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Current IssueSpecial IssueEditorial BoardOnline First ArticlesArchive

Full Research Article

Development and Evaluation of a Liquid Bio-inoculant Consortium for Enhancing Growth and Productivity of Redgram in the North-Eastern Zone of Tamil Nadu

R
R. Brindavathy1
G
G. Porkodi2,*
M
M. Gnanachithra3
P
P. Sivasakthivelan4
B
B. Karthikeyan5
K
K. Parameswari6,*
R
R. Abirami7
1Department of Agricultural Microbiology, Oilseeds Research Station, Tindivanam-604 102, Tamil Nadu, India.
2Department of Soil Science and Agricultural Chemistry, Agricultural College and Research Institute, Pudukkottai-622 104, Tamil Nadu, India.
3Department of Agricultural Microbiology, TNAU, Coimbatore-641 003, Tamil Nadu, India.
4Sugarcane Research Station, Cuddalore-607 001, Tamil Nadu, India.
5Department of Agricultural Microbiology, Agricultural College and Research Institute Chettinad, Sivagangai-630 102, Tamil Nadu, India.
6Department of Seed Science and Technology, Forest College and Research Institute, TNAU, Mettupalayam, Coimbatore-641 301, Tamil Nadu, India.
7Department of Natural Resource Management, Horticulture College and Research Institute, Periyakulam, Theni-625 604, Tamil Nadu, India.

  • Submitted27-08-2026|

  • Accepted05-10-2026|

  • First Online 17-10-2026|

  • doi 10.18805/LR-5717

ABSTRACT

Background: Pigeonpea [Cajanus cajan (L.) Millsp.] is a protein-rich, drought tolerant pulse crop, cultivated in tropical and subtropical regions in India. Integrated crop management practices like balanced nutrients, bioinoculant and organic supplements would increase the redgram productivity. Liquid bioinoculants are preparations of living microorganisms in liquid formulation that increases soil vitality, fertility and productivity, as when applied to seeds, soil or plant surfaces. Multi-strain or microbial consortia with suitable combinations of beneficial microorganisms have evolved as cost effective components of sustainable agriculture. Hence research was planned to develop a consortium with redgram specific Rhizobium, Bacillus megaterium var. phosphaticum and Paenibacillus mucilaginosus (KRB-9).

Methods: In vitro studies were carried out to evaluate the compatibility and shelf life of the consortium. Two-year field experiment was taken to study the effect of consortium on redgram with variety VBN 3. Bioinoculants were applied in form of seed treatment @ 125 ml ha-1 seeds and soil application @ 500 ml ha-1. Consortium and individual application was applied separately to evaluate their effects. The experiment comprised of nine treatments and 3 replications. The results of two years pooled values were revealed under investigation.

Result: Among the treatments examined, highest plant height, biomass production, grain yield (1237 kg ha-1) and benefit-cost ratio (2.62) was observed when 75 per cent recommended fertilizer dose together with seed treatment and soil application of microbial consortium was used. This treatment was effective and inexpensive approach for sustainable red gram production.

INTRODUCTION

Redgram [Cajanus cajan (L.) Mill sp.] also known as pigeon pea is an important pulse crop cultivated in the tropical and subtropical regions of the world predominantly in India. It is an important source of dietary protein for a large section of vegetarian population. Additional to its high nutritional property, this legume plays a substantial role in soil fertility by biological nitrogen fixation (Kenzong et al., 2025) and most suited for sustainable agriculture (Fanish et al., 2023). Worldwide, India ranks first in red gram cultivable area and production and contributes major share in National pulse production and nutritional security (Hansen et al., 2020). Rhizobium have symbiotic association with redgram and endophytically occupies the nodules and fixes atmospheric nitrogen (Mula and Saxena, 2010). Moreover, the root architecture of this dicot, improves soil physical and chemical properties viz., soil structure, water infiltration, accumulation of soil organic matter (Ade et al., 2018).
       
Though, redgram has ecological benefits, productivity is very low in India. One of the major constraints is the disproportionate and excessive use of chemical fertilizers, which deteriorates soil health, reduces nutrient use efficiency and increases production costs. While, continuous use of chemical fertilizers without organic or biological inputs leads to decrease in soil microbial activity and nutrient cycle mechanisms. Moreover, Tamil Nadu has the lowest area of 0.04 million ha with low production (0.05 million tonnes) and moderate productivity 1,039 kg/ha (Udgata et al., 2025) . The area and productivity has to be maximized to meet the redgram demand. Hence Bioinoculants and organic inputs are safe substitutes for chemical fertilizers. As a long duration pulse crop, bacterization with beneficial microorganism facilitates nutrient availability and increases the yield (Nosheen et al., 2021). Therefore, balanced nutrient management, involving judicious use of agrochemicals, increased use of organic amendments and integration of bioinoculants are necessary for enhancing soil fertility and crop yield in redgram cultivation.
       
Bioinoculants are preparations of living microorganisms increases the rehabilitation and rejuvenation of soil vitality, as when applied colonize the rhizosphere or plant tissues and promotes the plant growth by increasing the nutrients availability through the mechanisms such as nitrogen fixation, nutrient solubilization, mobilization and recycling and helps in the maintenance of soil fertility and productivity (Riaz et al., 2020; Vessey, 2003; Pindi and Satyanarayana, 2012).  The utilization of bioinoculants has been employed for several decades and has been scientifically validated with crop-specific strains. Of late, multi-strain biofertilizers or microbial consortia with suitable combinations of beneficial microorganisms have evolved as important components of sustainable agriculture (Keshta, 2008). These microbial consortia help in plant growth, soil fertility enhancement and biological management of soil-borne diseases (Mousa et al., (2022).
       
In India, liquid biofertilizers have emerged as a proven technology because of their unique production procedures and excellent properties. such as higher microbial population density, longer shelf life (more than one year), lower risk of contamination, ease of handling and transportation, lower production costs and compatibility with mechanized agriculture (Thompson, 1980) and hence gaining popularity. Studies on the application of liquid microbial consortia in redgram are limited. Hence a research was planned to develop a consortium, specifically for redgram to evaluate its effect on biometric parameters and yield attributes of red gram.

