Soybean yield response to biostimulant seed treatments in Brazil and the United States: A review

Abstract Soybean [ Glycine max (L.) Merr.] farmers have shown increasing interest in using substances or microorganisms purported to enhance plant growth and development as plant biostimulant for seed treatment (BST). Field tests of soybean biostimulants in Brazil and the United States have shown inconsistent results in increasing crop yield. Additionally, there are substantial differences in the BST registration and regulation processes in Brazil compared to the United States. Therefore, the objectives of this literature review are to (1) synthesize published research articles on the influence of biostimulant products that contain the commonly used microorganisms of the genera Azospirillum, Bacillus , and Bradyrhizobium for seed treatment on soybean seed yield in Brazil and the United States and (2) compare the BST registration differences between the two countries. After synthesizing 40 papers, we found that biostimulants more frequently increased soybean yields in Brazil compared to the US field trials. One existing limitation is the absence of a clearly defined, unified, science‐based regulatory pathway for BST products in the United States. Thus, the lack of regulation in the United States opens space for commercializing products without supporting data. In Brazil, the Ministry of Agriculture and Livestock has established legislation for registering, producing, and commercializing BST. Overall, some of the inconsistent benefits identified in the US literature may be partially attributed to the need for improvements in product registration and quality tests. Additionally, the quality tests should be not only at the microbiological level but also at the agronomic level using research‐based evidence from independent field trials.