Effect of Foliar Treatment with Aqueous Dispersions of Silver Nanoparticles on Legume-Rhizobium Symbiosis and Yield of Soybean (Glycine max L. Merr.)

Interest in the use of silver as a component of plant protection products and growth regulators appeared relatively recently with the development of methods for the effective stabilization of colloidal systems containing nanoparticles of this metal. In the present work, we studied the effect of foliar treatments with aqueous dispersions of silver nanoparticles stabilized by polyhexamethylene biguanide hydrochloride with an average diameter of 6 ± 1 nm and a zeta-potential of +47.4 ± 1.3 mV on legume-Rhizobium symbiosis, which largely determines the efficiency of soil nitrogen assimilation and the yield of soybean (Glycine max L. Merr.). Based on the results of a two-year field experiment, it was shown that treatments with low doses of silver nanoparticles lead to a significant increase in the number of root nodules and an increase in soybean yield. The observed biological effectiveness of silver nanoparticles dispersions is explained by an increase in the enzymatic activity of peroxidases and polyphenol oxidases in the terrestrial part of plants. It is very likely that the treatment with silver nanoparticles and the increase in peroxidase activity in non-infected parts of the plant lead to a more effective prevention of the penetration of rhizobacteria into the aboveground soybean organs, which, in turn, may be the reason for the observed decrease in the activity of peroxidase and polyphenol oxidase in parts of plant roots susceptible to rhizobia. The latter, as is known, contributes to an easier flow of the nodulation process and the development of legume–Rhizobium symbiosis.