20billion%20by%202100. )

Types of Biofertilizers

Nitrogen-Fixing Biofertilizers

Nitrogen is one of the major important nutrients very essential for crop growth. Atmosphere
contains about 80 percent of nitrogen volume in Free State. The major part of the elemental
nitrogen that finds its way into the soil is entirely due to its fixation by certain specialized group
of microorganisms. Biological Nitrogen Fixation (BNF) is considered to be an important process
which determines nitrogen balance in soil ecosystem. Nitrogen inputs through BNF support
sustainable environmentally sound agricultural production. The value of nitrogen fixing legumes
in improving and higher yield of legumes and other crops can be achieved by the application of
biofertilizers (Kannaiyan, 2002). Biological nitrogen fixation is one way of converting elemental
nitrogen into plant usable form (Gothwal et al., 2007). Nitrogen-fixing bacteria (NFB) that
function transform inert atmospheric N2 to organic compounds (Bakulin et al., 2007). Nitrogen
fixer or N fixers organism are used in biofertilizer as a living fertilizer composed of microbial
inoculants or groups of microorganisms which are able to fix atmospheric nitrogen. They are
grouped into free-living bacteria (Azotobacter and Azospirillium) and the blue green algae and
symbionts such as Rhizobium, Frankia and Azolla (Gupta, 2004). The list of N2-fixing bacteria
associated with non legumes includes species of Achromobacter, Alcaligenes, Arthrobacter,
Acetobacter, Azomonas, Beijerinckia, Bacillus, Clostridium, Enterobacter, Erwinia, Derxia,
Desulfovibrio, Corynebacterium, campylobacter, Herbaspirillum, Klebsiella, Lignobacter,
Mycobacterium, Rhodospirillum, Rhodo-pseudomonas, Xanthobacter, Mycobacterium and
Methylosinus (Wani, 1990).

BACTERIAL BIOFERTILIZERS FOR SUSTAINABLE CROP PRODUCTION: A REVIEW

Rhizobium

These are nitrogen-fixing rhizobacteria and belong to the family of Rhizobacea. It includes
Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, and Mesorhizobium. They have
mutualistic association with leguminous plant roots and those which are free living fix the
nitrogen in non-leguminous plant are known as diazotrophs (50) It is not a simple process either
complex of enzyme are involved in it i.e. Nitrogenase which contains Di Nitrogenase reductase
containing (Fe) iron and molybdenum (Mo) as a cofactor (51) It convert N2 into to NH3 by
using electrons and also oxygen is essential for respiration of Rhizobium sp.(4) There are three
different kinds of Nitrogenase complexes depending upon changes in cofactor of di Nitrogenase
Mo- Nitrogenase, V- Nitrogenase and Fe- Nitrogenase (52) Some genes are involved in the N2
Fixation which are called ‘Nf’genes they are essential for nitrogen fixation in free-living &
nitrogen-fixing organism (53) The Nif genes are involved in the activation of Fe/Mo cofactor and
also for the electron donation, biosynthesis of cofactors, and functioning and regulatory of
enzymes.(54) Experiments show that when plants were inoculated with the strain of Rhizobium
wild type strain Retile 68% more nirtogenase activity was seen, 25-30% increasing in leaf
substances and seeds resultant was increase up to 16%. (55) Abeles et al 2012 also showed that
when rhizobium sp was applied so the ethylene level was also inease which is one of the major
plant regulators and also help in inhibiting of rhizobia infection.

doi:10.20944/preprints202003.0262.v1

Azotobacter

They are the photoautotrophic, aerobic, non-symbiotic free-living bacteria belong to the family
azotobacteriaceae, playing very important role in nitrogen cycle of plant. They are present where
soil is alkaline and most commonly arable soil (58) Azotobacter vinelandii, Azotobacter
beijerinckii, Azotobacter insignis,and Azotobacter macrocytogenes are the common sp of
Azotobacor . (21) 30 Reported that Different type of hormones i.e. gibberellins, naphthalene
acetic acid is produced by these bacteria which prevent the formation of root pathogen but
enhance the root growth by minerals and nutrients uptake by plant. Vitamins such as vitamin B
complex is also produced by these bacteria. These type of bacteria are found in different type of
crops such as rice, maize, sugarcane, vegetables (Azobactor play important role in production of
some other vitamins such as riboflavin and thiamin (59)

