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American Journal of  
Life Science and Innovation (AJLSI)

Microbial Inoculants in Agriculture: A Microbiological Review from A Nigerian
Perspective

Ewubare P. O.1*, Omokaro G. O.2, Ewansiha O. C.1, Edosa J. O.1

Volume 2 Issue 3, Year 2023
ISSN: 2833-1397 (Online)

DOI: https://doi.org/10.54536/ajlsi.v2i3.2241
https://journals.e-palli.com/home/index.php/ajlsi

Article Information ABSTRACT

Received: November 07, 2023

Accepted: December 03, 2023

Published: December 06, 2023

Chemical compounds are absorbed by most crops from the soil. Several synthetic fertilizers 
contain acid radicals, such as hydrochloride and sulfuric radicals, thus increasing soil acidity 
and adversely affecting soil and plant health. Some plants can also absorb highly recalcitrant 
compounds. Continuous consumption of  such crops can lead to systematic disorders in 
humans. A reliable alternative to the use of  chemical inputs is microbial inoculants, which 
can act as biofertilizers, bioherbicides, biopesticides, and biocontrol agents. Microorganisms 
are capable of  promoting plant growth, and controlling pests, diseases, and weeds. Microbial 
inoculants are beneficial microorganisms applied either to the soil or the plant to improve 
productivity and crop health. These natural-based products are widely used to control pests 
and enhance soil and crop quality, thereby benefiting human health. Microbial inoculants 
consist of  a blend of  microorganisms that work with the soil and its inhabitants to improve 
soil fertility and health, ultimately benefiting human health. They have the ability to minimize 
the negative impact of  chemical inputs, thereby increasing the quantity and quality of  farm 
produce. This review paper summarizes the effects of  microbial inoculants on agricultural 
soil in Nigeria by examining relevant works related to the topic. To achieve this, databases 
such as Google Scholar, Frontier in Microbiology, African Journals Online (AJOL), Scopus, 
Web of  Science, ScienceDirect, and Directory of  Open Access Journals (DOAJ) were 
explored to identify studies on the effects of  microbial inoculants on agricultural soil in 
Nigeria.

Keywords

Nigeria, Microbial Inoculants, 
Review, Soil Microbes, 
Biofertilizer

INTRODUCTION
Soil microorganisms can enhance plant growth and 
safeguard soils from diseases and environmental stresses 
(Glick, 2012). These microorganisms form partnerships 
with plants, promoting growth through beneficial traits 
such as providing nutrients via biological nitrogen fixation 
(BNF) and phosphate solubilization, as well as reducing 
stress through the regulation of  1-aminocyclopropane-
1-carboxylate deaminase expression and the production 
of  phytohormones and siderophores, among other 
mechanisms (Alori, 2016). Introducing these helpful 
microbes into the soil and plants, a process known as 
inoculation, is a less harmful and more environmentally 
friendly approach compared to using chemical fertilizers. 
Microbial inoculation technology is considered a 
sustainable agricultural practice, leading to reduced 
production costs. There is a growing trend in the use 
of  symbiotic or free-living nitrogen-fixing bacteria in 
sustainable agricultural systems (Koki & Takayoshi, 
2013). Research conducted by Omokaro et al. (2023) 
in Delta State, Nigeria, focusing on the perspective of  
smallholder farmers, it was noted that 47.6% of  these 
farmers utilize chemical pesticides such as Gammalin for 
the control of  pests and diseases. Utilizing inoculants is 
particularly appealing as it significantly decreases the need 
for chemical fertilizers and pesticides, and there is a rising 
availability of  commercialized inoculants for various 

crops (Babalola 2010; Babalola & Glick 2012). The use 
of  microbial inoculants has proved to be a promising 
technology to obtain an increase in food production and 
a sustainable agricultural system. The effects of  microbial 
inoculants on agricultural soils include the introduction 
of  soil microbes such as bacteria and fungi. However, 
this paper reviews research on the effects of  microbial 
inoculants in agricultural soils in Nigeria and its impact 
on plants and soil.

