The NC State Soil Microbiome Extension program conducted microbial product field trials across North Carolina in 2023. Microbial inoculants are a type of biostimulant comprised of living microbes – bacteria and fungi. Microbial biostimulants can improve plant growth through mechanisms like increased plant nutrient access or enhanced plant stress tolerance. The objective of this study was to evaluate field efficacy of microbial seed treatments on soybean production across North Carolina’s regional environments.

Study Design

Trials were installed at OVT locations in Beaufort County (Tidewater), Sampson County (Coastal Plains), and Union County (Piedmont). See Supplementary Table 1 for soil characteristics and cultural practices and Supplementary Figure 1 for 2023 weather data.

Three microbial seed treatments (Table 1) plus a non-treated control were installed at each location in a randomized plot design (4 x 20 ft rows with 15” row spaces) with 4 replicates per treatment. Product application rates followed manufacturer’s instructions, with a total application volume of 5 fluid oz/100 lbs of seed (volume adjusted with DI water). Seeds were planted within 5 days of treatment. We treated two soybeans varieties: Asgrow Bayer Crop Sciences AG52XF0 (MG 5.2) and AG59XF0 (MG 6.1) which are XF/SR (trait) and pre-treated with Acceleron Fungicide and Insecticide.

Table 1. Microbial seed treatment label information. *Microbial species are bacterial unless indicated as fungal (F). **Stabilize RZ is recommended as a soil amendment/in-furrow application, and the seed application in this study is exploratory. cfu = colony-forming units, vp = viable propagules

Results

Soybean yield differs significantly (P<0.001) between locations (Beaufort=67 bu/acre, Sampson=90.5 bu/acre and Union 73.3 bu/acre on average) (Figure 1, Table 2). Within each location, yield differs significantly (P<0.03) between maturity groups (Figure 2). Yield does not differ between microbial seed treatments. There are no significant differences in yield between microbial treatments and non-treated controls within each location and maturity group.

Figure 1. Colored dots show soybean yield (bu/acre) by location for all microbial seed treatments plus non-treated controls. Box plots show the distribution and median yield (gray line) for each treatment. Black dashed lines show the average yield per location and variety/maturity group.

Figure 2. Colored dots show soybean yield (bu/acre) by location and variety/maturity group for all microbial seed treatments plus non-treated controls. Black dashed lines show the average yield per location and variety/maturity group.

Table 2. Soybean yield (bu/acre) per location averaged across 4 plot replicates for varieties AG52XF0 (MG5.2)/AG59XF0 (MG 6.1). NA was due to combine error.

Leaf macronutrients at early growth stage (V4-V5) differed between Beaufort and Sampson locations for nitrogen (P<0.001) and phosphorus (P=0.065) but not potassium (Figure 3, Table 3). Leaf nutrients did not differ between maturity group or microbial treatment.

Figure 3. Box plots show the data distribution and median (black line) of leaf macronutrients (nitrogen-N, phosphorus-P, potassium-K) measured at soybean early developmental stage for Beaufort and Sampson counties.

Table 3. Leaf macronutrients (nitrogen-N, phosphorus-P, potassium-K) measured at soybean early developmental stage (approximately V4-V5) in the most recent mature leaves by NCDA&CS. Union samples were compromised due to heavy rain at collection date.

Summary

• Soybean yield varies between locations. Within locations, yield differs between maturity groups. Yield patterns are consistent with NC State 2023 Soybean OVT yield comparisons.
• Microbial biostimulant seed treatments did not influence yield (or early development leaf nutrients). There was no difference in yield between microbial treatments and non-treated controls.
• Yield values within treatments (including non-treated controls) tend to have a large range or spread. For these small plot trials, a significant difference would require consistent and large increase in yield between treatment and control.
• Environmental variables between production environments drives differences in field performance and soybean yield. These variables may include weather, soil biogeochemistry, and differences in soil microbiome diversity.

Appendix

Supplementary Table 1. Soil chemical and physical characteristics at planting (data from NCDA&CS and NC State EATS Laboratory). Cultural practices and weather data from NC State OVT Soybean 2023 Supporting Data.

Supplementary Figure 1. Full season weather data across locations. Data from NC State OVT Soybean 2023 Supporting Data.

2023-Soybean-Weather-data

Acknowledgements

Dr. Mallory Choudoir (Assistant Professor and Extension Specialist in the Department of Plant and Microbiology) conducted the study and analyzed all results. 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.