doi:10.20944/preprints202003.0262.v1

Azospirillum

They are the photoautotrophic, aerobic, non-symbiotic free-living bacteria belong to the family
azotobacteriaceae, playing very important role in nitrogen cycle of plant. They are present where
soil is alkaline and most commonly arable soil (58) Azotobacter vinelandii, Azotobacter
beijerinckii, Azotobacter insignis,and Azotobacter macrocytogenes are the common sp of
Azotobacor . (21) 30 Reported that Different type of hormones i.e. gibberellins, naphthalene
acetic acid is produced by these bacteria which prevent the formation of root pathogen but
enhance the root growth by minerals and nutrients uptake by plant. Vitamins such as vitamin B
complex is also produced by these bacteria. These type of bacteria are found in different type of
crops such as rice, maize, sugarcane, vegetables (Azobactor play important role in production of
some other vitamins such as riboflavin and thiamin (59)

doi:10.20944/preprints202003.0262.v1

Cyanobacteria

Azolla contain sp Azolla caroliniana, Azolla microphylla, Azolla filiculoides, and Azolla
mexicana (21). These are present in large amount in paddy field belonging to eight different
types of families and enhance the growth of plant by producing different type of hormones such
as Indole acetic acid, Gibberellic acid (21). To increase the productivity Nitrogen is essential
mineral for that and that nitrogen is provided to rice plant by means of biological nitrogen
fixation (4,60) 4-5% of nitrogen is present in Azolla on dry basis and 0.2-0.4% is present on wet
basis. Azolla is very important means of organic fertilizer as it provide nitrogen to rice plant (21)
It also has the ability to decompose the soil fastly and also provide the plant important minerals
like phosphorus, potassium iron, zinc and other micro elements, (61)

doi:10.20944/preprints202003.0262.v1

Phosphate-Solubilizing Biofertilizers

Phosphate solubilizing microorganisms (PSMs) are bacteria or fungi that are capable of breaking
down insoluble forms of phosphorus, such as phosphates, in the soil and making it available to
plants as a soluble form that can be easily absorbed (Figure 1) (Rawat et al., 2020). They are
huge category of beneficial microbe including many genera for in
stance Bacillus spp., Pseudomonas spp., Streptomyces spp., Aspergillus spp., Rhizobium spp. Fu
sarium spp., Trichoderma spp., Penicillium spp., Serratia spp., Micrococcus spp., Stenotrophomo
nas spp., Acinetobacter spp., and Agrobacterium spp. (Rodrı́guez and Fraga, 1999). This process
increases the overall availability of phosphorus to plants, leading to improved plant growth and
crop yields. PSMs are commonly found in soil and rhizosphere, and play an important role in
nutrient cycling and soil fertility (Beheshti et al., 2022). PSMs have had several applications in
biotechnology. For instance, in the pharmaceutical and food industries, PSMs are used to
produce antibiotics, vitamins, and other bioactive compounds (Sekurova et al., 2019);
furthermore, PSMs have the potential to play a role in the development of new and efficient
bioprocesses for the sustainable production of biofuels and other bio-based products (Osanai et
al., 2015). The most well-known uses of PMSs are in agricultural and environmental
engineering. For their outstanding nature described above, PMS are used for improving soil
fertility in agriculture, enhancing plant growth and tolerance against stress of instance salinity
(Luo et al., 2022), nutrient deficiency (He et al., 2022; 2021; Chen et al., 2022a) etc.,; and hence
increasing crop yields (Chen et al., 2022b); they can also be used for bioremediation along or
combining with plants, to remove for instance heavy metals from contaminated soil and water
(Pinilla et al., 2008; Chen et al., 2019a).

https://doi.org/10.3389/fbioe.2023.1181078

PSMs can regulate plant metabolism by providing an increased availability of soluble

phosphorus. This increased availability of phosphorus can lead to changes in plant growth and
metabolism (Rodrı́guez and Fraga, 1999), such as an increased rate of photosynthesis, improved
root development, and an enhanced ability to defend against stressors such as drought or disease
(Billah et al., 2019; Kour et al., 2020). PSMs can enhance plant endogenous gene expression and
help plants cope with abiotic stress by providing an increased availability of soluble phosphorus.
This increased availability of phosphorus can activate signaling pathways and trigger the
expression of stress-responsive genes in plants, which can enhance their ability to tolerate and
resist environmental stressors such as drought, salinity, heavy metal toxicity, and temperature
extremes. For example, research has shown that PSMs can increase the expression of genes
involved in the regulation of water uptake, antioxidant defense, and heat shock response, which
can help plants better cope with abiotic stress (Paul et al., 2017). In addition, PSMs can also
stimulate the production of phytohormones such as auxins, cytokinin, gibberellins et al., which
can enhance plant growth and stress tolerance

