Multi-Species Microbial Inoculants Enhance Turfgrass Quality, Nutrient Uptake, and Stress Resilience Under Temperate Polish Conditions

Sustainable care of urban lawns requires methods that maintain high turf quality while reducing the use of chemical fertilizers. The objective of this three-year field study was to evaluate whether microbial inoculants can complement or partially substitute conventional fertilization (65–190 kg N·ha−1, 33–35.2 kg P·ha−1, and 124.5 kg K·ha−1) required to maintain high turf quality in an intensively managed lawn system. The experiment was conducted in Poland on a degraded chernozem, classified as Haplic Phaeozem. A standard mixture of perennial ryegrass and fescue was evaluated under four treatments: (1) untreated control; three commercial microbial formulations: (2) StymGrass P+K, containing nutrient-solubilizing Bacillus spp.; (3) BioVitaGrass, combining Bacillus spp. with arbuscular mycorrhizal fungi (AMF); and (4) NitroGrass, containing nitrogen-fixing Azotobacter spp. with Bacillus spp. All microbial treatments improved lawn quality compared with the untreated control. Lawns receiving BioVitaGrass or NitroGrass showed the strongest responses, including denser plant cover, greener and finer leaves, reduced disease symptoms, and increased concentrations of nutrients in the plant tissue. StymGrass P+K produced smaller but still positive effects. Measurements of plant conditions, such as leaf greenness and canopy development, also indicated improved photosynthetic activity in inoculated plots. These results support the role of plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi in nutrient mobilization, root stimulation, and stress resilience. Although most evidence comes from crops, this study provides novel field-based confirmation of multi-functional microbial inoculant efficacy in turfgrass under this study’s conditions.