Effect of anaerobic digested sludge biochar on soil quality improvement: An insight into mechanisms, microbial composition, and toxicity risk assessment

Abstract

Biochar is widely acknowledged for its remarkable impact on soil conditioning. However, the influence of different sources of biochar, particularly anaerobic digested sludge biochar (ADBC) derived from anaerobic digested sludge and biochar derived from waste activated sludge, on alkaline soil remains largely unexplored. To address this knowledge gap, a comprehensive field experiment was conducted over a period of 180 days to investigate the effects of ADBC on slightly alkaline soil. This study evaluated various aspects, including soil properties, nutrient content, microbial composition, and soil toxicity. The results demonstrated significant improvements in the quality of alkaline soil following the application of ADBC. Notably, soil pH decreased from 8.24 to 7.5, while conductivity increased from 56.7 μs/cm to 249.0 μs/cm, total organic carbon from 13.5 g/kg to 19.9 g/kg, available nitrogen from 45.5 g/kg to 237.5 g/kg, and available phosphorus from 549.5 g/kg to 1396.7 g/kg. Moreover, ADBC substantially increased the relative abundance of functional bacteria associated with nutrient cycling, such as Proteobacteria, Actinobacteriota, and Bacteroidota. Conversely, the assessment of biotoxicity revealed a decrease in toxicity with increasing preparation temperature and particle size. These findings highlight the promising potential of ADBC for improving the key properties of alkaline and nutrient-poor soils crucial for overall soil productivity.