Potassium-Solubilizing Biofertilizers

Potassium is the third most important major essential plant nutrient after nitrogen and
phosphorus. It has a key role in plant metabolism that triggers most important enzymes involved
in the plant physiology. The deficiency of potassium hinders plant physiology leading to poor
growth and development and lesser yields (White and Karley 2010). This also disturbs the
immune system of plants that increases susceptibility to diseases (Armengaud et al. 2010) and
pest attack (Troufflard et al. 2010). Potassium occurs in soil as available, fixed, interlayer, and
mineral K. The application of potassium fertilizers is a contemporary practice to supply available
K in extensive agricultural systems (Yadegari et al. 2012; Dasan 2012; Zhang et al. 2013). The
potash fertilizers that are available in the world market are costly that increase the cost of inputs
and decrease the agricultural profitability. The bacteria that are involved in the solubilization of
potassium from K-bearing minerals are called potassium-solubilizing bacteria (KSB). They have
the ability to convert insoluble/mineral K into available K in soil (Zeng et al. 2012). KSB in the
soil and rhizosphere play a central role in the cycling of K (Diep and Hieu 2013). They solubilize
the K-bearing minerals by producing acids (Basak and Biswas 2012). Soilplant-microbe
interaction is an important aspect of recent research. The K solubilizers are important part of
microbial community in soil especially in the rhizosphere and play an important role in plant
growth through solubilization of K-bearing minerals. Most of the farmers only use N and P
fertilizers. They are ignoring K fertilizer as they are either unaware of the importance of K
fertilizer or the price of these fertilizers are too high that these are out of reach of resource for
poor farmers (Mohammadi and Sohrabi 2012). The available K is, therefore, decreasing in soils
due to more removal of crops than application of fertilizers. In this situation, the role of KSB is
gaining importance in modern agriculture for sustainable crop production. These bacteria release
K from insoluble minerals (Basak and Biswas 2009; Archana et al. 2012; Parmar and Sindhu
2013; Prajapati et al. 2013; Gundala et al. 2013). These bacteria are also beneficial for plant
growth promotion through providing protection from plant pathogens and protecting them from
stress conditions. A considerable number of these bacteria are present in the rhizosphere and
improved plant growth by a number of mechanisms (Nadeem et al. 2013; Glick 2014)

Potassium-Solubilizing Bacteria and Their Application in Agriculture

Plant Growth-Promoting Rhizobacteria (PGPR)

Plant growth-promoting rhizobacteria (PGPR) are the benefcial crowd of rhizosphere

microorganisms that can increase the plant growth through various processes such as nutrient
uptake, synthesis of siderophore, phytohormone synthesis, N2 fixation by the living organisms,
solubilization of insoluble phosphorous, introduction of systemic tolerance genes, synthesis of
ACC deaminase, various volatile organic compounds (VOC), etc. The PGPR utilization is
potentially increased in sustainable farming because of its eco-friendly and practical nature to
substitute the increasing usage of synthetic nutrients and insecticides. Rhizobacteria produce a
large number of substances that affect plant growth promotion through a direct or indirect way.
The use of commercial biofertilizers containing best PGPR strains is increasing rapidly, and for
this reason, the importance for the search of PGPRs and their mode of action is increasing day by
day (Bhattacharyya and Jha 2012)