METHODOLOGY
A literature review was carried out to identify the relevant 
articles published. The earliest research publication 
concerning the review was found in 2006. Google 
Scholar, Frontier in Microbiology, African Journals 
Online (AJOL), Scopus, Web of  Science, Science 
Direct and Directory of  Open Access Journals (DOAJ) 
databases were explored to identify studies on organic 
amendment effect on soil fertility in Nigeria using the 
following keywords in English; ‘microbial inoculants use 
in Nigeria’, ‘effect of  microbial inoculants in Nigerian 
agriculture’, ‘effect of  microbial inoculants in soil and 
plants in Nigeria. A total of  150 articles were identified in 
the initial review but 20 articles were selected to be a good 
match for the review study based on the objective of  the 
study and geographical location. Figure 1 below shows 
the system search method.

1 Department of  Soil Science and Land Management, University of  Benin, P.M.B 1155, Ugbowo, Benin City, Edo State, Nigeria
2 Institute of  Ecology, People’s Friendship University of  Russia, Miklukho Maklaya 6, Moscow, Russia
* Corresponding author’s e-mail: paulewubare9@gmail.com



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DISCUSSION
Microbial Inoculants in Agriculture
Microbial inoculants are formulations containing 
beneficial microorganisms crucial for maintaining 
sustainable agriculture in soil ecosystems. They serve as 
an eco-friendly option, potentially replacing chemical 
fertilizers and pesticides (Babalola & Glick, 2012). These 
inoculants consist of  active microorganism strains that 
directly or indirectly enhance microbial activity, improving 
nutrient mobility in the soil. They can function as 
phyto-stimulants, bio-fertilizers, or microbial biocontrol 
agents, offering protection against various pathogens 
and acting as effective bio-herbicides (Babalola, 2010). 
Additionally, naturally occurring microbes obtained from 
the wild and applied to plants can also serve as bio-
herbicides (Babalola, 2007; Alori et al., 2017). Given the 
growing global population and the consequent need to 
boost agricultural production, maintaining soil fertility 
is crucial. Biofertilizers, comprising active microbes, 
present a viable technology to enhance food production 
without endangering human and environmental health. 
These biofertilizers encompass organisms that supply 
or facilitate the availability of  different nutrients to 
plants, including nitrogen fixers, phosphorus solubilizers, 
potassium solubilizers, sulfur solubilizers, mycorrhiza, 
and more (Pathak & Kumar, 2016; Alori et al., 2017).

The Effects of  Microbial Inoculants in Soil
In the process of  seed and soil inoculation, a large number 
of  efficient and viable microbial cells are introduced 
into the soil to rapidly colonize the host rhizosphere. 
However, this introduction can significantly disrupt the 
balance of  soil microbial communities (Babalola, 2014). 
When using microbial inoculants, substantial quantities 
of  microbial cells are introduced into the competitive 
soil environment. For instance, biocontrol Pseudomonas 
inoculants that produce 2,4-diacetylphloroglucinol 
(Phl) are introduced into the rhizosphere community 
in significant amounts, preventing the proliferation of  
specific fungal pathogens. Azospirillum spp. produce 

relatively high levels of  indole-3-acetic acid (IAA), which 
enhance the formation of  plant lateral and adventitious 
roots, improving mineral and nutrient uptake. While 
introduced microbes may temporarily alter the equilibrium 
in the rhizosphere community, the bacterial community 
structure often rebounds due to ecosystem resilience. 
Compounds like indole-3-acetamide, indole-3-pyruvate, 
indole-3-acetaldehyde, and 4-chloroindole-3-acetic acid 
have been found to exhibit auxin activity (Roesti et al., 
2006; Olanrewaju et al., 2017).
Biological nitrogen fixation comprises both symbiotic 
nitrogen fixation and free-living nitrogen-fixing systems. 
Symbiotic nitrogen-fixing genera include Rhizobium, 
Achromobacter, Sinorhizobium, Azoarcus, Mesorhizobium, 
Frankia, Allorhizobium, Bradyrhizobium, Burkholderia, 
Azorhizobium, and Herbaspirillum (Babalola, 2010). 
Phosphorus (P) is a vital element essential for plant 
growth and development, second only to nitrogen. In 
soil, P exists in organic and inorganic forms that are 
not readily available to plants. However, several Plant 
Growth-Promoting Rhizobacteria (PGPR) have been 
identified to mobilize poorly available phosphorus 
through solubilization and mineralization. Examples 
include Pseudomonas spp., Agrobacterium spp., Bacillus 
circulans, Azotobacter spp., Bacillus spp., Burkholderia spp., 
Enterobacter spp., Erwinia spp., Kushneria spp., Paenibacillus 
spp., Ralstonia spp., Rhizobium spp., Rhodococcus spp., Serratia 
spp., Bradyrhizobium spp., Salmonella spp., Sinomonas spp., 
and Thiobacillus spp. (Azziz et al., 2012; Alori et al., 2017). 
Atmospheric nitrogen fixation and mineral solubilization, 
such as phosphorus (P), are direct mechanisms through 
which microbial inoculants exert their influence. In 
indirect growth promotion, microbial inoculants impact 
plants by inducing systemic resistance (ISR) or systemic 
acquired resistance (SAR), enhancing disease resistance 
(Babalola, 2010).
Biotic and abiotic stress such as insect and nematode 
damage, drought or flood, presence of  metals, chemicals 
(both organic and inorganic), ultraviolet light, extreme 
temperatures, mechanical wounding as well as fungal 

