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Anaerobic digestate biochar and soil health: a laboratory and field experiment approach testing impacts on grassland production Henry McGuiggan (24304583) PUREID: 690051018 Anaerobic digestion Biochar Belowground biodiversity Carbon sequestration Climate-smart agriculture GHG mitigation Nutrient cycling Soil microbiome Agriculture must simultaneously enhance soil health, reduce greenhouse gas (GHG) emissions, improve nutrient-use efficiency, and contribute to climate mitigation within planetary boundaries. This thesis evaluated anaerobically digested poultry litter (ADPL), ADPL-derived biochar, and nitrogen-enriched biochar across field, greenhouse, and laboratory experiments in temperate grassland systems representative of the UK and Ireland. A randomized block field experiment compared ADPL, biochar, biochar+N, slurry, inorganic fertiliser, and untreated controls using analyses including generalized linear mixed models (GLMMs), principal components analysis (PCA) and phospholipid fatty acid (PLFA) profiling. ADPL more than doubled grass yield relative to biochar alone and increased grass uptake of NPK, Mg, S, and Ca, while improving soil Mg and S. Unamended biochar had limited short-term agronomic effects, whereas biochar+N achieved fertiliser-equivalent yields while enhancing soil pH, nutrient retention, carbon storage, and micronutrient status. Field GHG measurements suggest that digestate-derived biochar produced lower CO₂-equivalent emissions, relative to ADPL, slurry, and fertiliser. Nitrogen enrichment increased N₂O emissions, partially offsetting this mitigation benefit. Belowground biodiversity appeared resilient to soil amendment effects within one year of first application; across microarthropods and nematodes, no substantive treatment effects were detected. Contrastly, microbial communities responded strongly to nutrient chemistry. PLFA analyses showed organic amendments, including biochar, supported more balanced microbe communities with more gram-negative bacteria and arbuscular mycorrhizal fungi, whereas fertiliser and biochar+N favoured gram-positive bacteria and Actinomycetes associated with rapid nutrient turnover. A factorial pot experiment demonstrated that biochar’s primary agronomic value was structural rather than nutritional, enhancing the performance of co-applied organic and mineral nutrients. Finally, slurry-storage experiments suggested that biochar had little effect on total GHG or NH₃ emissions but eliminated dangerous hydrogen sulfide (H₂S) at medium-to-high application rates potentially reducing health risks. Collectively, these findings support biochar as a multifunctional tool for climate-smart grassland management, nutrient recycling, carbon sequestration, and improved agricultural resilience.<br><br><i>Thesis is embargoed until 31 July 2028.</i> 2026-10-01T16:08:29Z Text Thesis 10.17034/32826368.v1 https://figshare.com/articles/thesis/Anaerobic_digestate_biochar_and_soil_health_a_laboratory_and_field_experiment_approach_testing_impacts_on_grassland_production/32826368 All Rights Reserved Open Access after 2028-07-31