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Synergism between phosphate fertilization and phosphate-solubilizing microorganisms enhances phosphorus use efficiency in a soybean–maize succession

This study demonstrates that inoculating soybean–maize succession systems in tropical Cerrado Oxisols with phosphate-solubilizing microorganisms (*Bacillus subtilis* and *Priestia megaterium*) synergistically enhances soil phosphorus availability, plant nutrition, and crop yield when combined with monoammonium phosphate fertilization, thereby improving overall phosphorus use efficiency.

Original authors: Thays Mendonça Oliveira, Veridiana Cardozo Gonçalves Cantão, Jessyca Adriana Gomes Florêncio Silva, Ricardo Castro Dias, Juliana Silva Rodrigues Cabral, Wanessa Thais Ferreira Duarte, Sudip Sarkar, An

Published 2026-07-09

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CC BY 4.0

Original authors: Thays Mendonça Oliveira, Veridiana Cardozo Gonçalves Cantão, Jessyca Adriana Gomes Florêncio Silva, Ricardo Castro Dias, Juliana Silva Rodrigues Cabral, Wanessa Thais Ferreira Duarte, Sudip Sarkar, Antônio Jussiê Silva Solino

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: Unlocking a Locked Treasure Chest

Imagine a farmer's soil is like a giant treasure chest filled with gold (Phosphorus), which is essential for plants to grow big and strong. However, in tropical soils (like the Cerrado in Brazil), this gold is locked inside a very tough, rusty box. The plants can't reach it on their own.

Traditionally, farmers try to break the box open by throwing in huge amounts of chemical fertilizer (the "key"). But this is expensive, and often, the soil just locks the new gold away again, wasting money and polluting the environment.

This study asked a simple question: What if we hire a team of tiny, specialized locksmiths (microorganisms) to help us open the box, so we don't need to throw in as many chemical keys?

The Experiment: The "Locksmiths" and the "Keys"

The researchers set up a field experiment with two popular crops: Soybeans (a legume) and Maize (corn). They tested different combinations of:

Chemical Keys: Different amounts of phosphate fertilizer (Monoammonium Phosphate).
Tiny Locksmiths: Two specific types of bacteria (Bacillus subtilis and Priestia megaterium) known for their ability to dissolve locked-up phosphorus.
The Control: A group with no fertilizer and no bacteria (the "do nothing" group).

They wanted to see if the bacteria could help the plants get more nutrients, grow better, and produce more food, especially when using less fertilizer.

What Happened to the Soybeans? (The "Steady Eddy")

Think of the soybean crop as a very efficient, cautious driver.

The Result: Even without adding extra chemical fertilizer, the soybeans did just fine when the "tiny locksmiths" were present. In fact, the bacteria helped the plants grab more of the natural gold already sitting in the soil.
The Yield: The amount of soybeans harvested didn't change much whether they used bacteria, fertilizer, or both. Why? Because the soil already had enough gold to feed the plants; the plants weren't "hungry" enough to need more.
The Takeaway: The bacteria acted like a helpful assistant, making sure the plants got exactly what they needed from the soil without needing a massive chemical boost.

What Happened to the Maize? (The "Growth Spurt")

Now, imagine the maize crop as a teenager going through a growth spurt. It needs a lot of energy and nutrients to get tall and produce heavy ears of corn.

The Result: The maize loved the combination of the "tiny locksmiths" and the chemical fertilizer. As the researchers added more fertilizer, the maize yield went up in a straight, predictable line.
The Synergy: The bacteria didn't just help a little; they made the fertilizer work much better. It's like giving the teenager a high-quality meal (fertilizer) and a personal trainer (bacteria) to help them absorb the nutrients. The result was significantly more corn.

What About the Soil's Health?

The researchers also looked under the hood of the soil to see how the "engine" was running.

The Good News: The bacteria made the soil more active. Specifically, they increased the activity of an enzyme called β-glucosidase. Think of this enzyme as the soil's "digestive system." When it's active, it means the soil microbes are happily eating and recycling organic matter, keeping the soil healthy and alive.
The Neutral News: Some other soil enzymes (the "specialized tools" for breaking down specific minerals) didn't change much. This is actually normal; when there is plenty of food (phosphorus) available, the soil microbes don't need to work as hard to find it, so they stop producing those specific tools.

The Bottom Line

This study shows that using these specific "tiny locksmiths" (bacteria) alongside fertilizer is a winning strategy, but it works differently for different crops:

For Soybeans, the bacteria helped the plants access natural soil nutrients efficiently, keeping them healthy without needing extra chemicals.
For Maize, the bacteria acted as a force multiplier, helping the plants turn fertilizer into a much bigger harvest.

In short: By teaming up nature's tiny workers with traditional fertilizer, farmers can get better results from their crops and use their resources more wisely, especially in tough tropical soils.

