多孔硅藻土负载尿素和双氰胺对提高氮肥长效利用率及其机制研究

The low use efficiency of nitrogen (N) fertilizer not only causes great waste of resources, but also triggers environmental pollution. Nitrification inhibitors can improve the use efficiency of N fertilizer and lower the environmental pollution caused by N fertilization, among which dicyandiamide (DCD) is one of the most commonly used inhibitors, but easy to lose with water and degrade. In order to enhance the persistence of DCD in soil, the project intends to load DCD and urea simultaneously into the pores of the environment-friendly micro/nano porous diatomite, with the slow release principle of substances in the pores of micro/nano porous material, to achieve the slow release of N fertilizer and the prolongation of nitrification inhibition, aiming at increasing the N fertilizer use efficiency and reducing environmental pollution. In addition, the surface of diatomite is negatively charged, which can absorb ammonium (NH4+) in the soil, further resulting in the reduction of N fertilizer waste and environmental pollution caused by ammonia volatilization. To meet these goals, the research contents of this project include: first, modifying the surface of the natural mineral diatomite to obtain the diatomite with a micro/nano porous structure; second, exploring the inhibitory effects of the mixing ratio of urea and DCD and their load on the nitrification; finally, revealing the mechanism of the nitrification in agricultural soil regulated by the micro/nano porous diatomite loaded with urea and DCD together, to in situ achieve “slow release, nitrification inhibition and the effective immobilization of NH4+”, thus decreasing N loss and environmental contamination. Results of this investigation will have important theoretical and practical significance for the enhanced use efficiency of N fertilizer in agricultural soils and ecological environment protection.

氮肥利用率低会造成资源浪费和环境污染。硝化抑制剂能够提高氮肥的利用率和减少氮素污染，其中双氰胺是最常用的一种抑制剂，但易随水流失和降解。为了提高双氰胺在土壤中的持久性，本项目拟利用微/纳米多孔材料对孔中物质的缓慢释放原理，将双氰胺和尿素同时负载到环境友好的微/纳米多孔硅藻土的孔中，实现对氮肥的缓效释放和延长硝化抑制效果，达到提高氮肥利用率、减少环境污染的目的。另外，硅藻土表面带负电荷，可吸附土壤中的铵，也能减少氨挥发造成的氮肥浪费和环境污染。为此，首先对天然矿物硅藻土进行表面修饰与改性，获得具有微/纳米多孔结构的硅藻土；探索尿素和双氰胺的混合比例以及负载量对硝化作用的抑制效果；揭示尿素和双氰胺同时负载的微/纳米多孔硅藻土对土壤硝化作用的调控机制，同时实现“缓效释放、硝化抑制和铵的有效固定”，减少氮素的损失和环境污染。该项目对农田土壤氮素的高效利用和生态环境保护，具有重要的理论和实际意义。

氮肥利用率低会造成资源浪费和环境污染。硝化抑制剂能够提高氮肥的利用率和减少氮素污染，其中双氰胺是最常用的一种抑制剂，但易随水流失和降解。因此，亟需提高双氰胺在土壤中的持久性。为此，本研究借助纳米材料合成和表征技术，合成了不同尺寸和孔径的SiO2材料并对天然硅藻土进行改性；研究了海胆状空心硅球对DCD和NH4Cl的负载情况以及海胆状空心硅球同时负载满DCD和NH4Cl的释放效果，制备了负载不同比例氮和DCD的海胆状空心硅肥；利用室内模拟试验，探究了负载不同比例氮和DCD的海胆状空心硅肥对农田土壤硝化作用的抑制效果及作用机理。结果发现：海胆状空心硅球对氮肥吸附效果较好，最大负载量达到160 mg g-1，海胆状空心硅对DCD最大负载量高达250 mg g-1；负载满氯化铵和DCD的海胆状空心硅中NH4+-N和DCD的最大释放量分别达到38 mg g-1和112 mg g-1；在此基础上，制备了负载不同比例氮和DCD的海胆状空心硅肥，其中N:DCD的比例依次为1:0、1:1、1:5和1:10。负载不同比例氮和DCD的海胆状空心硅肥在培养后前3 d内其下降幅度显著低于NH4Cl处理；NH4+-N 浓度随着DCD比例的增加而显著增加，其中1:5处理中负载的DCD对土壤中氨氧化细菌具有很好的抑制效果。DCD通过抑制氨氧化过程避免NO2--N累积，减少硝化细菌反硝化的底物，从而减少N2O排放同时避免高浓度NO2--N产生的毒害作用。综上分析，海胆状空心硅可以同时负载NH4Cl和DCD，而且能够延缓NH4+在土壤中的释放速率，缓慢释放DCD，抑制土壤硝化过程，从而延长铵态氮肥和DCD在农田土壤中持久性，提高氮肥的利用效率。研究结果对农田土壤氮素的高效利用和生态环境保护，具有重要的理论和实际意义。