Buffering and Mitigation of Soil Acidity by Biochar Produced at Varied Temperatures

To investigate the effects of biochar application on the amelioration of acidified soil (Purple soil), biochar derived from cattle manure was prepared at low (300°C) and high (600°C) temperatures. The study utilized acidified soil with five experimental treatments including a control (CK), 1% low-temperature biochar (NF300-1), 2% low-temperature biochar (NF300-2), 1% high-temperature biochar (NF600-1), and 2% high-temperature biochar (NF600-2), over a 90-day indoor cultivation period. The results showed that the specific surface area of NF600 was 9.4 times that of NF300. Compared to NF300, NF600 exhibited an increased carbon content and decreased nitrogen, hydrogen, and oxygen contents. Ratios such as H/C, O/C, and (O+N)/C also decreased, ash content increased by 20.67%, carbonization rate decreased by 19.79%, pH increased by 19.48%, and mineral content increased slightly though the types remained largely unchanged. The application of biochar notably altered the soil's basic physicochemical properties; throughout the cultivation period, biochar addition notably increased soil pH and notably reduced the content of active aluminum, with the 2% high-temperature biochar (NF600-2) showing the most pronounced effects. By the 90th day, compared to the control, soil pH had increased by 23.69% and active aluminum content had decreased by 47.79%. Additionally, biochar application notably enhanced soil conductivity, although this effect diminished over time. Overall, the application of 2% biochar showed a notably better amelioration effect on acidic soils compared to 1%, and biochar produced at a pyrolysis temperature of 600°C was more effective than that produced at 300°C.