Scientists tested whether adding helpful bacteria to soybean seeds could make plants grow better and produce more soybeans. They ran five different experiments over two years, trying various combinations of bacteria that help plants absorb nutrients from soil. The best results came from using two specific bacteria together: one that helps roots grab nitrogen from the air, and another that boosts overall plant growth. These bacteria combinations increased soybean yields and helped plants develop stronger root systems, suggesting farmers might need less chemical fertilizer in the future.

The Quick Take

  • What they studied: Whether coating soybean seeds with special growth-promoting bacteria could help plants produce more soybeans and reduce the need for chemical fertilizers
  • Who participated: Five separate experiments conducted over two growing seasons (2020-2022) in Brazil, testing different combinations of bacteria on soybean plants
  • Key finding: Two specific bacteria combinations worked best: Bradyrhizobium japonicum paired with either Pseudomonas fluorescens or Bacillus aryabhattai. These combinations increased the number of root nodules (where nitrogen is captured), improved root growth, and boosted soybean yields across different growing conditions
  • What it means for you: Farmers may be able to reduce chemical fertilizer use while maintaining or improving crop yields by using these beneficial bacteria. This could lower farming costs and reduce environmental impact, though more real-world testing on different farms is still needed

The Research Details

Researchers conducted five separate experiments over two growing seasons in Brazil. In the first two experiments, they compared eight different treatments: no bacteria (control), one type of bacteria alone, and various combinations of up to six different bacteria species. The bacteria were applied by coating the soybean seeds before planting. The third and fourth experiments tested whether irrigation (water supply) affected how well the bacteria worked. The fifth experiment tested whether the bacteria could replace some of the chemical fertilizer normally used on soybeans. Each experiment used a randomized block design, meaning treatments were randomly assigned to different plots to ensure fair comparisons.

This research approach is important because it tests bacteria combinations under real farming conditions rather than just in laboratory settings. By running multiple experiments across different seasons and conditions, the scientists could confirm that the results weren’t just luck or due to one specific year’s weather. Testing with different irrigation and fertilizer levels shows whether these bacteria work in various farming situations

The study used proper scientific methods with control groups, multiple replications (repeating each treatment four times), and randomized assignments to reduce bias. Testing across two growing seasons strengthens confidence in the results. However, the study doesn’t specify exact sample sizes for all experiments, and results were specific to Brazilian growing conditions, so results may differ in other regions

What the Results Show

The best results came from two specific bacteria combinations. When Bradyrhizobium japonicum (a bacteria that helps plants capture nitrogen from air) was paired with either Pseudomonas fluorescens or Bacillus aryabhattai, soybean plants showed significant improvements. These combinations increased the number of nodules on roots (the structures where nitrogen is captured) and increased the total mass of these nodules, meaning more nitrogen was being captured from the air. Root systems grew larger and more extensive, with greater surface area and volume. Most importantly, these combinations increased the total soybean grain yield—the actual amount of soybeans harvested—across multiple growing locations and conditions.

The study also measured the weight of 1,000 individual soybean grains and found improvements with the best bacteria combinations. Soil coverage rates (how much of the soil surface was covered by plant growth) also improved. When the researchers tested whether these bacteria could reduce the need for chemical fertilizer, they found promising results suggesting that farmers might be able to use less fertilizer while maintaining good yields, particularly because the bacteria improved root volume and nutrient absorption capacity

This research builds on previous studies showing that individual growth-promoting bacteria can help crops. The key new finding is that combining two specific bacteria together (called coinoculation) works better than using them separately. This synergistic effect—where two things work better together than apart—is an important discovery that hadn’t been fully demonstrated before in soybean production

The study was conducted only in Brazil, so results may not apply equally to other regions with different climates or soil types. The exact number of plants tested in each experiment wasn’t clearly specified. The research was conducted on research stations rather than on commercial farms, so real-world results on actual farms might differ. The study didn’t test these bacteria combinations over more than two growing seasons, so long-term effects remain unknown. Additionally, the economic cost of the bacteria treatments compared to traditional fertilizer wasn’t analyzed

The Bottom Line

Based on this research, farmers may consider using Bradyrhizobium japonicum combined with either Pseudomonas fluorescens or Bacillus aryabhattai as a seed treatment. This appears to increase yields and may allow for some reduction in chemical fertilizer use. However, confidence level is moderate—more testing on commercial farms in different regions is recommended before making major changes to fertilizer practices. Farmers should start with small test areas before applying to entire fields

Soybean farmers in tropical and subtropical regions similar to Brazil should find this most relevant. Farmers interested in sustainable or organic practices would particularly benefit. This may be less immediately applicable to farmers in very different climates until additional research is conducted. Agricultural scientists and extension agents advising farmers should also pay attention to these findings

Improvements in plant growth and root development would likely be visible within 4-6 weeks of planting. Yield increases would be measurable at harvest time (approximately 4-5 months after planting). To see the full benefits of reduced fertilizer needs, farmers would likely need to test this approach for at least one full growing season

Want to Apply This Research?

  • Track soybean yield per acre and fertilizer application rates across growing seasons. Measure these metrics: total grain yield (bushels or kg per hectare), amount of chemical fertilizer applied (kg per hectare), and estimated cost per unit of production. Compare years when bacteria treatments are used versus years with standard fertilizer practices
  • Start by treating seeds with the recommended bacteria combination (Bradyrhizobium japonicum + Pseudomonas fluorescens or Bacillus aryabhattai) on a small test plot (1-2 acres). Reduce chemical fertilizer by 25-50% on the test plot while maintaining normal fertilizer on control plots. Document observations about plant growth, root development, and final yield
  • Use the app to log weekly observations: plant height, visible plant health, soil moisture levels, and any pest or disease issues. At harvest, record exact yield measurements and fertilizer costs. Compare test plots to control plots over multiple seasons to determine if bacteria treatments provide consistent benefits in your specific growing conditions

This research presents promising laboratory and research station findings about using beneficial bacteria to improve soybean production. However, results were obtained in Brazil and may not apply equally to all regions or farming conditions. Before making significant changes to fertilizer practices or seed treatments, farmers should consult with local agricultural extension services or agronomists familiar with their specific growing conditions. Individual results may vary based on soil type, climate, irrigation availability, and other local factors. This information is for educational purposes and should not replace professional agricultural advice. Always follow label instructions for any commercial bacterial inoculant products used