MATERIALS AND METHODS

In vitro studies
 
Standard bioinoculants were utilized for the development of the consortium. Rhizobium (redgram specific CC1), Bacillus megaterium var phosphaticum (PS 2) and Paenibacillus mucilaginous (KRB-9) were cultivated in their respective nutritional broths. Rhizobium was cultivated in Yeast Extract Mannitol Broth -YEMA broth (Subba Rao, 1983) phosphobacteria in nutrient broth (Brindavathy and Shenbagavalli, 2021) and Paenibacillus mucilaginous in modified Alexandrov’s broth (Ben-David and Davidson, 2014). For consortium formulation the three-log phase bacterial cultures (23.2x109 CFU; 11.5x109 CFU and 17.3x109 CFU of Rhizobium, PSB and KRB respectively) were mixed in equal proportion and the individual cultures were preserved for comparative analysis. All the inoculated cultures were preserved for one year to examine their shelf life, population density and to evaluate the specific characteristics of each inoculum. Fifteen replications of each inoculum were maintained to draw samples.  Aliquots were periodically collected to enumerate the population by serial dilution and plating methods (CIMMYT, 1988). 
 
Field experiments
 
Geographical location of the experimental site
 
The field experiments were conducted during the rabi seasons from 2023 to 2025 at the Oilseeds Research Station, Tindivanam, Tamil Nadu, situated at 12°21' N latitude, 79°66' E longitude and an altitude of 45.6 m above sea level. The soil type is sandy loam. The initial soil analysis at the experimental site were 21.6% coarse sand, 29.3% fine sand, 28.5% silt and 24.2% clay, medium organic carbon content (0.63%), low available nitrogen levels (242 kg ha-1), high available phosphorus concentrations (33.7 kg ha-1) and medium available potassium content (215 kg ha-1).
 
Field layout and the application of inputs
 
The field was thoroughly ploughed to fine tilth. The experiment composed with nine treatments with Randomized Block Design (RBD), each replicated three times. The red gram variety VBN 3 was sown with a row spacing of 45 x 90 cm. The biofertilizer strains Rhizobium (CC1), Phosphate Solubilizing Bacteria (PSB-1) and Potassium Releasing Bacteria (KRB-9) were used separately and in various consortium combinations according to the treatment schedule. The treatment structures were as follows: T1 - 100% NPK; T2 - 100% NPK with seed treatment of Rhizobium and PSB; T3 - 75% NPK with seed treatment of Rhizobium and PSB; T4 - 100% NPK with seed treatment of consortium; T5 - 75% NPK with seed treatment of consortium; T6 - 100% NPK with seed treatment and soil application of Rhizobium and PSB; T7 - 75% NPK with seed treatment and soil application of Rhizobium and PSB; T8 - 100% NPK with seed treatment and soil application of consortium; T9 - 75% NPK with seed treatment and soil application of consortium. The treatments were imposed by seed treatment with liquid biofertilizer inoculants at a rate of 125 mL ha-1 of seed quantity. The biofertilizer cultures were combined with farmyard manure (FYM) and applied at a rate of 500 mL ha-1 in accordance with the treatment plan.
 
Data collection and sample processing
 
Biometric observations namely plant height, number of branches, nodule number per plant and plant biomass were recorded at 45th DAS. Yield attributes viz., number of pods per plant and yield per ha were recorded. Soil samples were collected initially and at the time of harvest for soil nutrient analysis. Plant samples and seeds were collected to assess the nutrient content. The data collected were statistically analysed.
 
Statistical analysis
 
Analysis of variance (ANOVA) was performed using the SAS software, Bartlett’s Chi-square test, Aitken’s square root transformation, PROC GLM procedure were used for analysis. The graphs were developed using the STAR IRRI package (International Rice Research Institute, Philippines).
 
Economics
 
The experimental data for the two years were examined using standard methods formulated by CIMMYT to work out the economics (Bashan et al., 2023). The market prices of the inputs during 2025-2026 were used for calculating the budget.

RESULT AND DISCUSSION

In vitro studies: shelf-life studies and consortium compatibility
 
Compatibility and shelf-life of rhizobium in individual and consortium formulations
 
The population dynamics of Rhizobium in both individual and consortium formulations were observed at 30 days interval for up to 360 days after incubation (DAI) (Fig 1). A significant reduction in the cell population was noted during the storage duration in both formulations. The individual Rhizobium culture consistently exhibited a somewhat greater population than the consortium formulation.

Fig 1: Shelf life of Rhizobium in individual and consortium inoculations during storage.


       
The initial population of Rhizobium was 53.6 x 109  CFU ml-1 in the individual culture and 51.2 x 109  CFU ml-1 in the consortium. Following 30 days of storage, the population decreased slightly to 49.0 x 109  and 46.7 x 109  CFU ml-1, respectively. A gradual decline in cell viability was noted, recording 27.33 x 109 CFU ml-1 for the individual inoculum and 16.33 x 109 CFU ml-1 for the consortium at 300 DAI. At the end of the storage duration (360 DAI), the Rhizobium population exceeded 109 CFU ml-1 in both formulations, measuring 19.42 x 109 CFU ml-1 in the individual inoculum and 14.64 x 109 CFU ml-1 in the consortium.
       
The minor decline in Rhizobium population under consortium circumstances may be ascribed to competition for resources and space among the microbial partners. Nonetheless, the preservation of viable populations exceeding the minimal suggested level after one year of storage unequivocally illustrates the compatibility of Rhizobium with phosphobacteria and potassium-releasing bacteria in the consortium formulation. Previous studies (Malusá and Vassilev, 2024).) reported analogous findings, indicating that multi-strain inoculants frequently display somewhat reduced individual populations owing to microbial interactions, although retain adequate viability for field application.
 
