紫色土坡地农田活性氮气体交换与氮流失协同过程与通量研究

Sloping croplands of purple soil, distributed widely in the upper reaches of Yangtze River, play an important role for agriculture in sothwestern China. A large amount of nitrogen loss from hillslope cropland in the purple soil areas due to low utilization efficiency of fertilizer and heavy soil and water erosion, thus, pose a severe threat to the atmospheric environment and the water quality of the Yangtze River.So, it is an inevitable choice to cut down the emssion of reactive gaseous nitrogen and diffuse nitrogen simultaneously. However, the mechanisms and fluxes of the reactive nitrogen loss via hydrological and gaseous pathways have not been well documented because of isolated study on separate losing pathway. It is crucial important to conduct coupling researches on hydrological and gaseous loss of nitrogen so as to understand mechanisms on manipulation of gaseous and aqueous nitrogen loss jointly. So, we proposed to conduct this coupling research on processes and fluxes of nitrogen loss via hydrological and gaseous pathways in sloping cropland of purple soil. In this proposal, synchronous monitoring on processes of reactive gaseous nitrogen (N2O, NO and NH3) emission along with diffuse nitrogen loss will be conducted in the free-drain lysimeters of purple soil. Emission rate of N2O and NO will be determined by Static chamber-Gas chromatograph and NOx detector. Ammonia volatilization will be measured by DTM (Dr?ger-Tube Method) techanique. Discharge of overland flow, subsurface flow and sediment yield will be monitored and sampled in the hillslope free-drain lysimeters. Concentration of different nitrogen forms in drainage water will be analyzed by automatic flow injection method after digestion. The distribution of nitrogen in the soil-plant-water system will be determined by N-15 tracer technique. Impacts of rainfall intensities, slope gradients and fertilization regimes on both aqueous and gaseous nitrogen loss will be studied by rainfall simulation experiments. Based on fully understanding the coupling mechanisms and processes of reactive nitrogen loss via gaseous and hydrological pathways, a new process-based biogeochemical model with enhanced hydrological function will be developed by incorporating hydrological process equations into biogeochemical model as to provide modeling tools for both gaseous nitrogen emission and hydrological nitrogen loss. Then, balance of nitrogen in the sloping cropland of purple soil will be assessed for better management of fertilizer nitrogen. Therefore, basic scientific supports will be provided for both sustainable agriculture and environmental protection.

紫色土坡地氮肥投入高，利用率低，损失量大，造成突出的大气和水环境污染问题，大气活性氮污染物与氮流失的协同管控成为环境保护的必然选择。但以往的农田活性氮气体排放与氮流失过程研究相对孤立，氮素气体交换和氮流失的协同过程与关联机制不清楚，导致农田活性氮气体减排与氮流失控制顾此失彼。针对上述问题，利用紫色土坡地lysimeter装置，结合N-15示踪技术和人工模拟降雨试验，开展紫色土坡地氮流失与活性氮气体交换过程的同步观测，研究坡地活性氮气体交换与氮流失的协同过程、通量及其影响因素，查明活性氮气体交换与氮流失的关联机制和通量消涨关系，阐明坡地氮素土-气交换与土-水迁移的协同机制和径流驱动机理，揭示氮流失主导的坡地氮素循环规律，建立兼顾氮素溶质迁移与气体交换的藕合模型，模拟紫色土坡地不同氮肥管理下的活性氮气体排放和径流、泥沙迁移的氮通量，为紫色土坡地农田氮素管理和环境保护提供科学依据。

针对我国坡耕地氮素流失途径与通量研究的不足，该基金通过野外定位观测并结合15N示踪技术对四川盆地紫色土坡耕地氮素径流、气态流失途径与通量及氮平衡状况开展了系统和深入的研究。结果发现：（1）硝酸盐淋失是紫色土坡耕地氮素流失的主要途径，虽主要发生在雨季但约占全年施氮量的20%，是我国农田硝酸盐淋失的热点地区，可能对长江流域水环境的水体氮负荷造成重大压力；（2）紫色土坡耕地小麦-玉米轮作体系氧化亚氮排放通量与系数远低于华北平原小麦-玉米轮作体系，并且发现硝酸盐淋失与氧化亚氮排放之间存在“trade-off”的关系；（3）发现硝酸盐淋失和氨挥发是紫色土坡耕地小麦-玉米轮作体系的主要水文与气态损失途径，以有机肥替代部分无机氮肥可保持作物产量、减少环境氮流失，并阐明施用有机肥可“重建”农田土壤碳氮耦联效应；（4）提出了yield -scaled NO3- leaching指标（kg N Mg-1 grain yield）来评价硝酸盐淋失，并基于全球已有数据证明该指标是可持续集约化农业框架下农田硝酸盐淋失的有效评价指标；应用该指标对紫色土坡耕地四种不同施肥措施下的硝酸盐淋失进行评价，发现有机-无机肥配施是该地区坡耕地农田生态系统基于环境影响和产量两方面的最佳施肥方式。（5）在国际广泛应用的生物地球化学DNDC模型基础上，引入土壤通用流失方程，并借鉴SWAT模型中SCS方程，嵌入DNDC模型，修改DNDC模型结构，构建了具有水文过程耦合的Hydro-DNDC模型，实现了生物地球化学与面源污染过程协同模拟功能。该项目发表论文12篇，SCI论文5篇。

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