Biogas Slurry Application Is Linked to Higher Soil Multifunctionality and Specific Microbial Communities in Orchards

Anaerobic digestion of livestock manure has become increasingly widespread, producing biogas slurry that is widely used as a nutrient‐rich fertilizer. However, temporal changes in soil nutrients, soil functions, and crop quality associated with biogas slurry application have yet to be fully understood. Here, using a space‐for‐time design, we compared orchard soils receiving biogas slurry with those receiving conventional fertilization within a standardized ecosystem multifunctionality assessment framework. To examine patterns associated with the duration of biogas slurry application, we included orchards with 1, 2, and 4 years of biogas slurry application. Moreover, microbial communities were profiled using high‐throughput sequencing to explore their associations with soil multifunctionality. The results showed that biogas slurry‐amended orchards had a significantly higher soil fertility index than conventionally fertilized orchards. Orchards with 4 years of biogas slurry application exhibited the highest soil multifunctionality. In addition, the relative abundances of taxa across different microbial network modules differed among orchards with different fertilization histories. Structural equation modeling revealed that variation in soil multifunctionality was associated with shifts in microbial modules dominated by Candidatus_Udaeobacter (bacteria) and Fusarium (fungi), together with differences in the soil fertility index. Overall, plots with a history of biogas slurry application exhibited higher soil multifunctionality than conventionally fertilized plots. Furthermore, specific microbial modules showed stronger associations with soil multifunctionality than the overall microbial community, suggesting that distinct microbial assemblages may be important indicators of multifunctionality across plots with different amendment histories. These insights offer a basis for optimizing organic amendment strategies in sustainable agro‐ecosystem management.