Presowing Management as a Factor Influencing Vegetative, Reproductive, and Biochemical Performance in Soybean Seed Production

Although chemical, biological, and vitamin-based seed treatments are individually well documented in soybean, comparative evidence on their combined application within a single experimental framework remains scarce. This study evaluated the effects of treating soybean seeds with a chemical product, Azospirillum spp. (2 mL kg–1 of seed), and the B-complex vitamins pyridoxine (B6) and nicotinamide (B3) (100 mg kg–1 of seed), applied alone and in combination, on gas exchange, vegetative growth, reproductive performance, and seed biochemical composition of soybean grown under greenhouse conditions. Seed treatments altered intercellular CO2 concentration and increased carboxylation efficiency, without significantly affecting net photosynthesis, stomatal conductance, transpiration, or water use efficiency. Treated plants showed greater plant height, branching, and pod number, together with higher seed number and mass, with Azospirillum spp producing the most consistent gains. Protein, lipid, amino acid, and soluble sugar contents increased with seed treatment, while proline remained unchanged, indicating a beneficial physiological stimulus rather than a stress response. These findings show that combining chemical, biological, and vitamin-based seed treatments improves vigor and early performance in soybean seed production and provide a practical basis for developing multi-input seed treatment protocols, although validation under field conditions is still required.