Shelf-life of phosphobacteria in individual and consortium formulations
 
The shelf life of phosphobacteria diminished progressively during the storage duration in both individual and consortium formulations (Fig 2). The individual phosphobacterial culture exhibited greater population than the consortium at all sampling intervals. The initial phosphobacterial population was 52.5 x 109 CFU ml-1 in the individual culture and 42.5 x 109 CFU ml-1 in the consortium. Subsequent declines were noted at 360 DAI, with populations attaining 20.54 x 109 CFU ml-1 in the individual culture and 12.72 x 109 CFU ml-1.

Fig 2: Shelf life of phosphobacteria in individual and consortium inoculations during storage.


       
Notwithstanding the decrease in viable counts, phosphobacteria sustained populations exceeding 109  CFU ml-1 for the whole storage duration. The shelf life of phosphobacteria exceeds more than a year demonstrates the suitability for liquid carrier medium and the compatibility among consortium members. Similar findings have been reported (Basak et al., 2021), noting the prolonged survival of phosphate-solubilizing bacteria in liquid biofertilizer formulations throughout extended storage durations.
 
Shelf-life of potassium-releasing bacteria in individual and consortium formulations
 
Similar results were found in KRB also (Fig 3). The initial population of KRB was 44.3 x 109  CFU ml-1 in the individual culture. Following 30 days of storage, the population stabilized at around 41.45 x 109 CFU ml-1 before experiencing a slow drop. At 300 DAI and 360 DAI, the population attained 20.86 x 109  and 18.82 x 109  CFU ml-1, respectively. The sustained presence of KRB populations above 109 CFU ml-1 after 360 days demonstrates exceptional shelf-life and formulation stability. The results align with previous findings that documented extended lifespan of potassium-solubilizing bacteria in liquid biofertilizer formulations under ambient storage conditions (O’Callaghan,  2023; Alori et al., 2017).

Fig 3: Shelf life of potassium-releasing bacteria in individual and consortium inoculations during storage.


 
Functional traits for liquid bioinoculants consortium and individual bioinoculants
 
The phosphate-solubilizing capacity of phosphobacteria was assessed using plate assay and broth culture methods. Notable differences were noted between individual PSB inoculation and consortium inoculation regarding solubilization efficiency and inorganic phosphorus (Pi) emission. The individual PSB culture generated a greater solubilization zone diameter (1.6 cm) compared to the consortium (1.1 cm). Thus, the solubilization efficiency was significantly greater in the individual inoculation (207.69%) than in the consortium (120.00%). The development of an expanded halo zone surrounding the colony signifies increased secretion of organic acids and phosphatase enzymes that facilitate the dissolution of insoluble phosphate compounds in the medium. Similar findings was reported by Pan et al., (2021) registered that proficient phosphate-solubilizing bacterial strains demonstrated enhanced halo zone development attributed to heightened acidity of the surrounding medium and successful mineral phosphate solubilization.
       
The solubilization of inorganic phosphorus in Pikovskaya’s broth augmented with the incubation duration in both treatments. The individual PSB culture exhibited Pi solubilization values of 35.20, 55.60 and 62.74 µg ml-1 at 7, 14 and 21 days after inoculation, respectively, yielding a mean value of 51.18 µg ml-1. The consortium inoculation recorded values of 38.40, 45.20 and 45.80 µg ml-1 at the respective intervals, with a mean of 43.13 µg ml-1 (Table 1). While the consortium demonstrated marginally elevated phosphorus solubilization at 7 days after inoculation (DAI), the individual PSB culture exceeded the consortium’s performance at 14 and 21 DAI, signifying its superior phosphate-solubilizing efficacy. The primary mechanisms of phosphate solubilization by PSB are the production of organic acid generation and phosphatase enzyme activity (Li et al., 2022). Similarly, highly effective PSB isolates have been reported to markedly elevated soluble phosphorus concentration in culture media via acidification and enzymatic activity (Cheng et al., 2023). Highly active phosphate-solubilizing bacterial strains are essential for mobilizing inaccessible soil phosphorus and enhancing phosphorus-use efficiency in agricultural settings (Li et al., 2024; Chandrakala et al., 2019).

Table 1: Assessment of P solubilization efficiency of PSB in individual and in combined inoculation.


 
Dissolution potential of potash releasing bacteria
 
Important trait for potash releasing bacteria is EPS production, K release in Alexandrov’s broth assay.
 
ESP production and K dissolution
 
Raised colonies were found be positive in both the individual and in consortium showing the polysaccharide production. Available K was estimated by flame photometry at 15, 30 and 45th DAS. KRB culture produced 131.86 mg L-1 available K in individual inoculum and 111.7 mg L-1 available K in consortium (Table 2). The dissolution potential was found to be lower in consortium (81.13%) than the individual inoculum (92.27%). In an experiment incurred that Bacillus mucilaginosus increased the dissolution rate of silicate and aluminosilicate minerals and released the K+ and SiO2 by the production of organic acids like citric, fumaric glycolic, oxalic, tartaric acids etc. (Chen et al., 2015). Results obtained in this investigation are on in parallel with the previous studies with Rhizobium spp. (Sukumar et al., 2023); B. tequilensis SKSSB09 (Basak et al., 2023) and Bacillus mucilaginosus (Bhardwaj and Pal, 2023).

Table 2: Assessment of dissolution potential of KRB 9 potash releasing bacterial isolate.


 
Field studies
 
Significant difference in plant height was highest in plots applied with 100 per cent NPK and with seed treatment and soil application of consortium (T8) followed by 75 per cent NPK and with seed treatment and soil application of consortium. Plants applied with 100 per cent NPK and with seed treatment and soil application of consortium recorded highest values in all other biometric parameters like no. of branches (8.10 plant-1), nodule count (45.7 plant-1), biomass (129.0 g plant-1), pod count (242.5 plant-1), single plant yield (24.5 g) and grain yield (1237 kg ha-1). This was followed by 100 per cent NPK and with seed treatment and soil application of consortium which registered no. of branches (7.70 plant-1), nodule count (41.7 plant-1), biomass (137.7 g plant-1), pod count (232.0 plant-1) and grain yield (1227 kg ha-1). Grain yield was on par in T8 and T9. Recommended practice with 100 per cent NPK and seed treatment of Rhizobium and PSB recorded 163 pods per plant, 19.7 g grain yield plant-1 and 1012 kg ha grain yield. Lowest data were recorded in T1 (Table 3 and Fig 6).

