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

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.