Figure 1: Flow chart showing the methodology of  review of  literature



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Am. J. Life Sci. Innov. 2(3) 39-43, 2023

and bacterial pathogens triggers increased production 
of  ethylene in plants (Ali et al., 2014). Biocontrol PGPR 
that produces HCN can also synthesize some cell wall 
degrading enzymes or antibiotics. HCN can also act as an 
anti-fungi agent. HCN synthesized by PGPR is usually in 

small quantity, this ensures that the fungi do not develop 
resistance to the synthesized antifungal thereby enhancing 
the effectiveness of  antifungal in soil (Kundan et al., 2015; 
Olanrewaju et al., 2017).

Table 1: Some examples of  the use of  microbial inoculants in agriculture
Microbial Location Result and Findings References
Rhizobium and Bradyrhizobium 
strains

Ahmadu Bello University, 
Zaria, Nigeria

Produced more shoot and nodule dry 
weight

N’cho et al., 
(2015)

Rhizobacteria inoculant 
(Nodumax legume inoculant)

Enugu State University of  
Science and Technology, 
Nigeria

Increased leaf, stem and root dry 
weight of  Bambara groundnut. 
Increased number of  root nodules, 
fresh pods of  Bambara groundnut and 
soil total Nitrogen content

Ikenganyia 
et al., (2017)

Bradyrhizobium Ahmadu Bello University, 
Zaria, Nigeria

Increased soil organic carbon, total 
nitrogen and carbon to nitrogen ratio

Omeke, 
2017

Arbuscular mycorrhizae fungi Federal University of  
Agriculture, Abeokuta, 
Ogun State, Nigeria

Increased Arbuscular mycorrhizae root 
colonization in soybean and maize

Yusif  and 
Hayatu, 
2017

Colletotrichum coccodes Olabisi Onabanjo 
University, Ogun State

Control of  velvetleaf  (Abutilon 
theophrasti) 

Babalola, 
2007

Azospirillum and 
Mazospiriflo-2 (Azospirillum 
brasilense, Strain)

Shanono, Ibadan The combined inoculant reduced N 
accumulation in the shoot biomass of  
maize

Laditi et al., 
2012

Alternaria Olabisi Onabanjo 
University, Ogun State

Weed control Babalola, 
2009

The Effects of  Microbial Inoculants on Plants
The success of  microbial inoculation depends largely on 
the following: the plant species and cultivar, soil type, 
soil moisture and temperature conditions, the number 
of  pathogens present in the soil around the plant and 
how the inoculants were prepared and applied (Babalola 
et al., 2007). In Nigeria, a study tested the effect of  
microbial inoculants and foliar fertilizers application on 
promiscuous soybean (TGx 1448-2E) under smallholder 
farmers’ conditions in the northern Guinea savanna, of  
Nigeria. Three microbial inoculants; Bradyrhizobium 
spp. (RACA 6), arbuscular mycorrhizal fungi (Rhizatech) 
and Trichoderma harzianum (Eco-T) and two foliar 
fertilizers; Agroleaf  high P and Agolyser were used. Grain 
yield was relatively increased by the application of  RACA 
6 + TSP, RACA 6 + Agrolyzer and RACA 6 + Rhizatech 
+ Agrolyser compared to the control. The authors 
suggested that soybean co-inoculation with rhizobial or 
fungal inoculants and/or foliar fertilizers could lead to 
improved grain yields (Ncho et al., 2013).
A similar study was conducted for screening of  15 
commercial and laboratory rhizobium inoculants in 
Kadawa (Sudan savanna) and Samaru (northern Guinea 
savanna) to identify effective and promising products on 
a promiscuous soybean genotype (TGx 1448-2E) and a 
Malaysian genotype (SAMSOY-2). More so, an application 
of  three commercial products and seven strains resulted 
in increased nodulation relative to the control in Kadawa, 

