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Strategic Farming: Let’s talk crops! session talks biologicals on corn and soybean

minnesota soy
Photo: Claire LaCanne

By Angie Peltier, UMN Extension crops educator, Seth Naeve, UMN Extension soybean agronomist and Daniel Kaiser, UMN Extension soil fertility specialist

On February 8, 2023, Seth Naeve, Ph.D., UMN Extension soybean agronomist and Daniel Kaiser, Ph.D., UMN Extension soil fertility specialist, joined UMN Extension crops educator Lizabeth Stahl for a conversation about the latest research on biologicals for corn and soybean. This was the fifth episode of the 2023 Strategic Farming: Let’s talk crops! webinars in this series.

To watch this episode:

Biological seed treatments for soybean

In recent years, the marketplace of biological products on the market has been growing and is projected to be a $12-13 billion industry in the US by 2024. Biological seed treatments claim to improve nitrogen (N) fixation, assimilate organic and inorganic phosphorus (P), increase nutrient use efficiency or uptake, stimulate root growth or expand root absorption, control pathogens or elicit a plant immune response. 

Field trials

To identify situations where biological seed treatments improve soybean yield and profitability and improve nutrient status, a series of uniform field trials have been conducted by university-based soybean agronomists (including Seth Naeve) throughout the Midwest evaluating soybean seed treatments. A total of 9 different fungal or bacterial biological seed treatments from large, reputable national or international companies and an untreated control were tested on locally adapted soybean varieties grown as close to the way that local farmers produce soybeans (including using other commonly used seed treatment a.i.’s). In 2022, data was collected from small plot randomized, replicated (6-8 reps) trials in 17 states for a total of 50 site-years. This project will be continued in 2023. The higher than typical number of replications were included to better pick out small differences among treatment yields. Seed treatment label instructions were also followed, and applications were made within 24 hours of planting to ensure viability.

Three of the 10 trial locations in Wisconsin (Arlington, Clinton and Eau Galle) had statistical differences among treatment yields, with individual biological treatments out-yielding the untreated control at two of the locations and the untreated control out-yielding biological seed treatments at the other. One location in Renner, SD had statistically significant differences among treatments, but in this case the untreated control actually out-yielded many of the plots planted to seed with a biological treatment. Expecting to see some very positive effects with biologicals, the research team was surprised that they saw positive yield responses to biological seed treatment at so few sites. From a statistical analysis standpoint, researchers often present data that they are 95% confident are a result of treatment effects and not simply random chance; with a 5% chance of seeing a false positive yield response, with 50 site-years, the team would have expected at least 2.5 sites to have a positive yield response regardless of biological seed treatment, or 0.5 more statistically positive yield responses to biologicals than was actually observed.

Despite the trial results, Naeve hopes to find products that work for US farmers, but cautions that products are unlikely to work on every acre (due to physical location and soil chemistry) and that more data is required to find effective treatments and the scenarios under which they are more likely to succeed, as these products are unlikely to perform well under all soil conditions, from very wet to very dry, from very low to very high soil pH.

A regional committee to study biostimulants

Biostimulants are substances (or microbes) that promote plant growth at small quantities; fertilizers, pesticides and soil conditioners are not considered biostimulants. Biostimulants, including humic or fulvic acids (long-chain organic acids), have shown some positive responses in potato in low organic matter soils in the western US. However, in our comparatively higher organic matter soils, these products tend to be overwhelmed or outcompeted by native microbes already present in the soil. Other biostimulants include N-containing compounds such as amino acids and chitosans (made from shrimp shells) and seaweed extracts. After various unregulated products had begun to be heavily marketed, in 1980 a regional committee of university-based scientists (called NCR-103 or NCERA 103) was developed to test marketing claims.

Biological seed treatments for corn

In recent years, molecular biological tools are no longer cost-prohibitive, leading to soil, plants, plant residue and composted manure being analyzed for candidate biostimulants – leading to a tsunami of products coming onto the market. In corn production, the most abundant biostimulant products are free-living fungi or bacteria that colonize the soil around the roots where they consume organic acid compounds exuded by roots. Their growth-habit tends to be quite different than rhizobium bacteria that live inside root nodules.

Mycorrhizae are fungi that form specific symbiotic relationships with roots of more than 90% of terrestrial plants, growing both within and between root cells and into the soil. These fungi essentially extend the root system and help the plant to improve water, P and zinc uptake.

Some bacterial species are free-living (not associated with the plant) and fix atmospheric N into a plant-available form. One species (Azospirillium) is capable of supplying 7-12% of the N needed by wheat. However, as these products (when combined with mineralized N) are unlikely to provide a crop’s total N need, synthetic N fertilizers will also need to be applied. As observed with the rhizobium N-fixing bacteria, N fixation tends to decline when inorganic N is supplied.

Is inoculation with bacteria beneficial?

Results of field studies with biostimulants (including microbes) have been inconsistent. This is theorized to be due to the fact that bacteria that are applied as biostimulants need to compete with the estimated 1 billion bacteria already living in each teaspoon of soil. These pre-existing soil bacteria evolved in that environment and so may be better adapted to those soil conditions. From a numbers standpoint alone, it is easy to see how an amended biostimulant may be easily overwhelmed by pre-existing bacteria. The Kaiser lab tested a bacterial product called ProveN at six locations from 2019 through 2021. At only one location-year (Waseca-2020) was there a positive yield response with this product; supplying approximately 20 lbs of N in field quite responsive to N fertilizers.

Recommendations for on-farm testing of products marketed to supply N

Below are recommendations for setting up a successful experiment to determine whether a biological product marketed to supply N holds up to marketing claims:
  • Replicate treatments: have multiple strips of a particular treatment in the field; 3 is ok but may not be able to pick apart small yield differences among treatments, 4 or more is better.
  • Randomly assign treatments throughout the field (don’t just split a field).
  • Treatments should include:
    1. the N-rate needed by the crop,
    2. a slightly lower N rate (~30 lbs less) than is needed by the crop + the biological marketed to supply N
    3. a slightly lower N rate (~30 lbs less) than is needed by the crop
Only comparing treatment 1 and 2 wouldn’t really reveal whether the biological marketed to supply N is responsible for the result or whether the N mineralized from organic matter in the soil or an “aggressive” N rate (even when 30 lbs are omitted) is responsible. Only by including all three treatments can one tell what is causing any observed yield response.

Fielding audience questions

Kaiser and Naeve answered numerous audience questions including: does coating urea with humic acid act as an effective urease inhibitor? how do small plot research results relate to what I would see on my own farm? if producers work to improve soil health qualities, would they really need these biologicals? looking ahead, are there any products showing promise and agreeing with company claims? do you also see the lack of response to biologicals as a plant problem (ie. can crops be bred to better form a symbiotic relationship with some of these biologicals)? what about post-emergence applied biologicals?

Thanks to the Minnesota Soybean Research & Promotion Council and the Minnesota Corn Research & Promotion Council for their generous support of this program!
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