Overview
The NC State Soil Microbiome Extension program conducted small plot field trials in 2025 evaluating microbial biostimulant seed treatments for soybean. Microbial biostimulants are beneficial organisms (bacteria and fungi) that may increase crop yield by increasing plant nutrient access and nutrient use efficiency or enhancing plant stress tolerance. While microbial seed treatments are promising solutions for reducing synthetic inputs and/or boosting yield, product field performance can be highly variable. The objective of this multi-year study (2024, 2025, and 2026) is to evaluate field efficacy of microbial seed treatments on soybean production across North Carolina’s regional environments.
Study Design
Trials were installed at 6 Official Variety Testing (OVT) county locations spanning three North Carolina ecoregions (Figure 1) including Beaufort and Pasquotank (Tidewater), Robeson and Sampson (Coastal Plain), and Rowan and Union (Piedmont). See Supporting Information for soil characteristics, site details, and 2025 weather data.
Figure 1. U.S. Geological Survey and Environmental Protection Agency (EPA) map of North Carolina ecoregions. Stars indicate OVT field trial locations for this study.
Asgrow Bayer Crop Sciences soybean seeds MG 5.7 (AG57XF1 pre-treated with Acceleron fungicide and insecticide) were treated in house with 2 commercially available microbial biostimulants according to the manufacturer’s application rates (see Table 1). BioWake is a single bacterium and Buncha Bugs is a combination of bacterial strains and fungi; both product formulations are beneficial microbes that may improve seedling vigor and enhance nutrient access and uptake.
Microbial seed treatments and a non-treated (no microbe control) were installed at each location using a randomized block design (4 x 20 ft rows with 15” row spaces) with 16 replicates per treatment. Full season crop was planted within 1-6 days of treatment in late May-early June 2025.
| Product | Company | Guaranteed Analysis | Formulation | Application Rate |
| BioWake | AMVAC GreenSolutions | Methylobacterium hispanicum 1 x 109 cfu/g | Biological seed lubricant; Flowable powder | 1 oz/100 lbs seed |
| Buncha Bugs DF ST | Concept AgriTek LLC | Bacillus mucilaginosus 4.23 x 108 cfu/g, Bacillus subtilis 2.6 x 108 cfu/g, Bacillus megaterium 1.3 x 108 cfu/g, Bacillus licheniform 1.3 x 108 cfu/g, Bacillus simplex 1.3 x 108 cfu/g, Mycorrhizal fungi 368 ppg/g | Powder | 0.53 oz/100 lbs seed |
Results
Across the study, soybean yield did not differ between microbial seed treatments and non-treated (no microbe) controls (Figure 2). Yield differed significantly between locations (Table 2), and relative differences were consistent with 2025 Soybean OVT data. Within location, we generally did not observe yield differences between seed treatments (Figure 3). Two exceptions include Robeson (i.e., greater yield in Buncha Bugs compared to Non-Treated) and Rowan (i.e., greater yield in Buncha Bugs compared to BioWake). Importantly, these observations lack the statistical support to make broader claims that treatments drive yield differences across locations.
Figure 2. Soybean yield (bu/acre) for each microbial treatment and non-treated control (see Legend) calculated across the trial’s 6 locations. Box plots show the yield distribution, and the median value is indicated by the black line. Average yield is also reported for each treatment.
Figure 3. Soybean yield (bu/acre) for each microbial treatment and non-treated control (see Legend) at each trial location. Red brackets show where we observed significant yield differences (P-value < 0.05) between treatments at a single location.
| Location | Average Yield (bu/acre) | Significance Group |
| Beaufort | 56.7 | c |
| Pasquotank | 80.0 | a |
| Robeson | 69.4 | b |
| Rowan | 71.5 | ab |
| Sampson | 59.8 | bc |
| Union | 49.9 | c |
Finally, since biostimulants may increase plant nutrient uptake, we measured leaf nutrient content at mid-late vegetative stage (V4-V6). We were unable to collect samples from Rowan due to logistical reasons. Phosphorus and potassium, but not nitrogen, differed between locations but not by microbial treatment (Figure 4). Note that all plant nutrient levels were within normal ranges with no deficiencies or excess.
Figure 4. Bars graphs show mid-late vegetative stage soybean leaf nutrient content (%) for nitrogen (top) phosphorus (middle), and potassium (bottom). Bar colors indicate microbial seed treatment or non-treated (see Legend).
Summary
- Soybean yield varied between locations, and yield patterns are consistent with 2025 Soybean OVT site comparisons.
- Microbial biostimulant seed treatments had no significant impact on yield. Yield differences between treated and non-treated controls were negligible (Figure 5).
- Environmental variables between production environments drives differences in field performance and soybean yield. These variables may include agronomic history and practices, weather, soil biogeochemistry, and differences in soil microbiome diversity.
Figure 5. Effect size (magnitude of yield differences between microbial treatments and controls). Positive values indicate treatment yield greater than control, and negative values indicate treatment yield less than control. Effect size < 0.2 is considered negligible and effect size = 0.5 is small.
Supplementary Information
Acknowledgements
Dr. Mallory Choudoir (Assistant Professor and Extension Specialist in the Department of Plant and Microbiology) conducted the study and analyzed all results with the help of lab members including Madaris Serrano Perez and Matthew Clayton. The NC State Official Variety Testing (OVT) program and Ryan Heiniger planted and harvested the trial. This work was funded by the North Carolina Soybean Producers Association.
