Glyphosate-Induced Hormesis Enhances Soybean Biomass but Not Yield Under Field Conditions in Nebraska, USA

Hormesis, a biphasic dose–response phenomenon, occurs when a low dose of a substance stimulates biological activity of an organism while higher doses inhibit it. Glyphosate, the most widely used herbicide in the United States, has frequently been associated with hormetic effects in certain plant species. The objective of this study was to evaluate whether sublethal doses of glyphosate could enhance soybean growth and yield under field conditions. A two-year experiment was conducted using a split-plot design, with glyphosate applied in seven sublethal doses (0–324 g ae ha−1) at three soybean growth stages: second trifoliate (V2), beginning of flowering (R1), and beginning of pod formation (R3). Growth-related parameters, yield components, and soybean grain yield were evaluated. Exposure to glyphosate at the V2 and R1 stages resulted in hormetic responses, with increase of up to 23% in plant dry matter, 26% in leaf area index, and approximately 60% in the number of branches per plant. No stimulatory effects were observed following R3 exposure. The doses associated with hormesis ranged from 0.65 to 107 g ae ha−1, depending on the response and soybean growth stage. Despite increased growth and biomass accumulation, no enhancement in yield components or soybean grain yield was observed. This study provides field-based evidence of glyphosate hormesis in soybean, contributing to a broader understanding of its agronomic implications and highlighting the complex nature of hormetic responses in agricultural systems.