Chemical immobilization of heavy metals is a simple, low-cost, and environment-friendly technology for remediation of heavy metals contaminated soils. However, changes in environmental conditions, such as water management, acid deposition, temperature fluctuation, etc., might result in release of metal ions from the fixation sites, and the long-term stability of immobilization remediation is unclear. This study attempted to investigate the impact of water management strategies (wetting-drying cycle and dry cycle) on the stability of heavy metal immobilization by one-time application of biochar during 3 consecutive years of rice-wheat crop in Cu/Cd-contaminated soil. The transformation and accumulation of Cd and Cu in soil-crop system and the morphololgy and composition of biochar were analyzed. The results revealed that wetting-drying cycle and drying treatments reduced the contents of available Cd and Cu in soil by 15.9%–17.7% and 23.9%–31.5% and by 19.8%–62.7% and 16.1%–65.0%, as well as increased soil pH by 0.11–0.31 and 0.17–0.56, respectively. In the wetting-drying cycle treatment, biochar was more favorable for decrease in Cd and Cu accumulation in crop, when compared with that in dry treatment; however, the differences were insignificant in the subsequent years. Although the different water management strategies had no obvious effect on the soil total C, physicochemical analysis of the biochar collected after pot experiments indicated that the obvious structural decomposition of biochar in the drying treatment may have resulted in the release of heavy metals immobilized in biochar. These findings help in better understanding of the long-term immobilization mechanism of biochar in soil-plant system.

化学重金属固定化是一种简单，低成本且环境友好的技术，用于修复被重金属污染的土壤。然而，诸如水管理，酸沉积，温度波动等环境条件的变化可能导致金属离子从固定位点释放，并且固定修复的长期稳定性尚不清楚。本研究试图研究连续3年水稻/小麦作物在Cu / Cd污染土壤中一次性施用生物炭对水分管理策略（干湿循环和干燥循环）对重金属固定化稳定性的影响。 。分析了土壤-作物系统中Cd和Cu的转化积累，生物炭的形态结构和组成。结果表明，干湿循环和干燥处理使土壤中有效Cd和Cu的含量降低了15.9％–17.7％和23.9％–31.5％，以及19.8％–62.7％和16.1％–65.0％，以及使土壤pH值分别增加0.11-0.31和0.17-0.56。在干湿循环处理中，与干处理相比，生物炭更有利于减少作物中Cd和Cu的积累；但是，在随后的几年中，差异并不明显。尽管不同的水管理策略对土壤总碳没有明显影响，但盆栽试验后收集的生物炭的理化分析表明，生物炭在干燥处理中的明显结构分解可能导致固定在生物炭中的重金属的释放。