橡胶林土壤硝态氮的产生与淋失机制

How to control nitrogen loss and reduce the pressure on environment brought from it has become a major issue in global perspective. The nitrate leaching is an important pathway of nitrogen loss, and it is also the resource for groundwater pollution. Though experiencing long term research, the mechanisms of nitrate leaching under the coupling effect of water and nitrogen still remain unsettled. The theory systematically describing the whole process from the nitrate production to its leaching is especially in lack. Therefore, further understanding the fertilization and irrigation rate is the important cutting point for the research on nitrate leaching. And the systematic analysis process from the nitrate production and its leaching under different precipitation within varieties of ecosystems is the important supplement for improving the leaching mechanism. Our studies showed that in the fertilizing region of rubber plantation, the soil inorganic nitrogen mainly existed in the form of nitrate. And nitrate leaching probably is the important nitrogen loss pathway in rubber plantation soil. Under the condition of the tropical monsoon climate characterized by the obvious alternation of dry and wet weather, the nitrate leaching mechanism might include its surplus accumulation in the dry season and leaching in the rainy season. In this project, the plot experiment and laboratory incubation method are used as tools to employ the systematic research on the process of the production, accumulation, movement and leaching of nitrate in rubber plantation soil for exploring the scientific mechanism from production to leaching of it. It is expected to help developing the fundamental research on the nitrogen loss in rubber plantation soil and in the application supply the scientific evidence for optimizing the nitrogen management of rubber plantation from our work.

减少氮素损失及其对环境的压力，已经成为一个全球性的重大研究课题。硝态氮淋失是氮素损失去向的重要途径，同时也是引起地下水硝酸盐污染的重要原因。长期以来，水氮协同作用下的硝态氮淋失机制尚未完全明确，尤其是缺乏系统的阐述硝态氮从产生到淋失的过程机制。因此，深入理解施氮量与供水量是研究硝态氮淋失的重要切入点，系统分析特定降水条件和不同生态系统的硝态氮从产生到淋洗过程是完善淋失机制的重要补充。我们的研究表明，橡胶林培肥区土壤无机氮主要以硝态氮形式存在，硝态氮淋失可能是其氮素损失的主要途径。在有明显干湿交替的热带季风气候条件下，橡胶林土壤硝态氮可能存在旱季累积与雨季淋失的机制。本项目采用大田试验和室内培养研究手段，对橡胶林土壤硝态氮的产生、累积、移动和淋失过程等进行系统研究，探索硝态氮从产生到淋失的科学机制，期望能促进橡胶林氮素损失去向的基础研究，应用上可以为橡胶林优化施氮管理提供科学依据。

减少氮素损失及其对环境的压力，已经成为一个全球性的重大研究课题。硝态氮淋失是氮素损失去向的重要途径，同时也是引起地下水硝酸盐污染的重要原因。长期以来，水氮协同作用下的硝态氮淋失机制尚未完全明确，尤其是缺乏系统地阐述硝态氮从产生到淋失的过程机制。因此，深入理解施氮量与供水量是研究硝态氮淋失的重要切入点，系统分析特定降水条件和不同生态系统的硝态氮从产生到淋洗过程是完善淋失机制的重要补充。项目采用气压分离（BaPS）技术，研究了酸性砖红壤的总硝化速率和反硝化速率对温度、水分及碳氮源的响应，揭示了在强酸性、寡营养（低碳、低氮）的砖红壤中，土壤有效氮的形态和数量能够显著影响土壤硝化和反硝化过程。但碳源的缺乏是限制橡胶林酸性砖红壤土壤硝化和反硝化过程的主要因素。采用土壤剖面采样法、土壤溶液抽提和土壤水分通量技术，研究了不同施氮水平下橡胶林土壤硝态氮的累积变化和淋洗损失，明确提出了热带季风气候条件下橡胶林土壤硝态氮的淋洗损失具有旱季累积和雨季淋失的规律。采用通气法，研究了橡胶林氮肥表施的氨挥发特征，揭示其氨挥发损失具有旱季损失高、雨季损失低的特点。采用渗漏盘法，田间原位研究了橡胶林氮肥穴施条件下的氮素淋洗损失，发现橡胶林氮肥穴施后，不仅发生了硝态氮的淋失，同时也存在一定量的铵态氮淋洗损失。研究初步确定了橡胶林氮肥穴施后的淋失通量。采用15N示踪技术和土壤剖面采样法，研究了肥料氮在土壤中残留、累积和移动。热带季风气候条件下的橡胶林，氮肥表施后当年残留率23.36%-31.85%，2年后残留率仅10.45%-20.45%。硝态氮在土壤中的累积与施氮量呈显著正相关关系，而硝态氮在土壤剖面中的移动具有一定的偶然性。研究结果有助于阐明橡胶林土壤硝态氮从产生到淋失的机制过程，为揭示橡胶林生态系统氮素损失去向提供一定的理论基础，为橡胶树氮素优化管理提供科学依据。