while two commercial products and six strains increased 
nodulation, but only two strains resulted in significant 
increases in biomass and/or grain yield. The authors 
recommended 1495 MAR, USDA 4675, USDA 110, 
TSBF 531 and TSBF 560 as effective inoculants to 
consider for improved grain yield in Samaru (Yusuf  et al., 
2012). More so, Omeke, (2017) noted that, Integration 
of  inoculated soybean with rhizobium in the maize-
based cropping systems in combination with N fertilizer 
application promotes higher carbon sequestration (stock) 
and soil N as compared to other treatments combination.
A study was conducted in Awka Anambra state, Nigeria 
to determine the suitability of  decomposed rice husk, 
charcoal and coal to act as carrier materials for cowpea 
Bradyrhizobia inoculants, using TAL 209, TAL 379 and 
TAL 173 strains imported from US. The study showed 
decomposed rice husk as better carrier materials. A 
follow up pot experiment also confirmed the ability of  
Bradyrhizobia in decomposed rice husk to nodulate, 
increase shoot dry matter and total N in cowpea in 
different soils relative to uninoculated controls (Okereke 
and Okeh, 2007). Inoculation trials were also conducted 
on Eutric Cambisols (EC) and Rhodic Nitisols (RN) soils 
in a greenhouse study. Soybean (TGx 1448-2E), cowpea 
(IT90K-277-2) and groundnut (SAMNUT 21) were used 
as test crops along with rhizobia inoculants (MAR 1495, 
TSBF Mixture, Legumefix, HiStick and IRj 2180A) to 
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symbiotic relationship with the crops. Rhizobia strains 
MAR 1495 and TSBF mixture showed similar ability to 
improve the productivity of  soybean and groundnut and 
thus recommended for use as common inoculants for the 
two crops (Aliyu et al., 2013).
Furthermore, the influence of  rhizobia inoculation on 
N-fixation by cowpea (Vigna unguiculata (L.) Walp.), 
groundnut (Arachis hypogaea L.) and bambara groundnut 
(Vigna subterranea L.Verdc.) was evaluated under field 
condition in Maiduguri, Sudano-Sahelian zone of  Nigeria. 
Strains isolated from the same crops the previous year 
were used to inoculate them the next year. The results 
showed rhizobia inoculation to increase the amount of  
N- fixed by 46% over the control. Cowpea fixed 42.68 
kg N ha-1 while groundnut and bambara groundnut fixed 
27.19 and 32.53 kg N ha-1, respectively. This indicates 
a higher potential of  cowpea to alleviate soil nitrogen 
deficiency over the other legumes, particularly where the 
indigenous rhizobia nodulating the crops are inadequate 
(Yakubu et al., 2010).

CONCLUSION
In Nigeria, the use of  chemicals in agriculture can be 
avoided and thus they can be removed from human 
diets and minimize the reduction of  environmental 
hazards. Pest and weed control can be achieved by 
employing microbial inoculants as biocontrol agents and 
bio-herbicides. Harnessing natural resources including 
beneficiary microorganisms is one of  the most effective 
approaches to improving farm productivity and food 
quality in a sustainable way. Microbial inoculant as part 
of  agricultural practices will ensure healthy food security 
for the future population. Several findings of  microbial 
inoculants have been shown to improve soil properties, 
crops growth, biotic and abiotic stress and nutrient intake 
and further improve health living between microorganisms 
and plant in the root region. However, these findings are 
not restricted to Nigeria alone and have necessitated the 
need to adopt microbial inoculants in other regions of  
the world. However, with the bulk of  farmers in Nigeria 
being unlettered and majority uneducated, it could be 
challenging to change their mindset and convince them 
of  probable alternatives to the use of  inoculants as a 
means of  bio-fertilizers.

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