Reduced tillage and foliar application of Methylobacterium symbioticum synergistically improve yield and nutrient uptake in organic black barley

Sustainable nitrogen management remains a major challenge in organic farming, where plough-based tillage is commonly used to incorporate fertilizers and control weeds, limiting the adoption of reduced tillage systems. Foliar nitrogen-fixing bacteria may offer an alternative nitrogen source that supports simplified soil management while maintaining crop productivity. This study evaluated the effects of soil tillage (ploughing vs. reduced tillage), foliar biofertilisation with Methylobacterium symbioticum (single and double application), and sowing density (350 and 450 seeds m⁻²) on the productivity and nutrient dynamics of organically grown black barley (Hordeum vulgare var. rimpaui). A field experiment was conducted during two contrasting growing seasons (2023–2024) on an organic farm in west-central Poland. Biometric traits, grain yield and its components, and the content and uptake of nitrogen, phosphorus, and potassium were assessed. Weather conditions strongly modified crop responses. Tillage system and biofertilisation exerted the greatest influence on most parameters, whereas sowing density had a weaker effect. The highest grain yield (3.08 t ha⁻¹) was obtained under reduced tillage combined with higher sowing density and a single application of M. symbioticum. Biofertilisation under reduced tillage enhanced grain number per ear, shoot dry matter, and macronutrient uptake, while the absence of biofertiliser increased tissue N and K concentrations but reduced grain size. These results indicate that foliar nitrogen-fixing bacteria can support reduced tillage strategies in organic black barley production. Further research should focus on long-term soil effects and performance under diverse climatic conditions to refine recommendations for organic growers.