Biogas operation parameters are usually optimised to enhance biogas yields while ignoring digestate quality. This study evaluated the effects of varying operation parameters and input feedstocks used in co-digestion with manure on digestate properties and N turnover in soil for 80 days. Net inorganic N release (% of N input) from digestates varied significantly (p < 0.001) due to their contrasting properties. Temperature, hydraulic retention time (HRT), manure type and input feedstocks significantly influenced soil inorganic N release. Animal slurry co-digested with energy crops had the highest average net soil inorganic N release at 67 %, while co-digestion with straw-based feedstock had the lowest at 56 %. Feedstock type greatly influenced the choice of digesting temperature and HRT, with most energy crop-based feedstocks digested at <50 days HRT. Digestate properties NH4+ -N/total N, C/N and total carbon concentration significantly influenced net inorganic N release in soil. A better understanding of the effects of biogas operation variables on nutrient availability and digestate fertilising properties could help design and optimise the anaerobic digestion process to increase biogas yields and N fertiliser value of the digestates.