农田氧化亚氮排放和产量对水氮输入以及气候变化的综合响应

Crop yield, water and nitrogen use efficiency, and nitrous oxide emission in the North China Plain (NCP) are significantly influenced by irrigation, fertilizer applications and climate change/variability. Nitrous oxide emission from soil is controlled by nitrification and denitrification, which determined by soil water content, temperature, and the concentrations of ammonium and nitrate in the soil profiles. These factors are highly related to agricultural practices and climate. The complicate interactions among these processes results in the large uncertainty of quantification in predictions, which greatly limit the understanding of nitrous oxide emission over farm land, and evaluations for the 'Best Management Practices'. This will lead to decrease nitrous oxide emission and maintain high-efficient agricultural output in the North China Plain (NCP) in adaptation to climate change. This project will conduct three years field experiments with two irrigation levels and four fertilizer application levels to reveal crop production, dynamics of soil moisture, temperature, concentrations of nitrate and ammonium over the 0-100cm soil profiles, and nitrous oxide fluxes at the soil surface. The aims are to 1) study the response of nitrous oxide emission to 0-100 cm soil water content, temperature, and concentrations of nitrate and ammonium; and 2) investigate the impacts of irrigation and fertilizer applications on crop yields, water and nitrogen use efficiency, and nitrous oxide emissions; 3) develop one process-based soil carbon and nitrogen module, and incorporate into crop model (APSIM). The model will be calibrated and validated against the field experiments, and then used to analyze the effect of irrigation, fertilizer applications and climate change/variations on nitrous oxide emission, crop yield, and water and nitrogen use efficiency in NCP. The project will also explore optimal agricultural managements, aiming at decreasing nitrous emissions and maintaining the high-efficient agricultural output under climate change/variations.

水氮输入水平和气候变化与波动显著地影响着华北平原的农业生产、农田水分和养分利用效率以及温室气体-氧化亚氮的排放。农田氧化亚氮排放依赖于不同土壤剖面铵态氮和硝态氮浓度分别响应相应的土壤水分、温度，而这一过程又决定于气候条件与水肥管理措施。这些复杂交互作用带来了定量化的不确定性，从而制约了减少农田氧化亚氮排放的最佳农田水氮管理的研究。本项目拟在作物－水分和养分关系实验和农田土壤氧化亚氮通量观测的基础上，1）探讨土壤氧化亚氮排放对土壤剖面的水分、温度以及氨态氮和硝态氮浓度的响应机制；2）分析多个气象要素变化和水氮输入水平对作物产量、水分和养分利用效率以及土壤氧化亚氮排放的综合影响；3）将基于土壤生物化学过程为土壤机理模型引入农业系统模型，检验和验证该农业系统模型在反映作物生长和土壤碳氮过程对气候变化的响应能力，通过情景分析，探索气候变化/波动背景下，减少土壤氧化亚氮排放的优化农田水氮管理方案。

作为主要温室气体之一的氧化亚氮在大气中的含量自工业革命后迅速增加。农业生态系统是氧化亚氮排放的主要源头之一。箱法和微气象法是当前氧化亚氮排放观测的主要手段。本项目开展了为期两年的农田实验，获取了一套完整的作物生长发育，土壤剖面水分、温度、硝态氮和铵态氮动态以及氧化亚氮排放数据。研究综述了氧化亚氮的模拟和分析了由观测时间和观测频率所导致的日排放的误差，分析了有不同数据来源校正模型所导致的模拟误差，并应用观测数据结合情景分析探索了华北平原最优肥料管理措施。氧化亚氮的模拟机理综述研究表明，土壤氧化亚氮、硝化和反硝化速率对环境响应在不同模型中差异显著。结合当前实验研究，模型可在硝化和反硝化速对反应底物以及温度的响应上给予理论上的提高，未来的研究要集中于不同环境下各个环境因子对氧化亚氮排放的影响。应用微气象法观测的连续氧化亚氮通量揭示了，土壤氧化亚氮排放没有明显的日变化动态，用任意时刻的观测去估算日排放量都会具有巨大的误差，该误差可以通过观测频率的增加而提高。应用不同方法观测的氧化亚氮通量数据校正后的模型可以准确的模拟来自不同观测方法观测的排放通量，但是应用不同观测方法校正的模型去预测不同施肥条件的排放通量时会导致40-60% 的差异。APSIM模型能够很好的模拟作物产量、生物量以及土壤氧化亚氮排放，通过长期的模拟分析表明，在华北平原，施肥量由当前的390kg N/ha降低到330kg N/ha并不会显著的降低产量但是可以显著的降低氧化亚氮排放。