Table 3: Effect of liquid bioinoculant consortium on yield and yield attributes of red gram during 2023-25.


        
Increased plant growth under consortium inoculation may be attributed to improved nitrogen fixation, phosphate solubilization, potassium mobilization and phytohormone production. Similar findings showed enhanced vegetative growth and nitrogen uptake in pulses due to increased rhizosphere activity (Singh et al., 2023), with comparable results in pigeon pea (Bargaz et al., 2018). Increased nodulation may result from native rhizobial activity, enhanced root growth and improved phosphorus and potassium availability, which promote nodule formation and biological nitrogen fixation. Similar benefits of microbial consortia on symbiotic nitrogen fixation have been reported (Muthusamy et al., 2023). Combined application of biofertilizers and inorganic fertilizers also improves plant growth, root development, nutrient uptake and nitrogen fixation (Chaudhary et al., 2022; Kumar et al., 2022; Rawat et al., 2021).
       
The T9 produced the best grain production with only 75 per cent of the prescribed NPK dose, suggesting the 75 per cent fertilizer dose is sufficient for good grain productivity (Fig 4, 5 and 6). Similar results have been reported, showing that the combined use of microbial consortia improved nutrient-use efficiency and sustained yields under reduced fertilizer application (Sharma et al., 2023;  Mishra et al., 2020). These results are in agreement with previous findings that considerable increases in pigeon pea production were achieved through combined inoculation with Rhizobium, PSB and KSB (Swaminathan et al., 2007). The nutrient uptake by red gram was significantly influenced by different treatments (Fig 7). The data revealed that integrated application of bioinoculants along with recommended fertilizer levels markedly enhanced nitrogen, phosphorus and potassium uptake compared to sole application of chemical fertilizers. The highest nitrogen (1.74 per cent); phosphorus (0.39%) and potassium (1.48%), uptake was recorded in 100 per cent recommended dose of NPK, seed treatment and soil application of consortium T8. comparatively lower N (1.45 per cent) and K (1.23%). was recorded in T1. The increase in nitrogen uptake under consortium treatments may be attributed to enhanced biological nitrogen fixation and improved root development, leading to better nutrient absorption (Prabhu et al., 2010; Singh et al., 2021). Biological nitrogen fixation by leguminous crops such as pigeon pea is a potential source of nitrogen input and a important for replenishing soil nitrogen (Namatsheve et al., 2025).

​

Fig 4: Illustrate the integrated response of red gram to liquid bioinoculant consortium.



​

Fig 5: Illustrate the pooled productivity and economic efficiency of red gram.



​

Fig 6: Illustrate the response of red gram to liquid bioinoculant consortium on yearwise.



​

Fig 7: Represent the plant nutrient uptake response of red gram to bioinoculant consortium.


       
The enhanced phosphorus uptake in consortium treatments may be due to the solubilization of insoluble phosphates by PSB and increased root proliferation, resulting in improved phosphorus acquisition. The improvement in potassium uptake could be attributed to the activity of KRB, which mobilized unavailable potassium into plant-available forms. Post-harvest soil analysis revealed significant improvement in soil fertility status under bioinoculant treatments (Fig 8 and 9). The available nitrogen (176 kg ha-1) phosphorus (52.2 kg ha-1) and K (178 kg ha-1) content was higher in soil which received 100 per cent NPK, seed treatment and soil application of consortium followed by 75 per cent recommended dose of NPK, seed treatment and soil application of consortium. The increase in soil nutrients under consortium treatments may be attributed to enhanced biological nitrogen fixation, P solubilization (Kushwaha and Mehta, 2023). and enzymatic activity and by K dissolution by the applied bioinoculants and they reduced nutrient losses. Our findings were supported by (Li et al., 2024; Chandrakala et al., 2019; Chen et al., 2015).

Fig 8: Represent the soil nutrients response of red gram to bioinoculant consortium.



Fig 9: Represent the seed nutrient quality response to bioinoculant treatments.


 
Economic analysis
BC ratio was worked out for all the treatments for the two years. Economic study showed large variations between treatments. The highest benefit-cost ratio was reported in T9 (2.86) followed by T8 and the lowest was recorded in T1 (2.04). Better yields was the main reason for the better profitability during consortium treatments. The higher profitability of T9 was primarily attributable to its greater grain yield, reduction in fertilizer cost, reduction in consortium cost and effective utilization of supplied fertilizers. This finding showed that consortium inoculation may be an economically effective and environmentally sustainable nutrient management approach for red gram agriculture. It was observed that with the help of biofertilizers applied both by seed treatment and soil application 75 per cent of NPK alone is sufficient for yield maximization. Similar results were also reported in previous studies (Sandeep et al., 2021; Krishnaprabu, 2020). 

CONCLUSION

The results of the present experiment clearly demonstrated that the integrated application of bioinoculants along with chemical fertilizers significantly enhanced the growth, yield, nutrient uptake, nodulation and soil fertility status of red gram. Compared with the 100 per cent recommended fertilizer dose combined with bioinoculant consortia, a 25 per cent reduction in the recommended chemical fertilizer dose could be achieved without adversely affecting crop productivity when supplemented with the bioinoculant consortium. Consortium-based treatments also considerably improved nodulation, the populations of beneficial soil microorganisms such as KRB and PSB and the uptake of major nutrients (N, P and K), along with improving the post-harvest soil nutrient status. These improvements in soil fertility parameters indicate the potential long-term benefits of integrated nutrient management for sustainable red gram production. Therefore, the application of 75 per cent of the recommended NPK dose in combination with the bioinoculant consortium is recommended as an effective strategy for enhancing nutrient use efficiency, reducing chemical fertilizer inputs and maintaining soil health.

ACKNOWLEDGEMENT

The present study was supported by Tamil Nadu Agricultural University, Coimbatore.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish or preparation of the manuscript.

