Synergistic Effects of Microbial Inoculant and Biostimulant Seed Treatments on Winter Wheat Yield Under Variable Moisture Conditions

Improving the productivity and stability of winter wheat under increasingly variable climatic conditions remains a major challenge for sustainable agriculture. This study evaluated the effects of pre-sowing seed treatment with a microbial preparation (Nando BioExpert) and a biostimulant (Vitazyme), applied individually and in combination, on crop establishment, yield components, and grain yield of winter wheat under unstable moisture conditions in the Right-Bank Forest-Steppe of Ukraine. A three-year field experiment demonstrated that both treatments positively influenced plant growth, while their combined application produced a pronounced synergistic effect. Seed treatment enhanced plant establishment, increasing plant density at emergence from 242 plants m−2 in the control to 372 plants m−2 under the combined treatment. This improvement contributed to increased stand-level productive tiller density per unit area. Consequently, grain yield was consistently improved across years, with the combined treatment producing the highest average yield (6.04 t ha−1), corresponding to a 37% increase relative to the control. The results indicate enhanced winter wheat resilience to environmental stress under biological seed treatment. Overall, integrating microbial inoculants with biostimulants represents an effective strategy for improving winter wheat productivity under moisture-limited conditions and supports the transition toward sustainable and resource-efficient crop production systems.