Organic Broadcaster

Researchers share five ‘fast facts’ to help growers understand biofertilizers

By Matthew D. Kleinhenz,  The Ohio State University

An increasing number of products containing microbes as
the primary active ingredient are being marketed to growers looking to enhance: a) crop growth, b) nutrient acquisition, uptake, or utilization, c) tolerance to stress (e.g., temperature, moisture), and/or d) yield. However, the effectiveness of many products is undocumented, leaving growers and advisors to assess efficacy and potential product return on investment.

A team led by The Ohio State University is assisting with that process by conducting on-station and on-farm evaluations and creating resources and educational opportunities helping guide product selection, use, and evaluation. Products are tested under a range of conditions – so far, 21 sites over seven states have been employed in experiments involving seven crops, 13 products, and 10 companies. For details, see

Microbe-containing crop biostimulants or biofertilizers are popular among growers and a growing source of revenue for product manufacturers and suppliers. Yet, many questions are unanswered. How should they be used? Are they effective? Do they offer a consistently positive return on investment? While more research is needed to address these questions in detail, the following five “Fast Facts” can help growers make informed decisions about using these products.

Fact One: They are numerous and diverse in important ways. We have tracked the number of these products and companies offering them since March 2015. Currently, we know of 247 OMRI-listed microbe-containing crop biostimulants offered by 105 companies in the U.S.1 The number of products and companies in this category have risen 1.6- and 1.5-fold, respectively, in three years. Also, individual products contain either an array of microbes (e.g., multiple types of bacteria, fungi, or both) or a much smaller subset (e.g., single species of bacteria). Some products also contain components designed to feed the microbes, crop, or both.

Fact Two: Overall, labeling and third-party documentation of efficacy are weak. Compared to fertilizers, biopesticides, and other inputs, regulation of microbe-containing crop biostimulants is minimal and inconsistent, with much state-to-state variation. Labels can lack complete or accurate descriptions of package contents or detailed instructions for use. Currently, there is no systematic, third-party, state, regional, or national testing system or mechanism for developing efficacy information (unlike for biopesticides). Companies appear to differ significantly in the amount and rigor of third-party testing they conduct. As one consequence of this “Wild West” scenario, the best evidence of efficacy on farms is often not publicly available since farmer-focused, research-based reports featuring these products are rare.

Fact Three: They are increasingly popular among organic and other growers in the U.S. and globally. Projections are for the U.S. biofertilizer market (including products in which “microbes do the work”) to reach approximately $250 million in revenue in 2022; globally this number is $2.3 billion.2 A survey of Organic Systems Plans covering 2009-2014 in Ohio revealed that biofertilizers and biopesticides accounted for 9% by number of all inputs on these farms.3

Fact Four: Biological and procedural factors may limit the efficacy of microbe-containing crop biostimulants. For example, potential host-specificity dictates that microbes in the products may form productive associations with only certain crops or associations with some crops may be more productive than with others. Competition with other microbes, predation, stress, and other factors may limit inoculant activity. Also, the influence of soil type, application regimen (timing, rate, method, placement), and other inputs on efficacy is unclear for many products. Understanding those influences more thoroughly requires time, effort, care, funds, and cooperation given the number of products, the diversity of their microbial contents, and the range of the conditions under which they are used. With support from USDA, SARE, various companies, and others, we and our collaborators work to develop resources that lessen some of the mystery around selecting, using, and evaluating microbe-containing crop biostimulants.

Fact Five: Ways in which these products work (modes of action) can lead to application effects being more subtle than with other inputs. Inoculated plants may grow a little faster, flower a little sooner, and appear to be healthier (e.g., in color) in a range of conditions but not yield considerably more. Of course, these differences will be apparent only when an untreated check area is available for comparison. Regardless, documented inoculant effects will allow users to know exactly what they can/should expect from a product and to be certain it is what they want to pay for.

These simulated plots represent results from two typical scenarios, A and B (left and right). Both scenarios result in the same average yield increase, but Scenario B may be more favorable to the grower. The position of the upright line shows that yield increases occurred in far more cases in Scenario B than in A, as depicted by the location of the upright line connecting the trial axis to the dashed average line. The yellow rectangle around the average line represents the variation in yield increases; it is thinner in Scenario B, also a plus for product users and their advisors.


In replicated trials, statistically significant yield increases are rare and usually don’t exceed 6-7%. It’s common to see a range of responses to inoculation with a single product—over different trials in different seasons and involving different crops. Companies and investigators may consolidate responses from many trials into graphs resembling ones in the figure. The shape of the graph for a product is at least as important to growers as the average yield response, which is the most commonly reported statistic. The shape of the graph and, by association, the most frequently occurring yield response, may be a more reliable indicator of what growers should expect from the product. So, when inquiring about a product, consider asking for either the distribution of yield responses across trials and/or the most frequently occurring yield response, in addition to the average.There is a tangible, justifiable, and widespread enthusiasm for the idea that purposeful inoculation of seeds, crops, and/or soils with beneficial microbes (e.g., bacteria, fungi) may enhance farm success and environmental stewardship. Inoculation would complement steps fostering the development and activity of naturally occurring, beneficial microbial communities. Being enthusiastic about opportunities created by inoculation is easy: so far, it rarely results in lower yield, it may result in higher yield, and it is often thought of as “cheap enough.”

However, the goal is to ensure that inoculation offers more growers a greater return on investment more often. Achieving that goal definitely requires more information and it may require better products.

Based on these five fast facts, researchers offer these recommendations: First, stay tuned to reports from the microbe-containing crop biostimulant industry and trusted sources; second, experiment with biostimulants using reliable guidelines—such as SARE’s How to Conduct Research on Your Farm or Ranch4—and engage with others involved in this research. The Ohio State University Vegetable Production Systems Laboratory manages a listserv for vegetable producers to share information and field experiences with microbial-based biostimulants. To join, see



Matthew Kleinhenz is a professor in Horticulture and Crop Science at The Ohio State University, Wooster, Ohio. Julie Laudick, Stephanie Short, Zheng Wang, and Nicole Wright contributed to the content of this article.



3. Laudick, J. et al. 2016. M.S. Thesis, The Ohio State Univ.; Microbial biostimulants in organic farming systems: patterns of current use and an investigation of their efficacy in different soil environments.





From the July | August  2018 Issue


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