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    Full Research Article

    Development and Evaluation of a Liquid Bio-inoculant Consortium for Enhancing Growth and Productivity of Redgram in the North-Eastern Zone of Tamil Nadu

    R
    R. Brindavathy1
    G
    G. Porkodi2,*
    M
    M. Gnanachithra3
    P
    P. Sivasakthivelan4
    B
    B. Karthikeyan5
    K
    K. Parameswari6,*
    R
    R. Abirami7
    1Department of Agricultural Microbiology, Oilseeds Research Station, Tindivanam-604 102, Tamil Nadu, India.
    2Department of Soil Science and Agricultural Chemistry, Agricultural College and Research Institute, Pudukkottai-622 104, Tamil Nadu, India.
    3Department of Agricultural Microbiology, TNAU, Coimbatore-641 003, Tamil Nadu, India.
    4Sugarcane Research Station, Cuddalore-607 001, Tamil Nadu, India.
    5Department of Agricultural Microbiology, Agricultural College and Research Institute Chettinad, Sivagangai-630 102, Tamil Nadu, India.
    6Department of Seed Science and Technology, Forest College and Research Institute, TNAU, Mettupalayam, Coimbatore-641 301, Tamil Nadu, India.
    7Department of Natural Resource Management, Horticulture College and Research Institute, Periyakulam, Theni-625 604, Tamil Nadu, India.

    • Submitted27-08-2026|

    • Accepted05-10-2026|

    • First Online 17-10-2026|

    • doi 10.18805/LR-5717

    ABSTRACT

    Background: Pigeonpea [Cajanus cajan (L.) Millsp.] is a protein-rich, drought tolerant pulse crop, cultivated in tropical and subtropical regions in India. Integrated crop management practices like balanced nutrients, bioinoculant and organic supplements would increase the redgram productivity. Liquid bioinoculants are preparations of living microorganisms in liquid formulation that increases soil vitality, fertility and productivity, as when applied to seeds, soil or plant surfaces. Multi-strain or microbial consortia with suitable combinations of beneficial microorganisms have evolved as cost effective components of sustainable agriculture. Hence research was planned to develop a consortium with redgram specific Rhizobium, Bacillus megaterium var. phosphaticum and Paenibacillus mucilaginosus (KRB-9).

    Methods: In vitro studies were carried out to evaluate the compatibility and shelf life of the consortium. Two-year field experiment was taken to study the effect of consortium on redgram with variety VBN 3. Bioinoculants were applied in form of seed treatment @ 125 ml ha-1 seeds and soil application @ 500 ml ha-1. Consortium and individual application was applied separately to evaluate their effects. The experiment comprised of nine treatments and 3 replications. The results of two years pooled values were revealed under investigation.

    Result: Among the treatments examined, highest plant height, biomass production, grain yield (1237 kg ha-1) and benefit-cost ratio (2.62) was observed when 75 per cent recommended fertilizer dose together with seed treatment and soil application of microbial consortium was used. This treatment was effective and inexpensive approach for sustainable red gram production.

    INTRODUCTION

    Redgram [Cajanus cajan (L.) Mill sp.] also known as pigeon pea is an important pulse crop cultivated in the tropical and subtropical regions of the world predominantly in India. It is an important source of dietary protein for a large section of vegetarian population. Additional to its high nutritional property, this legume plays a substantial role in soil fertility by biological nitrogen fixation (Kenzong et al., 2025) and most suited for sustainable agriculture (Fanish et al., 2023). Worldwide, India ranks first in red gram cultivable area and production and contributes major share in National pulse production and nutritional security (Hansen et al., 2020). Rhizobium have symbiotic association with redgram and endophytically occupies the nodules and fixes atmospheric nitrogen (Mula and Saxena, 2010). Moreover, the root architecture of this dicot, improves soil physical and chemical properties viz., soil structure, water infiltration, accumulation of soil organic matter (Ade et al., 2018).
           
    Though, redgram has ecological benefits, productivity is very low in India. One of the major constraints is the disproportionate and excessive use of chemical fertilizers, which deteriorates soil health, reduces nutrient use efficiency and increases production costs. While, continuous use of chemical fertilizers without organic or biological inputs leads to decrease in soil microbial activity and nutrient cycle mechanisms. Moreover, Tamil Nadu has the lowest area of 0.04 million ha with low production (0.05 million tonnes) and moderate productivity 1,039 kg/ha (Udgata et al., 2025) . The area and productivity has to be maximized to meet the redgram demand. Hence Bioinoculants and organic inputs are safe substitutes for chemical fertilizers. As a long duration pulse crop, bacterization with beneficial microorganism facilitates nutrient availability and increases the yield (Nosheen et al., 2021). Therefore, balanced nutrient management, involving judicious use of agrochemicals, increased use of organic amendments and integration of bioinoculants are necessary for enhancing soil fertility and crop yield in redgram cultivation.
           
    Bioinoculants are preparations of living microorganisms increases the rehabilitation and rejuvenation of soil vitality, as when applied colonize the rhizosphere or plant tissues and promotes the plant growth by increasing the nutrients availability through the mechanisms such as nitrogen fixation, nutrient solubilization, mobilization and recycling and helps in the maintenance of soil fertility and productivity (Riaz et al., 2020; Vessey, 2003; Pindi and Satyanarayana, 2012).  The utilization of bioinoculants has been employed for several decades and has been scientifically validated with crop-specific strains. Of late, multi-strain biofertilizers or microbial consortia with suitable combinations of beneficial microorganisms have evolved as important components of sustainable agriculture (Keshta, 2008). These microbial consortia help in plant growth, soil fertility enhancement and biological management of soil-borne diseases (Mousa et al., (2022).
           
    In India, liquid biofertilizers have emerged as a proven technology because of their unique production procedures and excellent properties. such as higher microbial population density, longer shelf life (more than one year), lower risk of contamination, ease of handling and transportation, lower production costs and compatibility with mechanized agriculture (Thompson, 1980) and hence gaining popularity. Studies on the application of liquid microbial consortia in redgram are limited. Hence a research was planned to develop a consortium, specifically for redgram to evaluate its effect on biometric parameters and yield attributes of red gram.

