秸秆还田-水肥一体化模式下农田氮素演化机制

Straw returning to field can increase soil fertility, reduce fertilizer application and environmental pollution, which is in line with the development direction of ecological agriculture. The current study focused on the effects of straw returning to field on the transformation of nitrogen under general management of water and fertilizer, however, the mechanism of soil nitrogen evolution under the mode of fertigation is not clear, which has become the key factor restricting to high efficient utilization of straw returning to field. In this study, winter wheat and summer maize would be chosen as the typical crops, through the in-situ monitoring, to clarify the characteristics of occurrence and content of nitrogen in the soil under the coupling effect of straw returning to field coupling with fertigation in different seasons and different growth periods of the typical crops; at the same time, the evolution law of soil DOM under the coupling effect of straw returning to field and fertigation would be studied using three-dimensional fluorescence technology, through the analysis of soil dissolved organic matter (DOM) composition and dynamic change; finally, on the one hand, a degradation test would be carried out by adding cellulase, to analyze the contents and dynamic changes of nitrogen from the decomposition of straw group to estimate the contribution of nitrogen on the input into the soil from straw decomposition, on the other hand, the exogenous DOM component would be successively added into the undisturbed soil collected from the farmland, by using 15N isotope tracer technique and electron transfer theory, to study the role of DOM components in the nitrification and denitrification from the viewpoint of electron level. Then, combination of the above two aspects to clarify the mechanism of the dynamic evolution of nitrogen under the coupling effect of straw returning to field and fertigation.

秸秆还田能够增加土壤肥力、减少化肥施用和环境污染，符合生态农业发展方向。目前的研究主要集中于秸秆还田在常规水肥管理下氮转化的机制，对于水肥一体化这种水肥耦合模式下土壤氮素演化的作用机制尚不清楚，成为制约水肥一体化模式下秸秆还田高效利用的关键。本研究以冬小麦-夏玉米为对象，通过场地原位监测，明确秸秆还田-水肥一体化模式不同生长季和生育期土壤氮素含量与构成动态特征；同时，采用三维荧光技术，解析土壤中溶解性有机物（DOM）的组成和动态变化，揭示秸秆还田-水肥一体化下土壤DOM的演变规律；最后，一方面，通过添加纤维素酶等开展降解试验，测定秸秆腐解过程氮素含量，估算秸秆腐解对土壤氮输入的贡献，另一方面，采集农田原状土样，添加外源DOM组分，利用同位素示踪技术和电子转移理论，从电子水平定量揭示DOM组分在硝化、反硝化中的作用，综合上述两方面，厘清秸秆还田-水肥一体化模式下氮素动态演变的作用机制。

水肥一体化和秸秆还田是当前节水农业、农业机械化、生态农业发展的重要方向，在水肥一体化和秸秆还田联合作用下，土壤氮素演变呈现与以往传统农业灌溉和种植管理有别的新特征，对该过程土壤氮素演化趋势以及影响机制有待进行阐明。在资助期内，按照既定目标开展了秸秆还田-水肥一体化条件下农田土壤氮素的动态演变、农田DOM及组分变化、秸秆腐解过程中氮转化及电子转移数量等的研究工作。主要取得以下成果：通过田间定位观测，秸秆还田和秸秆配施有机肥处理土壤铵态氮和硝态氮含量逐渐增加，在同等灌水量条件下，秸秆配施有机肥处理土壤的铵态氮和硝态氮含量始终高于秸秆还田处理和对照组，增加灌水促进秸秆释放土壤铵态氮、硝态氮；施加秸秆或配施有机肥，农田DOM含量及类蛋白质和类腐殖酸的积累均呈上升趋势，灌水促进了腐殖化进程；0～60 d为秸秆快速腐解期，60～91 d为秸秆缓慢腐解期，灌水加速秸秆腐解，秸秆中碳、氮释放特征与秸秆累积质量损失率相似，水分对碳、氮的释放影响要高于外源性有机物类型的影响；15N示踪表明，添加秸秆和秸秆配施腐殖酸能提高土壤固铵作用，有利于土壤的硝化作用；土壤中DOM的EAC约是EDC的10倍，说明土壤DOM主要以氧化态形式存在，电子转移能力主要由EAC决定，秸秆配施有机肥处理和秸秆还田处理土壤DOM的ETC呈逐渐上升的趋势，增加灌水有效提高ETC的增幅效果；DOM的HIX值、荧光组分、电子转移能力与铵态氮、硝态氮呈显著或极显著正相关，可见水分调控下秸秆配施有机肥是通过提高土壤DOM含量、腐殖化程度以及电子转移能力，进而提高土壤铵态氮、硝态氮含量。本研究对如何进行土壤氮素调控以提高土壤养分有效性提供了理论支持，对未来农田养分保育和生态可持续提供一定的支撑。项目资助待发表SCIE、EI收录论文1篇，获得省部级科技奖励2项，培养硕士研究生1名。项目投入经费31.6万元，支出23.8219万元，剩余经费用于本项目研究后续支出。