2018 ASHS Annual Conference

Commercial microbe-containing crop biostimulants are advertised to maintain or enhance crop growth, perhaps especially under sub-optimal conditions (e.g., drought, nutrient deficiency, high temperature). More than two-hundred such products ranging in composition (e.g., bacterial, fungal, both; cfu/ml) are currently available, complicating product selection. Regardless, to be effective, users must establish and maintain conditions supporting the plant-microbe interactions from which they seek to profit. These conditions are largely unknown, thereby: a) helping to explain the erratic and context-specific outcomes from inoculation in field and high tunnel settings reported to date, b) impeding key research, and c) slowing the transmission of related research-based recommendations for product use, all of which raise serious questions about the product category. In response, a program consisting of ongoing sets of integrated and complementary on-station and on-farm experiments (many involving a citizen-science/farmer-led approach) testing hypotheses specific to the effect of product composition, crop, application timing, application rate, and/or experimental setting on crop yield and quality was developed. Since 2015, program experiments have been completed in seven states (IA, IL, MI, MO, OH, PA, TN), on fifteen farms and two research stations, on seven crops (broccoli, carrot, lettuce, pepper, spinach, squash, tomato) grown in field or high tunnel settings, and with ten OMRI-listed products (Azos Blue, Biogenesis 1 TM NP, BioYield, EcoFungi, Environoc 401, Hydroguard, MycoApply All Purpose Granular, MycoApply Endomax Concentrated WP, Mycogenesis, NP Bioplin). Individual on-station experiments begin spring, summer, or fall with treatment factorials including multiple levels of product (e.g., four-six) and multiple levels of either rate or timing (e.g., seeding, transplanting, after transplanting), with plots arranged in a randomized complete design and applications made as a root-zone drench. On-farm experiments, however, while also collectively completed over much of each calendar year, involve fewer experimental variables and levels of each. To date, outcomes from standard statistical approaches common in product evaluations, variety trials, and cultural management comparisons show that significant increases in yield or quality have been rare, regardless of inoculation parameters or experimental conditions. When found, yield increases were most common following the application of mixed inocula (single products containing multiple species or strains of bacteria, fungi, or both) and typically below eight percent. Analysis of crop data using approaches (e.g., transformation) common in other areas of study in which skewed data are common (e.g., pathology, entomology, weed science) and economic analyses exploring the return on investment from microbe-containing crop biostimulant use are also underway.