    MATERIALS AND METHODS

    In vitro studies
     
    Standard bioinoculants were utilized for the development of the consortium. Rhizobium (redgram specific CC1), Bacillus megaterium var phosphaticum (PS 2) and Paenibacillus mucilaginous (KRB-9) were cultivated in their respective nutritional broths. Rhizobium was cultivated in Yeast Extract Mannitol Broth -YEMA broth (Subba Rao, 1983) phosphobacteria in nutrient broth (Brindavathy and Shenbagavalli, 2021) and Paenibacillus mucilaginous in modified Alexandrov’s broth (Ben-David and Davidson, 2014). For consortium formulation the three-log phase bacterial cultures (23.2x109 CFU; 11.5x109 CFU and 17.3x109 CFU of Rhizobium, PSB and KRB respectively) were mixed in equal proportion and the individual cultures were preserved for comparative analysis. All the inoculated cultures were preserved for one year to examine their shelf life, population density and to evaluate the specific characteristics of each inoculum. Fifteen replications of each inoculum were maintained to draw samples.  Aliquots were periodically collected to enumerate the population by serial dilution and plating methods (CIMMYT, 1988). 
     
    Field experiments
     
    Geographical location of the experimental site
     
    The field experiments were conducted during the rabi seasons from 2023 to 2025 at the Oilseeds Research Station, Tindivanam, Tamil Nadu, situated at 12°21' N latitude, 79°66' E longitude and an altitude of 45.6 m above sea level. The soil type is sandy loam. The initial soil analysis at the experimental site were 21.6% coarse sand, 29.3% fine sand, 28.5% silt and 24.2% clay, medium organic carbon content (0.63%), low available nitrogen levels (242 kg ha-1), high available phosphorus concentrations (33.7 kg ha-1) and medium available potassium content (215 kg ha-1).
     
    Field layout and the application of inputs
     
    The field was thoroughly ploughed to fine tilth. The experiment composed with nine treatments with Randomized Block Design (RBD), each replicated three times. The red gram variety VBN 3 was sown with a row spacing of 45 x 90 cm. The biofertilizer strains Rhizobium (CC1), Phosphate Solubilizing Bacteria (PSB-1) and Potassium Releasing Bacteria (KRB-9) were used separately and in various consortium combinations according to the treatment schedule. The treatment structures were as follows: T1 - 100% NPK; T2 - 100% NPK with seed treatment of Rhizobium and PSB; T3 - 75% NPK with seed treatment of Rhizobium and PSB; T4 - 100% NPK with seed treatment of consortium; T5 - 75% NPK with seed treatment of consortium; T6 - 100% NPK with seed treatment and soil application of Rhizobium and PSB; T7 - 75% NPK with seed treatment and soil application of Rhizobium and PSB; T8 - 100% NPK with seed treatment and soil application of consortium; T9 - 75% NPK with seed treatment and soil application of consortium. The treatments were imposed by seed treatment with liquid biofertilizer inoculants at a rate of 125 mL ha-1 of seed quantity. The biofertilizer cultures were combined with farmyard manure (FYM) and applied at a rate of 500 mL ha-1 in accordance with the treatment plan.
     
    Data collection and sample processing
     
    Biometric observations namely plant height, number of branches, nodule number per plant and plant biomass were recorded at 45th DAS. Yield attributes viz., number of pods per plant and yield per ha were recorded. Soil samples were collected initially and at the time of harvest for soil nutrient analysis. Plant samples and seeds were collected to assess the nutrient content. The data collected were statistically analysed.
     
    Statistical analysis
     
    Analysis of variance (ANOVA) was performed using the SAS software, Bartlett’s Chi-square test, Aitken’s square root transformation, PROC GLM procedure were used for analysis. The graphs were developed using the STAR IRRI package (International Rice Research Institute, Philippines).
     
    Economics
     
    The experimental data for the two years were examined using standard methods formulated by CIMMYT to work out the economics (Bashan et al., 2023). The market prices of the inputs during 2025-2026 were used for calculating the budget.

    RESULT AND DISCUSSION

    In vitro studies: shelf-life studies and consortium compatibility
     
    Compatibility and shelf-life of rhizobium in individual and consortium formulations
     
    The population dynamics of Rhizobium in both individual and consortium formulations were observed at 30 days interval for up to 360 days after incubation (DAI) (Fig 1). A significant reduction in the cell population was noted during the storage duration in both formulations. The individual Rhizobium culture consistently exhibited a somewhat greater population than the consortium formulation.

    Fig 1: Shelf life of Rhizobium in individual and consortium inoculations during storage.


           
    The initial population of Rhizobium was 53.6 x 109  CFU ml-1 in the individual culture and 51.2 x 109  CFU ml-1 in the consortium. Following 30 days of storage, the population decreased slightly to 49.0 x 109  and 46.7 x 109  CFU ml-1, respectively. A gradual decline in cell viability was noted, recording 27.33 x 109 CFU ml-1 for the individual inoculum and 16.33 x 109 CFU ml-1 for the consortium at 300 DAI. At the end of the storage duration (360 DAI), the Rhizobium population exceeded 109 CFU ml-1 in both formulations, measuring 19.42 x 109 CFU ml-1 in the individual inoculum and 14.64 x 109 CFU ml-1 in the consortium.
           
    The minor decline in Rhizobium population under consortium circumstances may be ascribed to competition for resources and space among the microbial partners. Nonetheless, the preservation of viable populations exceeding the minimal suggested level after one year of storage unequivocally illustrates the compatibility of Rhizobium with phosphobacteria and potassium-releasing bacteria in the consortium formulation. Previous studies (Malusá and Vassilev, 2024).) reported analogous findings, indicating that multi-strain inoculants frequently display somewhat reduced individual populations owing to microbial interactions, although retain adequate viability for field application.
     
    Shelf-life of phosphobacteria in individual and consortium formulations
     
    The shelf life of phosphobacteria diminished progressively during the storage duration in both individual and consortium formulations (Fig 2). The individual phosphobacterial culture exhibited greater population than the consortium at all sampling intervals. The initial phosphobacterial population was 52.5 x 109 CFU ml-1 in the individual culture and 42.5 x 109 CFU ml-1 in the consortium. Subsequent declines were noted at 360 DAI, with populations attaining 20.54 x 109 CFU ml-1 in the individual culture and 12.72 x 109 CFU ml-1.

