Foliar application of iron strengthened- artificial humic acid promotes nitrogen fixation and improves soybean yield

Soybeans and nitrogen-fixing bacteria have evolved complex symbiotic relationships to form nodules that fix nitrogen from the atmosphere, providing for host plants. In this study, the effects of different concentrations of Fe-catalyzed artificial humic acid liquid fertilizer (Fe-AHA) on soybean growth were investigated. Compared with commercially available Fe fertilizer, Fe-AHA 20 treatment significantly increased the shoot and nodule biomass of soybean by 16.24 % and 22.68 %, and increased the content of nodule ureide by 47.97 % and the activity of nitrogenase by 25.57 %. The transcriptomic and metabolomic analyses showed that Fe-AHA 20 promoted nodule carbon assimilation to provide more energy for nitrogen fixation, activated antioxidant system to eliminate excess reactive oxygen species, and regulated the expression of signaling factors to promote nodule development. Fe-AHA 20 also increased soybean yields by 27.56 % compared to Fe-EDTA and improved the nutritional quality of seeds. Our study provides an effective strategy for promoting soybean growth and improving soybean yield and quality. • Foliar spraying of Fe-catalyzed AHA could effectively supplement iron in soybean. • Fe-catalyzed AHA can improve the nitrogen fixation ability of soybean, promote soybean growth and increase soybean yield. • Transcriptomics and metabolomics were used to analyze the mechanism of Fe-catalyzed AHA promoting soybean growth.