Pre-sowing protection of inoculated soybean Glycine max (L.) Merr. seeds by water-soluble polymer compositions and their solid-phase modification

The effectiveness of some water-soluble polymers as film-forming agents that provide better adhesion of bacteria to seeds (like multicomponent formulations in modern chemical dressings) remains practically relevant. The likely candidate adhesives are low and high molecular weight sodium alginate (FMC polymer), hydroxypropyl methylcellulose (HPMC) (Colorcon®, Colorcon, Inc., USA), polyethylene glycol (PEG), carbomer-carbopol 940 (Necardis SA), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (povidone, PVP) (K15). Film-forming polymers can also improve the shelflife of biologicals, their compatibility with chemical protective agents and resistance to UV radiation, temperature extremes and drying, thus increasing survival of bacteria on the surface of inoculated seeds. These allow practitioners to carry out seed pre-sowing inoculation beforehand. Developed polymer compositions should be more effective than single-component, provided that they remain cost-effective and convenient for practical use. This paper is the first to report the effects of various polymer combinations on inoculated seeds and the improvement of protective properties of the water-soluble polymers by activated charcoal, a solid-phase component. Among the polymers tested, polyvinylpyrrolidone is revealed to be the most effective for rhizobial survival due to longer allowable interval between seed inoculation and sowing. Our objective was to compare survival rate of Bradyrhizobium japonicum 634b inoculum for soybean cv. Belgorodskaya 7 seeds as influenced by water-soluble polymers polyvinylpyrrolidone, polyvinyl alcohol, sodium alginate and carboxymethylcellulose as additives. Our findings indicate that 10 % polyvinylpyrrolidone solution is the most effective among the studied polymers. Its use increases more than 10-fold the survival of nodule bacteria on seeds 10 days after inoculation of seed material. Variants with different concentrations of carboxymethyl cellulose and sodium alginate do not ensure bacterial survival on seeds for more than 3 days. It is possible to create an effective polymer-carbon composition with a lower concentration of polyvinylpyrrolidone (7.5 % polyvinylpyrrolidone and 5.0 % activated charcoal). This composition is more effective than polyvinylpyrrolidone without coal, and provides a 20-30 % reduction in bacterial death on inoculated seeds after the first 5-7 days of seed storage.