    Fig 2: Shelf life of phosphobacteria in individual and consortium inoculations during storage.


           
    Notwithstanding the decrease in viable counts, phosphobacteria sustained populations exceeding 109  CFU ml-1 for the whole storage duration. The shelf life of phosphobacteria exceeds more than a year demonstrates the suitability for liquid carrier medium and the compatibility among consortium members. Similar findings have been reported (Basak et al., 2021), noting the prolonged survival of phosphate-solubilizing bacteria in liquid biofertilizer formulations throughout extended storage durations.
     
    Shelf-life of potassium-releasing bacteria in individual and consortium formulations
     
    Similar results were found in KRB also (Fig 3). The initial population of KRB was 44.3 x 109  CFU ml-1 in the individual culture. Following 30 days of storage, the population stabilized at around 41.45 x 109 CFU ml-1 before experiencing a slow drop. At 300 DAI and 360 DAI, the population attained 20.86 x 109  and 18.82 x 109  CFU ml-1, respectively. The sustained presence of KRB populations above 109 CFU ml-1 after 360 days demonstrates exceptional shelf-life and formulation stability. The results align with previous findings that documented extended lifespan of potassium-solubilizing bacteria in liquid biofertilizer formulations under ambient storage conditions (O’Callaghan,  2023; Alori et al., 2017).

    Fig 3: Shelf life of potassium-releasing bacteria in individual and consortium inoculations during storage.


     
    Functional traits for liquid bioinoculants consortium and individual bioinoculants
     
    The phosphate-solubilizing capacity of phosphobacteria was assessed using plate assay and broth culture methods. Notable differences were noted between individual PSB inoculation and consortium inoculation regarding solubilization efficiency and inorganic phosphorus (Pi) emission. The individual PSB culture generated a greater solubilization zone diameter (1.6 cm) compared to the consortium (1.1 cm). Thus, the solubilization efficiency was significantly greater in the individual inoculation (207.69%) than in the consortium (120.00%). The development of an expanded halo zone surrounding the colony signifies increased secretion of organic acids and phosphatase enzymes that facilitate the dissolution of insoluble phosphate compounds in the medium. Similar findings was reported by Pan et al., (2021) registered that proficient phosphate-solubilizing bacterial strains demonstrated enhanced halo zone development attributed to heightened acidity of the surrounding medium and successful mineral phosphate solubilization.
           
    The solubilization of inorganic phosphorus in Pikovskaya’s broth augmented with the incubation duration in both treatments. The individual PSB culture exhibited Pi solubilization values of 35.20, 55.60 and 62.74 µg ml-1 at 7, 14 and 21 days after inoculation, respectively, yielding a mean value of 51.18 µg ml-1. The consortium inoculation recorded values of 38.40, 45.20 and 45.80 µg ml-1 at the respective intervals, with a mean of 43.13 µg ml-1 (Table 1). While the consortium demonstrated marginally elevated phosphorus solubilization at 7 days after inoculation (DAI), the individual PSB culture exceeded the consortium’s performance at 14 and 21 DAI, signifying its superior phosphate-solubilizing efficacy. The primary mechanisms of phosphate solubilization by PSB are the production of organic acid generation and phosphatase enzyme activity (Li et al., 2022). Similarly, highly effective PSB isolates have been reported to markedly elevated soluble phosphorus concentration in culture media via acidification and enzymatic activity (Cheng et al., 2023). Highly active phosphate-solubilizing bacterial strains are essential for mobilizing inaccessible soil phosphorus and enhancing phosphorus-use efficiency in agricultural settings (Li et al., 2024; Chandrakala et al., 2019).

    Table 1: Assessment of P solubilization efficiency of PSB in individual and in combined inoculation.


     
    Dissolution potential of potash releasing bacteria
     
    Important trait for potash releasing bacteria is EPS production, K release in Alexandrov’s broth assay.
     
    ESP production and K dissolution
     
    Raised colonies were found be positive in both the individual and in consortium showing the polysaccharide production. Available K was estimated by flame photometry at 15, 30 and 45th DAS. KRB culture produced 131.86 mg L-1 available K in individual inoculum and 111.7 mg L-1 available K in consortium (Table 2). The dissolution potential was found to be lower in consortium (81.13%) than the individual inoculum (92.27%). In an experiment incurred that Bacillus mucilaginosus increased the dissolution rate of silicate and aluminosilicate minerals and released the K+ and SiO2 by the production of organic acids like citric, fumaric glycolic, oxalic, tartaric acids etc. (Chen et al., 2015). Results obtained in this investigation are on in parallel with the previous studies with Rhizobium spp. (Sukumar et al., 2023); B. tequilensis SKSSB09 (Basak et al., 2023) and Bacillus mucilaginosus (Bhardwaj and Pal, 2023).

    Table 2: Assessment of dissolution potential of KRB 9 potash releasing bacterial isolate.


     
    Field studies
     
    Significant difference in plant height was highest in plots applied with 100 per cent NPK and with seed treatment and soil application of consortium (T8) followed by 75 per cent NPK and with seed treatment and soil application of consortium. Plants applied with 100 per cent NPK and with seed treatment and soil application of consortium recorded highest values in all other biometric parameters like no. of branches (8.10 plant-1), nodule count (45.7 plant-1), biomass (129.0 g plant-1), pod count (242.5 plant-1), single plant yield (24.5 g) and grain yield (1237 kg ha-1). This was followed by 100 per cent NPK and with seed treatment and soil application of consortium which registered no. of branches (7.70 plant-1), nodule count (41.7 plant-1), biomass (137.7 g plant-1), pod count (232.0 plant-1) and grain yield (1227 kg ha-1). Grain yield was on par in T8 and T9. Recommended practice with 100 per cent NPK and seed treatment of Rhizobium and PSB recorded 163 pods per plant, 19.7 g grain yield plant-1 and 1012 kg ha grain yield. Lowest data were recorded in T1 (Table 3 and Fig 6).