Technical Summary: Synergism between Phosphate Fertilization and Phosphate-Solubilizing Microorganisms in a Soybean–Maize Succession

Problem Statement
Phosphorus (P) is a critical macronutrient for crop growth, yet its efficiency in tropical soils, particularly highly weathered Oxisols of the Cerrado biome, remains low due to strong fixation by iron and aluminum oxides. This limitation necessitates high rates of phosphate fertilization, which increases production costs and poses environmental risks such as eutrophication. While phosphate-solubilizing microorganisms (PSMs) offer a biological mechanism to mobilize insoluble P, there is a lack of field data regarding their synergistic effects with mineral fertilizers in integrated soybean–maize succession systems. This study addresses the knowledge gap concerning how combined PSM inoculation and varying rates of monoammonium phosphate (MAP) affect soil P availability, biochemical activity, plant physiology, and yield in tropical conditions.

Methodology
The research was conducted as a field experiment in Montividiu, Goiás, Brazil, during the 2023/2024 growing season on a Cerrado Oxisol with an initial available P level of 25 mg dm⁻³. The study employed a randomized complete block design (RCBD) with four replications. Treatments consisted of five P₂O₅ rates (0, 19.5, 39.0, 58.5, and 78.0 kg ha⁻¹) applied as MAP, combined with or without inoculation of two specific PSM strains: Bacillus subtilis (CNPMS B2084) and Priestia megaterium (CNPMS B119). An absolute control (no P, no PSM) was included.

The experiment evaluated a soybean–maize succession. Soybean (Glycine max, cv. Soy Combate IPRO) was sown in October 2023, followed by maize (Zea mays, hybrid MG597) in March 2024. Key measurements included:

Agronomic Traits: Pod number, grains per pod, grain yield, and thousand-grain weight.
Nutritional Status: Leaf and grain P concentrations.
Physiological Parameters: Chlorophyll a fluorescence transients (O–J–I–P protocol) to assess Photosystem II (PSII) performance, including reaction center closure rates, quantum yields, and electron transport probabilities.
Soil Biochemical Attributes: Available soil P (Mehlich-1), enzymatic activities ( $\beta$ -glucosidase, arylsulfatase, acid and alkaline phosphatases), and easily extractable glomalin-related soil protein (EE-GRSP).

Data were analyzed using ANOVA and polynomial regression models, with comparisons made against the absolute control using least significant difference (LSD) tests.

Key Results
The study revealed distinct responses between the two crops and specific biochemical changes:

Soybean Response: Inoculation with PSM increased soil P availability and leaf P concentration compared to the control, even without mineral P addition. However, grain yield was not significantly affected by the treatments, averaging 4,199 kg ha⁻¹ across P + PSM treatments. The number of pods per plant in treatments receiving $\ge$ 19.5 kg ha⁻¹ of P₂O₅ was actually lower than the absolute control. Leaf P concentration decreased quadratically with increasing P rates, while grain P concentration increased linearly. PSII photochemical parameters remained stable across all treatments.
Maize Response: Maize exhibited a stronger response to the combined treatments. Grain yield increased linearly with P₂O₅ rates under PSM inoculation, with doses $\ge$ 26 kg ha⁻¹ resulting in yields exceeding 3.5 Mg ha⁻¹ compared to 3.2 Mg ha⁻¹ in the control. Leaf P concentration showed a quadratic response, peaking at 41.5 kg ha⁻¹ of P₂O₅.
Soil Biochemistry: $\beta$ -glucosidase activity increased linearly with P₂O₅ + PSM application in both crops, indicating enhanced microbial carbon cycling. Conversely, arylsulfatase activity remained stable. Acid and alkaline phosphatase activities were generally unaffected or decreased in the presence of P + PSM, suggesting a downregulation of enzyme synthesis when inorganic P is available. Glomalin content remained stable across treatments.

Key Contributions and Significance
The paper demonstrates that the synergistic application of Bacillus subtilis and Priestia megaterium with mineral phosphate fertilizers enhances phosphorus use efficiency in tropical soybean–maize systems, though the magnitude of the benefit is crop-dependent.

Crop-Specific Dynamics: The study highlights that C₄ crops (maize) show a linear yield response to the combined treatment, likely due to higher photosynthetic capacity and nutrient demand, whereas C₃ crops (soybean) maintained stable yields but showed improved nutrient uptake efficiency without yield penalties.
Mechanism of Action: The results confirm that PSM inoculation effectively mobilizes native or fixed soil P, as evidenced by increased leaf P in soybean without mineral fertilizer. The linear increase in $\beta$ -glucosidase activity suggests that the combined treatment stimulates broader microbial metabolism and organic matter turnover.
Physiological Stability: The stability of PSII photochemical parameters across all treatments indicates that the applied P rates and PSM inoculation did not induce photosynthetic stress, maintaining plant physiological health.
Sustainable Management: The authors conclude that PSM inoculation is an effective strategy to improve P use efficiency. The findings suggest that these microorganisms can complement mineral fertilization, potentially allowing for reduced reliance on high P doses in tropical cropping systems without compromising agronomic performance, thereby contributing to more sustainable nutrient management.

The paper modestly frames these findings as an advancement in understanding biotic-abiotic interactions under field conditions, noting that long-term assessments and cost-benefit analyses are necessary for large-scale adoption.