Discover how phosphate-solubilizing bacteria (PSB) biofertilizers enhance maize biomass production and improve soil microbial carbon for sustainable agriculture.
Imagine a bustling underground city teeming with microscopic workers that tirelessly mine nutrients for crops, asking nothing in return. This isn't science fiction—it's the reality happening in healthy agricultural soils, where phosphate-solubilizing bacteria (PSB) serve as invisible allies in our quest for sustainable food production.
of soil phosphorus remains locked away in forms plants can't absorb 5
of all culturable soil bacteria are phosphate-solubilizing 5
Phosphorus is an essential macronutrient required for critical processes in plants, from energy production and photosynthesis to cell division and membrane integrity. Ironically, although most agricultural soils contain substantial amounts of phosphorus, up to 99.9% remains locked away in forms that plants cannot directly absorb 5 .
This phosphorus paradox has forced farmers to apply large quantities of chemical fertilizers, creating a costly dependency that carries significant environmental concerns, including water pollution from phosphorus runoff.
Enter phosphate-solubilizing bacteria—nature's key to unlocking this phosphorus prison. These remarkable microorganisms have evolved sophisticated mechanisms to liberate bound phosphorus and make it available to plants. The implications for maize cultivation are particularly exciting, as research demonstrates that these microscopic allies not only boost crop productivity but also build healthier, more resilient soil ecosystems 4 5 .
Phosphate-solubilizing bacteria function as nature's sophisticated mining crew, capable of transforming insoluble phosphorus into forms that plants can readily absorb. These microorganisms belong to various genera including Bacillus, Pseudomonas, Pantoea, and Burkholderia, among others 5 .
They account for 1-50% of the total phosphate-solubilizing microorganisms in soil and represent approximately 40% of all culturable soil bacteria 5 , highlighting their ecological significance.
PSB release organic acids like gluconic acid that chelate binding cations or lower pH to dissolve phosphate compounds.
They produce extracellular enzymes called phosphatases that mineralize organic phosphorus forms.
Some PSB strains produce growth-promoting substances like auxins, gibberellins, and cytokinins 4 .
Beyond their phosphorus-solubilizing capabilities, these bacteria contribute to broader soil health through multiple pathways. As they colonize the rhizosphere—the soil region directly influenced by plant roots—they create a thriving microbial ecosystem that enhances plant growth through various direct and indirect mechanisms.
Perhaps most importantly, PSB inoculation increases soil microbial biomass carbon, a key indicator of soil health and fertility. This microbial biomass acts as a nutrient reservoir, slowly releasing nutrients back into the soil when microbial cells die and decompose. Studies have shown that soils treated with PSB biofertilizers maintain higher microbial biomass carbon throughout the crop growth cycle, with particularly pronounced effects during the flowering stage 4 . This vibrant microbial community represents a living bridge between soil minerals and plant health, facilitating a more efficient nutrient cycling system that supports sustainable agriculture.
To understand how PSB biofertilizers perform under real-world conditions, a comprehensive field study was conducted in Puranchaur, Kaski, Nepal, during the 2023 growing season 1 8 .
The experiment employed a randomized complete block design (RCBD) with seven treatments and three replications each, a robust statistical approach that helps account for field variability. The maize variety tested was Arun-2, a popular choice in the region.
The findings from the Nepal experiment demonstrated compelling advantages for the integrated approach. The treatment combining the recommended NPK dose with PSB inoculation emerged as the clear winner, producing the highest maize yield of 3.92 Mt·ha⁻¹ 1 8 . This significantly outperformed the control treatment, which yielded only 3.05 Mt·ha⁻¹, and showed a noticeable improvement over chemical fertilizers applied alone.
| Treatment | Description | Yield (Mt·ha⁻¹) |
|---|---|---|
| T1 | Control (no fertilizers) | 3.05 |
| T2 | Recommended NPK dose | [Not specified in search results] |
| T3 | Recommended NPK dose + PSB | 3.92 |
| ... | Other combinations | Ranging between 3.05-3.92 |
Beyond the raw yield numbers, the researchers observed that the PSB-enhanced treatment positively influenced all measured growth and yield parameters 1 . The plants developed more robust vegetative growth, stronger stalks, and more filled grains per cob—all indicators of healthier plants operating at their genetic potential.
While the visible effects on maize growth are impressive, the revolution triggered by PSB inoculation extends deep into the soil ecosystem. Soil microbial biomass carbon represents the living component of soil organic matter—a dynamic reservoir of nutrients and a key indicator of soil health.
