Grazing behaviour, urine composition and soil properties are key controls of N2O emission factors in the uplands

The aim of this project is to develop an improved understanding of the spatial and temporal interactions between grazing behaviour, forage selection, urine composition and edaphic conditions and to use the insights garnered to improve the accuracy of nitrous oxide (N2O) emission estimates from contrasting semi-improved and unimproved upland grazed pastures in the UK. This is of major importance because (1) urine patches are a significant source of N2O; ca. 19% of the total N2O losses from agriculture, and (2) N2O losses from upland systems are highly uncertain. Current methods of estimating emissions from urine patches ignore the effect that livestock diet, soil type, soil physico-chemical properties and climate have on N2O fluxes. For example, urine N content varies with protein intake, and the metabolic product in the urine (known to affect N2O production) is affected by what livestock graze. Vegetation in different upland areas varies enormously, with diet selection operating in both systems. Hence it is important to link urine composition to animal movement and diet selection.
Soils in the uplands are dominated by peats and podzols with high carbon content and low pH, influenced by cool, wet climates and topography. These factors will also exert systematic controls on rates of N2O fluxes which are likely to be exacerbated following urine deposition. Moreover, the vegetation in different upland areas influences stocking densities and the consequent potential for urine patch overlap, resulting in disproportionate N2O emissions in areas receiving high N loading rates. Soil in these areas can become compacted due to livestock trampling, reducing air filled pore space, increasing anaerobicity and enhancing conditions for N2O losses via denitrification. It is, therefore, essential to establish the relationships between urine composition (the result of grazing preference), soil type, soil physico-chemical properties (which might be influenced by topographic effects on hydrology) and climate in order to generate improved N2O flux estimates, emission factors and carbon footprints from livestock production.
We will address these knowledge gaps through a combination of:
i) Fine-scale mapping of 'static' factors controlling N2O fluxes, i.e. topography, soil type, vegetation type and soil compaction, using high resolution remotely sensed imaging over contrasting upland areas
ii) Mapping of the 'mobile' factors controlling N2O fluxes, i.e. measuring livestock movement and grazing patterns in these two grassland systems using GPS collars, and observing urination events
iii) Collection of urine from sheep grazing dominant vegetation types and relating the urine composition to dietary preference
iv) Measurement of N2O fluxes following the application of collected urine to soil under typical vegetation types, and calculation of robust urine direct N2O emission factors over a 12 month period
v) Conducting controlled replicated experiments to explore the factors controlling N2O fluxes from soil from contrasting field sites (e.g. changing urine composition, water content and levels of compaction)
vi) Developing a novel model framework to predict the statistics of animal occupancy and to integrate predicted urine emissions with spatial and temporal information of landscape-scale explanatory factors in order to quantify aggregate N2O emissions for upland pastures
Uniquely, we will gain improved understanding of the spatial and temporal interactions between grazing patterns, forage choice, urine composition, soil and climate factors and N2O fluxes in upland systems. Outputs from the project will be compared with IPCC Tier 1 and Tier 2 approaches for estimating N2O emissions from livestock grazing in the UK and provide the basis for robust and scientifically defensible alterations to standard inventory approaches, if required, along with inputs to carbon footprinting and to the spatial targeting of mitigation practices.

The outputs of this research will impact on society and the economy by influencing the:
SCIENTIFIC COMMUNITY: Our research will inform scientists working in several areas of research e.g. livestock behaviour, grazing management, ruminant nutrition, GHG emissions and modelling. The unique synthesis of the information generated by this project bridges the gap between research which focusses on dietary preference, food production and nutrient/energy balances, and research which focusses on quantifying the impact of soil amendments on N2O emissions from soils. It will link dietary preferences to soil function in contrasting grassland upland pastures using monitoring and observation, mapping, field and laboratory based measurements, all synthesised in a spatially explicit model.
The project strengthens existing research links on GHG emissions and mitigation between Bangor and RRes-North Wyke, and initiates a new collaboration with Cranfield and Leicester Universities in highly complementary disciplines. Chadwick represents the UK in the Livestock Research Group of the Global Research Alliance on Agricultural GHGs. He also leads the UK GHG Platform project to Improve the Agricultural Greenhouse Gas Inventory for Nitrous oxide (http://www.ghgplatform.org.uk/). Cardenas is responsible for the collation and submission of the UK Agriculture GHG inventory. She is also part of the consortium project to deliver the new Tier 2 GHG inventory for agriculture. Perotto-Baldivieso has worked with GPS collars and spatial analysis in the Caribbean and the United States. He has been the president of the International Affairs Committee for the Society for Range Management (2008-2009). We will raise awareness of this project through these networks, and demonstrate the importance of moving to a more sophisticated approach to reflect the effect of dietary preference on direct N2O emissions.
Participation at International conferences will help communicate results and generate interest for future work. The Nitrogen Workshop (in2016/7) attracts researchers mostly from Europe on all aspects of nitrogen cycling, whilst the International Greenhouse Gases and Animal Agriculture Conference in Melbourne (2016) represent a tremendous opportunity to discuss initial research findings and project goals with researchers from outside Europe.
POLICY COMMUNITY: Results from monitoring of livestock movement at the field and landscape scale, offers the opportunity to explore where targeted mitigation strategies could be cost-effective, e.g. through the use of inhibitors to reduce N2O emissions from hot-spots, or through the frequent moving of feeders. Results could prove N2O emission factors (EFs) from urine to be much lower/larger than the IPCC value due to interactions of urine composition, soil properties and climate, with important policy implications re: improving national inventories.
As part of the GHG Platform, Chadwick and Cardenas are regularly invited to give oral presentations to various audiences; policy makers, farmers and industry, providing opportunities to communicate the findings of this project.
INDUSTRY: Research findings will be communicated to the livestock industry, which has set its own targets for GHG mitigation. Our results will be of interest to them, from an EF point of view, but also in terms of development of mitigation strategies, and in the carbon foot printing of their products for comparison with competing countries, such as New Zealand lamb.
WIDER COMMUNITY: A web page on the Bangor website will provide information on the project and its results. Different aspects of the project will be used for teaching at Bangor, Cranfield and Leicester, generating student projects, and will be presented at annual 'tours' of experiments at RRes-North Wyke and Bangor. We will also feature the project in School Science Week, using visualisation of animal 'movement's to stimulate wider discussion about livestock production and the environment.