This project utilized both field experiment and laboratory analyses to address the gap in understanding regarding the alterations in properties and functions of biochar, and the impact of heavy metal passivation in soil over long-term natural field aging. The study aimed to examine the changes in the physical and chemical characteristics of biochar over an extended period of natural aging. Additionally, it sought to analyze the impact and mechanisms of biochar in reducing of the harmful effects of the heavy metal cadmium (Cd) during the aging process. Both original and aged biochar conformed to the pseudo-second-order kinetics model and the Langmuir model. The aging process enhanced the adsorption of Cd by biochar and mitigated the leaching of Cd²⁺ into the soil. These findings provide a scientific basis for evaluating biochar’s environmental behavior and its potential use in the remediation of soil contaminated with heavy metals.

Tea plantations commonly receive substantial quantities of nitrogen (N) fertilizer, with potential for considerable N loss to occur. This study assessed N retention in acidic tea plantation soil and examined how different biochar application rates and fertilizer combinations affect N dynamics, highlighting the importance of innovative technologies to monitor and enhance N supply management. This research adopted a modified 2-week aerobic incubation and ion-exchange membrane (IEM) techniques to evaluate the soil N supply in tea plantations following early-summer top-dressing as influenced by various biochar rates and fertilizer combinations. We quantified the amount of mineralized N in acidic tea plantation soils during the summer. Our results show that biochar enhances soil N supply not by increasing N mineralization directly but by improving soil mineral N retention. Notably, a threshold effect was identified at biochar application rates of 20–30 tonnes ha⁻¹. The window for maximizing the effectiveness of inorganic fertilizers applied during the summer months in tea plantations could only be 2–4 weeks. The use of biochar-based organic fertilizers can enhance this period by enhancing N retention and availability in the soil. Measuring N mineralization potential via aerobic incubations and N exposure using IEM technology effectively elucidated soil N dynamics during summer period.