Bhattacharyya and Jha (2012) observed that the substances made from living bacteria and fungi,
when inoculated to the soil or seedling roots make colonization in the inner sections of the plants
or in the rhizosphere, thus enhancing plant growth and development. Vessey (2003) reported that
the PGPR strains like Rhizobium, Mesorhizobium, Azorhizobium, Bradyrhizobium, etc. have the
capability to act as biofertilizers. Two primary types of relationship are found between the PGPR
and their host: (1) endophytic and (2) rhizospheric. The relationship in which PGPR lives inside
the host plants is called an endophytic relationship. He also proved that endophytes are present in
the apoplastic intercellular places of the parenchyma tissue. PGPR increase the fertility in the
rhizosphere through fve different areas like enhancing nutrient status in the exceptional vicinity
of roots, BNF, promoting useful symbiosis of the host plants, expanding the root surface area and
the combination of all the above mechanisms of action. McCully (2001) stated that PGPR could
colonize plant roots in the rhizosphere relationship. The capacity of PGPR colonizing to the plant
roots in soil rhizosphere is mainly affected by the soil pH and plant exudation Different types of
PGPR produce different phytohormones like cytokinins, IAA, etc. which can change the root
structure and enhance the plant growth (Kloepper et al. 2007). PGPR producing IAA and
gibberellins in rhizosphere soil play an essential function in enhancing the number of root tips
and increasing the root surface area in several herbaceous plants (Han et al. 2005). Werner et al.
(2003) explained the increase in root surface area, root initiation, cell division, and cell
enlargement through increased growth of lateral and adventitious roots by the use of PGPR-
formulated cytokinins.

https://doi.org/10.1007/978-3-030-48771-3_11

Mycorrhizal Biofertilizers

Types (e.g., AMF - Arbuscular Mycorrhizal Fungi) and benefits

Microbial inoculants, including arbuscular mycorrhizal (AM) fungi and plant growth-promoting
rhizobacteria, are potential components of sustainable management systems (Adesemoye and
Kloepper 2009). AM fungal inoculants are marketed as an important biological component to
commercial horticulture and agriculture, but for successful application of AM fungi with
economically profitable results, the soil environment must be suitable for the development of the
AM fungal symbiosis (Baar 2008).

Companies have taken different market approaches for microbial inoculants, ranging from
products with AM fungi alone to mixed products (Baar 2008). In order to exploit beneficial
effects of AM fungi in sustainable agriculture, appropriate management practices have to be
applied (Vosa´tka and Albrechtova 2009). By better understanding mycorrhizal symbioses for
optimization of plant– soil systems, the need for biofertilizers that include inoculants of AM
fungi in agricultural production will be clarified.

https://doi.org/10.1007/978-3-662-45370-4_4
 2.6. Other Emerging Biofertilizers

Biochar, vermicompost, and organic biofertilizers

3. Mechanisms of Action

 3.1. Nutrient Solubilization and Mobilization

o Mechanisms of nutrient availability enhancement
 3.2. Biological Nitrogen Fixation
o Process and importance in agriculture
 3.3. Phytohormone Production
o Influence on plant growth and stress tolerance
 3.4. Disease Suppression
o Biocontrol properties and mechanisms
 3.5. Soil Structure Improvement
o Role in soil health and fertility

4. Applications in Agriculture

 4.1. Role in Sustainable Agriculture

o Enhancing soil fertility and crop yields
 4.2. Biofertilizers in Organic Farming
o Contribution to organic farming practices
 4.3. Integration with Conventional Farming
o Synergies with chemical fertilizers and integrated nutrient management (INM)
 4.4. Case Studies and Success Stories
o Examples of successful biofertilizer applications in various crops

5. Challenges and Limitations

 5.1. Production and Formulation Challenges

o Stability, shelf-life, and mass production
 5.2. Environmental and Soil Conditions
o Factors affecting biofertilizer efficacy
 5.3. Adoption Barriers
o Farmer awareness, accessibility, and cost
 5.4. Regulatory and Quality Control Issues
o Standards and regulations governing biofertilizers

6. Future Perspectives

 6.1. Innovations in Biofertilizer Technology

o Advances in formulation, delivery systems, and microbial consortia
  6.2. Potential for Climate Change Mitigation
o Role in reducing greenhouse gas emissions and enhancing carbon sequestration
 6.3. Integration with Precision Agriculture
o Use of biofertilizers in precision farming and digital agriculture
 6.4. Global Market Trends and Future Opportunities
o Market growth, research trends, and emerging markets

7. Conclusion

 Summary of key points

 The importance of biofertilizers in sustainable agriculture
 Final thoughts on the future role of biofertilizers in global food security

8. References

 Comprehensive list of sources and literature cited throughout the review