lnfluence of historical management and soil moisture on N2O emissions from grasslands Programme of Work

一氧化二氮(N2O)是一种强大的温室气体，也是平流层中主要的臭氧消耗物质。它主要由微生物活动产生，其中45%来自农业(Syakila，2011)。微生物的活动受到土壤水分、营养状况和许多其他物理化学过程的影响。已经观察到，施肥前的土壤条件会影响微生物的活动，特别是土壤水分和养分状况。后者受到土壤历史管理的影响，特别是耕作、使用无机肥料和有机肥以及作物特性。目前对排放及其控制因素的了解取决于与排放同时发生的条件或最近发生的事件的结果。我们提出了土壤历史水分(周-月)和管理(年-十年)影响微生物对化肥的响应。本项目将研究土壤前水分和历史氮素管理对N2O排放及其减少的产物N_2的影响，以对比不同环境条件下的土壤类型，以及这种影响与反硝化微生物活性和基因表达的关系。最终目标是了解减少N2O排放的过程及其对农业实践的影响。该项目将包括实验室、蒸渗仪和田间规模的实验。N2O和N2的排放将使用气相色谱进行，并与微生物群落结构和反硝化基因表达相关，包括最近发现的一氧化二氮还原酶第二指南(Jones，2014)。将通过破坏性采样和提取不稳定的氮和碳化合物以及直接测量土壤水化学来评估土壤化学。第一步：土壤表层水分对氮素循环的影响。将选择不同土壤类型的对比纹理。将进行实验室培养，以研究不同土壤水分强度和持续时间对氮肥和碳肥施用前N2O排放和N2O/N2比值的影响。还将设置蒸渗仪，以评估在较高土壤水分水平下的淋洗损失，以及通过破坏性采样土壤养分浓度和微生物种群的变化。第二步，历史土壤投入管理对氮素循环的影响。与第一步类似，将使用培养和蒸渗仪来研究以前的管理(N和C的使用以及硝化抑制剂的使用)对N2O/N2比率和土壤养分(特别是与碳质的交互作用)和微生物种群的影响。我们还将包括哈彭登长期的草地和农田试验的土壤，这些土壤已经接受了无机和有机材料以及石灰的定期应用，以评估这种效果。步骤3.探索大型数据集。利用北威克农场平台的现有数据，我们将探索土壤水分对N循环、淋溶和径流以及N2O排放的长期影响。学生还将访问英国温室气体平台N2O排放和元数据档案，以探索不同地理气候区一系列N投入的降雨量、土壤湿度和N2O排放之间的相互作用。将利用这些数据对机械模型进行验证，并进一步用于模拟情景，以预测不同条件下N的损失。统计模型将被用来建立经验关系，为前者提供信息。

Nitrous oxide (N2O) is a powerful greenhouse gas and the dominant ozone-depleting substance in the stratosphere. It is predominantly produced by microbial activity, 45% of which is from agriculture (Syakila, 2011). Microbial activity is influenced by soil moisture, nutrient status and many other physico-chemical processes. It has been observed that soil conditions prior to fertiliser application can impact microbial activity particularly soil moisture and nutrient status. The latter is affected by the historical management of soil, particularly cultivation, application of inorganic vs organic fertiliser and crop characteristics.Current knowledge of emissions and their controlling factors rely on conditions occurring simultaneously with the emissions or as a result of recent events. We propose that historical soil moisture (weeks-months) and management (years-decades) influence microbial response to fertiliser application.This project will investigate the effect of pre-soil moisture and historical nitrogen management on N2O emissions and the product of its reduction, N2, for contrasting soil types under different environmental conditions and how this correlates to denitrifier microbial activity and gene expression. The ultimate goal is to understand the processes by which N2O emission can be reduced and influencing agricultural practices to this end.This project will comprise laboratory, lysimeter and field scale experiments. Emissions of N2O and N2 will be carried out using gas chromatography and correlated to microbial community structure and denitrification gene expression including the recently discovered second guide of nitrous oxide reductase (Jones, 2014). Soil chemistry will be assessed via destructive sampling and extraction of labile nitrogen and carbon compounds, as well as direct measurement of soil water chemistry. Step 1. Effect of pre-soil moisture on N cycling. Different soil types of contrasting textures will be selected. Laboratory incubations will be carried out to investigate the effect of different soil moisture intensities and duration prior to N and C application on N2O emissions and the ratio N2O/N2. Lysimeters will be setup to also assess losses via leaching at the higher soil moisture levels and changes in soil nutrient concentration and microbial populations via destructive sampling. Step 2. Effect of historical soil input management on N cycling. Similarly to Step 1, incubations and lysimeters will be used to investigate the effect of previous management (N and C application and use of nitrification inhibitors) on the N2O/N2 ratios and soil nutrients (particularly interaction with carbon quality) and microbial populations. We will also include soil from Long Term grass and arable Experiments at Harpenden which have received regular applications of inorganic and organic materials and lime to assess this effect. Step 3. Large datasets exploration. Using existing data from the North Wyke Farm Platform we will explore the long term effect of soil moisture on N cycling, leaching and runoff as well as N2O emissions. The student will also have access to the UK GHG Platform N2O emission and metadata archive, to explore interactions between rainfall, soil moisture and N2O emissions for a range of N inputs in different geoclimatic zones. Mechanistic models will be validated using these data and further used for simulating scenarios to predict losses of N under different conditions. Statistical models will be used to develop empirical relationships to inform the former.