农田中氮素无效损失和重金属污染问题并存，兼顾土壤中氮持留和重金属固定，对于减少营养盐损失、控制面源污染、降低土壤重金属污染风险具有重大意义。本研究在农田中氮素和重金属赋存状态评估基础上，提出通过生物炭复合材料强化农田氮持留和重金属固定的技术方案。研究制备出多种生物炭复合材料，评估了其对氮素和重金属的吸附解吸性能并建立了吸附机理，通过降雨模拟和植物实验，分析了其对氮素和重金属迁移转化的影响规律，从而构建了生物炭复合材料改善土壤氮循环和强化重金属固定的物化-生化耦合机制。农田中的NH4+?N和NO3-?N同时大量存在，这与广泛分布的氮循环微生物有关。氮肥施加等农业活动是土壤中重金属有效性提升的重要因素，贡献率超过了50%；同时，重金属有效性提升又可能促进土壤氮物质循环，不利于氮肥使用管理。

Nitrogen loss and heavy metal pollution in farmland usually coexist and interact with each other, and few studies have focused on this topic to our best knowledge. Based on the analysis of occurrence of nitrogen and heavy metals in farmland, modified biochar technique was proposed for simultaneous nitrogen retention and heavy metal immobilization. In this study, several biochar composites were synthesized to simultaneously and efficiently adsorb nitrogen and heavy metals. Based on the adsorption-desorption, stimulated rainfall, and rice cultivation experiments, the mechanisms coupling physical adsorption and biological effcet were summarized finally.Both NH4+?N and NO3-?N largely existed in farmland, mainly attributed to the widespread nitrogen cycle microorganisms. The contents of reactive heavy metals have obviously increased in farmland, mainly attributed to agricultural production (such as nitrogen fertilizer application) with contribution of >50%. Moreover, the increase of reactive heavy metals possibly promoted the circulation of soil nitrogen, which is bad for nitrogen fertilizer application.