    Table 3: Effect of liquid bioinoculant consortium on yield and yield attributes of red gram during 2023-25.


            
    Increased plant growth under consortium inoculation may be attributed to improved nitrogen fixation, phosphate solubilization, potassium mobilization and phytohormone production. Similar findings showed enhanced vegetative growth and nitrogen uptake in pulses due to increased rhizosphere activity (Singh et al., 2023), with comparable results in pigeon pea (Bargaz et al., 2018). Increased nodulation may result from native rhizobial activity, enhanced root growth and improved phosphorus and potassium availability, which promote nodule formation and biological nitrogen fixation. Similar benefits of microbial consortia on symbiotic nitrogen fixation have been reported (Muthusamy et al., 2023). Combined application of biofertilizers and inorganic fertilizers also improves plant growth, root development, nutrient uptake and nitrogen fixation (Chaudhary et al., 2022; Kumar et al., 2022; Rawat et al., 2021).
           
    The T9 produced the best grain production with only 75 per cent of the prescribed NPK dose, suggesting the 75 per cent fertilizer dose is sufficient for good grain productivity (Fig 4, 5 and 6). Similar results have been reported, showing that the combined use of microbial consortia improved nutrient-use efficiency and sustained yields under reduced fertilizer application (Sharma et al., 2023;  Mishra et al., 2020). These results are in agreement with previous findings that considerable increases in pigeon pea production were achieved through combined inoculation with Rhizobium, PSB and KSB (Swaminathan et al., 2007). The nutrient uptake by red gram was significantly influenced by different treatments (Fig 7). The data revealed that integrated application of bioinoculants along with recommended fertilizer levels markedly enhanced nitrogen, phosphorus and potassium uptake compared to sole application of chemical fertilizers. The highest nitrogen (1.74 per cent); phosphorus (0.39%) and potassium (1.48%), uptake was recorded in 100 per cent recommended dose of NPK, seed treatment and soil application of consortium T8. comparatively lower N (1.45 per cent) and K (1.23%). was recorded in T1. The increase in nitrogen uptake under consortium treatments may be attributed to enhanced biological nitrogen fixation and improved root development, leading to better nutrient absorption (Prabhu et al., 2010; Singh et al., 2021). Biological nitrogen fixation by leguminous crops such as pigeon pea is a potential source of nitrogen input and a important for replenishing soil nitrogen (Namatsheve et al., 2025).

    ​

    Fig 4: Illustrate the integrated response of red gram to liquid bioinoculant consortium.



    ​

    Fig 5: Illustrate the pooled productivity and economic efficiency of red gram.



    ​

    Fig 6: Illustrate the response of red gram to liquid bioinoculant consortium on yearwise.



    ​

    Fig 7: Represent the plant nutrient uptake response of red gram to bioinoculant consortium.


           
    The enhanced phosphorus uptake in consortium treatments may be due to the solubilization of insoluble phosphates by PSB and increased root proliferation, resulting in improved phosphorus acquisition. The improvement in potassium uptake could be attributed to the activity of KRB, which mobilized unavailable potassium into plant-available forms. Post-harvest soil analysis revealed significant improvement in soil fertility status under bioinoculant treatments (Fig 8 and 9). The available nitrogen (176 kg ha-1) phosphorus (52.2 kg ha-1) and K (178 kg ha-1) content was higher in soil which received 100 per cent NPK, seed treatment and soil application of consortium followed by 75 per cent recommended dose of NPK, seed treatment and soil application of consortium. The increase in soil nutrients under consortium treatments may be attributed to enhanced biological nitrogen fixation, P solubilization (Kushwaha and Mehta, 2023). and enzymatic activity and by K dissolution by the applied bioinoculants and they reduced nutrient losses. Our findings were supported by (Li et al., 2024; Chandrakala et al., 2019; Chen et al., 2015).

    Fig 8: Represent the soil nutrients response of red gram to bioinoculant consortium.



    Fig 9: Represent the seed nutrient quality response to bioinoculant treatments.


     
    Economic analysis
    BC ratio was worked out for all the treatments for the two years. Economic study showed large variations between treatments. The highest benefit-cost ratio was reported in T9 (2.86) followed by T8 and the lowest was recorded in T1 (2.04). Better yields was the main reason for the better profitability during consortium treatments. The higher profitability of T9 was primarily attributable to its greater grain yield, reduction in fertilizer cost, reduction in consortium cost and effective utilization of supplied fertilizers. This finding showed that consortium inoculation may be an economically effective and environmentally sustainable nutrient management approach for red gram agriculture. It was observed that with the help of biofertilizers applied both by seed treatment and soil application 75 per cent of NPK alone is sufficient for yield maximization. Similar results were also reported in previous studies (Sandeep et al., 2021; Krishnaprabu, 2020). 

    CONCLUSION

    The results of the present experiment clearly demonstrated that the integrated application of bioinoculants along with chemical fertilizers significantly enhanced the growth, yield, nutrient uptake, nodulation and soil fertility status of red gram. Compared with the 100 per cent recommended fertilizer dose combined with bioinoculant consortia, a 25 per cent reduction in the recommended chemical fertilizer dose could be achieved without adversely affecting crop productivity when supplemented with the bioinoculant consortium. Consortium-based treatments also considerably improved nodulation, the populations of beneficial soil microorganisms such as KRB and PSB and the uptake of major nutrients (N, P and K), along with improving the post-harvest soil nutrient status. These improvements in soil fertility parameters indicate the potential long-term benefits of integrated nutrient management for sustainable red gram production. Therefore, the application of 75 per cent of the recommended NPK dose in combination with the bioinoculant consortium is recommended as an effective strategy for enhancing nutrient use efficiency, reducing chemical fertilizer inputs and maintaining soil health.

    ACKNOWLEDGEMENT

    The present study was supported by Tamil Nadu Agricultural University, Coimbatore.

    CONFLICT OF INTEREST

    The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish or preparation of the manuscript.

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