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

一氧化二氮（N2 O）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）。微生物活性受土壤水分、养分状况和许多其他物理化学过程的影响。据观察，施肥前的土壤条件会影响微生物活性，特别是土壤水分和养分状况。后者受历史土壤管理的影响，特别是耕作，无机与有机肥料的应用和作物特性。目前对排放及其控制因素的了解依赖于与排放同时发生的条件或近期事件的结果。我们提出，历史土壤水分（周-月）和管理（年-几十年）影响微生物对施肥的反应。本项目将调查前土壤水分和历史氮管理对N2 O排放量的影响及其减少的产物，N2，用于对比不同环境条件下的土壤类型，以及这与微生物活性和基因表达的关系。最终目标是了解减少N2 O排放的过程，并为此目的影响农业实践。该项目将包括实验室、蒸渗仪和田间规模的实验。N2 O和N2的排放将使用气相色谱法进行，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的第二指南（Jones，2014）。将通过破坏性取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。步骤1.前期土壤水分对氮素循环的影响将选择不同质地的土壤类型。将进行实验室培养，以研究不同的土壤水分强度和持续时间之前，N和C的应用对N2 O排放量和N2 O/N2的比例的影响。还将设置蒸渗仪，以评估在较高土壤湿度水平下通过沥滤造成的损失，以及通过破坏性取样评估土壤养分浓度和微生物种群的变化。步骤2.历史土壤投入管理对氮素循环的影响与第1步类似，将使用培养和蒸渗仪研究先前管理（N和C施用以及硝化抑制剂的使用）对N2 O/N2比率和土壤养分（特别是与碳质量的相互作用）以及微生物种群的影响。我们还将包括来自哈彭登长期草和耕地实验的土壤，这些土壤已定期施用无机和有机材料以及石灰，以评估这种影响。步骤3.大型数据集探索。利用现有的数据从北怀克农场平台，我们将探讨长期影响土壤水分对氮循环，淋溶和径流以及N2 O排放。学生还可以访问英国温室气体平台N2 O排放和元数据档案，以探索降雨，土壤水分和N2 O排放之间的相互作用，在不同的地理气候区的一系列N输入。机制模型将使用这些数据进行验证，并进一步用于模拟情景，以预测不同条件下的氮素损失。将使用统计模型来建立经验关系，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.