Think of it as a measure of the "microbial workforce" available in the soil to perform essential ecosystem services like nutrient cycling, organic matter decomposition, and soil structure formation 7 9 .
Research shows that microbial biomass responds more rapidly to changes in soil management than general soil organic carbon, making it an early warning system for soil degradation or an early indicator of recovery 7 9 .
The introduction of phosphate-solubilizing bacteria creates ripple effects throughout the soil microbial community. A 2017 study conducted in Telangana, India, meticulously tracked changes in soil microbial biomass carbon at different growth stages of maize—vegetative, flowering, and harvest 4 .
| Growth Stage | Soil Microbial Biomass Carbon (µg kg⁻¹) |
|---|---|
| Vegetative | 102.06 |
| Flowering | 140.33 |
| Harvest | 121.73 |
This pattern suggests that PSB inoculation doesn't just add a single functional group of bacteria; it stimulates the entire soil food web. The enhanced microbial activity creates a more biologically active soil environment where nutrients are continuously recycled and made available to plants.
Recent research has revealed that the effectiveness of PSB is influenced by complex interactions between carbon (C) and phosphorus (P) availability in soils. A sophisticated 2025 pot experiment examined these relationships using a 2×3×2 complete factorial design that tested two P levels, three C levels, and two PSB levels 5 6 .
The study demonstrated that PSB addition alone caused an average increase of 3.03% in maize shoot biomass. However, the combination of PSB with exogenous phosphorus (50 mg kg⁻¹) significantly enhanced nitrogen concentration, nitrogen uptake, and phosphorus uptake in maize plants 5 6 .
For farmers and agricultural practitioners interested in harnessing these benefits, modern PSB products are increasingly accessible and user-friendly. These biofertilizers are typically available in liquid or powder formulations with concentrations of viable bacteria around 1×10⁹ CFU mL⁻¹ for liquid products 5 .
| Material/Reagent | Function in PSB Research & Application |
|---|---|
| PSB Inoculant | Contains live phosphate-solubilizing bacteria (e.g., Pantoea septica) |
| Carrier Materials (talc, charcoal, etc.) | Medium for distributing and protecting bacteria in solid formulations |
| Liquid Culture Medium | Growth medium for bacterial multiplication before application |
| 0.5 M K₂SO₄ Solution | Standard extractant for measuring microbial biomass carbon |
| Glucose (Carbon Source) | Used in studies to examine C-P-SB interactions in soil |
| Potassium Dihydrogen Phosphate | Standard phosphorus source for experimentation |
| Chloroform (CHCl₃) | Used in fumigation-extraction method for microbial biomass measurement |
Match the right bacterial strains to local soil conditions and crop needs. Different PSB strains have varying capabilities for solubilizing different types of insoluble phosphates.
Protect products from extreme temperatures and use them before expiration to ensure maximum viability of the microorganisms when applied .
Use seed treatment, soil application, or seedling root dip to establish beneficial bacteria in the rhizosphere where they can interact with plant roots.
Combine PSB with appropriate levels of chemical fertilizers to optimize nutrient availability and maximize crop productivity.
The research evidence makes a compelling case for integrating phosphate-solubilizing bacteria into mainstream agricultural practice. When deployed effectively, PSB technology offers a triple win: for farmers through improved yields and reduced fertilizer costs, for the environment through decreased chemical runoff and more efficient nutrient use, and for soil health through enhanced microbial diversity and activity.
The combined application of chemical fertilizers with PSB represents a pragmatic middle path—a way to optimize rather than eliminate synthetic inputs while building biological soil fertility. This approach aligns with the principles of sustainable intensification, seeking to maximize productivity per unit of land while minimizing environmental impacts 1 .
While our understanding of PSB has advanced significantly, important research questions remain. Scientists continue to explore how to match specific PSB strains to different soil types, climate conditions, and crop varieties. The development of more stable formulations with longer shelf lives and better field performance represents another active area of innovation.
The story of phosphate-solubilizing bacteria and maize cultivation illustrates a broader principle: that some of the most powerful solutions in agriculture come not from dominating natural systems, but from understanding and collaborating with them. These microscopic allies have been present in soils all along, waiting for us to recognize their potential and incorporate them into our farming practices.
As research continues to reveal the sophisticated relationships between plants and their microbial partners, we gain new opportunities to build agricultural systems that are both productive and regenerative. The integration of PSB biofertilizers into maize cultivation represents more than just a technical innovation—it's a step toward a more holistic, ecological approach to farming that honors the biological complexity of healthy soils.
By embracing these tiny underground helpers, we take an important stride toward a future where we can meet our food production needs while nurturing the living earth that sustains us all.