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Substitution of mineral fertilizers with organic soil amendments is postulated to improve productivity-relevant soil properties such as aggregation and organic matter (OM) content. However, there is a lack of studies analyzing the effects of biochar and biogas digestate versus mineral fertilizer on soil aggregation and OM dynamics under temperate field conditions. To address this research gap, a field experiment was sampled four years after establishment on a sandy Cambisol in Germany where mineral fertilizer or liquid biogas digestate was applied with or without 3 or 40 Mg biochar ha(-1) (produced at 650 degrees C). Soil samples were analyzed for soil organic carbon (SOC) content, pH, cation exchange capacity, bulk density, water-holding capacity, microbial biomass, aggregate size class distribution, and the SOC content associated with these size classes. 40 Mg biochar ha(-1) significantly increased SOC content in all fractions, especially free particulate OM and the 2-0.25 mm fraction. The yield of small macroaggregates (2-0.25 mm) was increased by biochar, but cation exchange capacity, water-holding capacity, and pH were not consistently improved. Thus, high-temperature biochar applied to a sandy soil under temperate conditions is primarily recommended to increase SOC content, which could contribute to climate change mitigation if this C remains sequestered over the long-term. Fertilizer type did not significantly affect SOC content or other measured properties of the sandy Cambisol, suggesting that replacement of mineral fertilizer with digestate has a neutral effect on soil fertility. Co-application of biochar with digestate provided no advantages for soil properties compared to co-application with mineral fertilizer. Thus, independent utilization of these organic amendments is equally suitable.