Microbial species that fix atmospheric nitrogen can benefit plants by colonizing the area around the roots or internal plant tissues and increasing nutrient availability. This process can reduce the need for synthetic fertilizers, therefore maintaining healthy soil and promoting environmental sustainability. Three endophytic bacterial species (Herbaspirillum, Gluconacetobacter, Methylobacterium) are gaining attention as potentially effective plant growth promoters when applied to the leaves directly, whereas an associative species Azospirillum is conventionally applied to soil. This field study investigated the impact of the foliar application of these four bacterial species independently and in combination, on the growth, physiological performance, and yield of corn and soybean. Overall, corn plants treated with the endophytic bacteria had increased leaf nitrogen content, chlorophyll, and greater reproductive yield compared to the untreated plants. However, the associative Azospirillum showed no growth benefits. In soybean, chlorophyll content was enhanced when all microbe species were combined in mixture, while seed mass was increased under only some of the endophytic microbes compared to the control. These results suggest that foliar treatments could be effective when using bacterial species classified as endophytic for boosting crop productivity, offering a more environmentally friendly way to supply nitrogen to plants than conventional synthetic fertilizers.
