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Biostimulant strategies to enhance performance and quality of Italian ryegrass (Lolium multiflorum) William Kenneth O'Neill (24169584) PUREID: 630853789 Microbial biostimulants biostimulant sustainable agriculture Italian ryegrass phosphate solubilisation plant growth promoting rhizobacteria mesocosm trial field trial abiotic stress tolerance. In recent years, there has been a growing interest in biostimulant strategies aimed at enhancing the productivity and quality of agricultural crops. Among these strategies, the use of phosphate-solubilising bacteria, particularly Bacillus amyloliquefaciens, has shown promise. However, there exists a significant knowledge gap concerning the application of this microbial biostimulant in water or slurry alongside standard fertilisation practices to enhance Italian ryegrass (Lolium multiflorum) productivity and quality. Sustainable agriculture demands innovative strategies to enhance crop resilience and productivity while minimising environmental impact, particularly under the constraints of global climate change and resource depletion. This thesis presents a multi-layered investigation into the application of the commercial bacterial biostimulant, ‘Biomex starter’, containing B. amyloliquefaciens FZB42, focusing on its characterisation, impact on nutrient uptake, and the potential to improve the sustainability of Italian ryegrass cultivation. Through a combination of laboratory-based characterisation, controlled large-scale mesocosm, and field trials, this study clarifies the contribution of microbial biostimulants to the advancement of environmentally friendly agricultural practices. Chapter 2 focuses on the molecular identification and functional characterisation of ‘Biomex starter’. Utilising MALDI-TOF MS and 16S rRNA gene identification, the study validates the biostimulant’s claims and evaluates its resilience to environmental stressors, including temperature, pH, salinity, and drought. The adaptability of B. amyloliquefaciens FZB42 to diverse carbon (C) and nitrogen (N) sources is explored, demonstrating its capacity to endure and function under fluctuating environmental conditions. This chapter establishes a benchmark for microbial biostimulant validation, advocating for rigorous genetic and bioactivity assessments to foster consumer confidence and standardize market offerings. Chapter 3 examines the influence of B. amyloliquefaciens FZB42 on the root-to-shoot resource allocation in Italian ryegrass growing in phosphorus (P)-deficient soils. Through large-scale mesocosm trials, the research assesses the biostimulant’s efficacy in enhancing plant growth productivity and nutrient uptake. The findings show an increase in shoot and root biomass, particularly when the biostimulant is applied in a water carrier along with standard synthetic fertilisation practices. The treatment notably benefits tetraploid cultivars and is linked to higher chlorophyll content and P offtake, which are crucial for forage quality and efficiency in grassland management. Chapter 4 investigates the sustainability of Italian ryegrass by evaluating the effects of inoculating B. amyloliquefaciens FZB42 on an existing third-year ley under Northern Irish climatic conditions. This study compares the dry matter yields and mineral quality of Italian ryegrass. The data demonstrate that Italian ryegrass maintains high yields and nutrient content into the third year, with biostimulant application further influencing its performance. These findings suggest that Italian ryegrass remains competitive with other ryegrass species. Synthesising the findings from these investigations, the thesis highlights B. amyloliquefaciens FZB42 as a promising agent with potential applications in sustainable agriculture. While it demonstrated the ability to stimulate plant growth and enhance nutrient uptake under controlled mesocosm conditions, these benefits did not fully translate into yield improvements in field trials. This discrepancy emphasises the complexity of real-world agricultural systems and the need for further research to optimise biostimulant efficacy under variable field conditions. The outcomes of this study contribute valuable insights into the application of microbial biostimulants, providing practical knowledge for researchers and informing future strategies for their use. Rather than advocating for immediate adoption, the thesis highlights the necessity of context-specific application strategies, ensuring that biostimulant use aligns with both environmental sustainability and economic viability in practical farming systems. Thesis is embargoed until 31 July 2027. 2026-10-01T16:28:12Z Text Thesis 10.17034/32640789.v1 https://figshare.com/articles/thesis/Biostimulant_strategies_to_enhance_performance_and_quality_of_Italian_ryegrass_i_Lolium_multiflorum_i_/32640789 All Rights Reserved Open Access after 2027-07-31