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Two virtual joint centers for nitrogen agronomy were established between the UK and China to facilitate collaborative research aimed at improving nitrogen use efficiency (NUE) in agricultural production systems and reducing losses of reactive N to the environment. Major focus areas were improving fertilizer NUE, use of livestock manures, soil health, and policy development and knowledge exchange. Improvements to fertilizer NUE included attention to application rate in the context of yield potential and economic considerations and the potential of improved practices including enhanced efficiency fertilizers, plastic film mulching and cropping design. Improved utilization of livestock manures requires knowledge of the available nutrient content, appropriate manure processing technologies and integrated nutrient management practices. Soil carbon, acidification and biodiversity were considered as important aspects of soil health. Both centers identified a range of potential actions that could be taken to improve N management, and the research conducted has highlighted the importance of developing a systems-level approach to assessing improvement in the overall efficiency of N management and avoiding unintended secondary effects from individual interventions. Within this context, the management of fertilizer emissions and livestock manure at the farm and regional scales appear to be particularly important targets for mitigation.

The International Union for the Conservation of Nature (IUCN) defines nature-based solutions (NBS) as “actions to protect, sustainably manage, and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits”. We assessed evidence for the greenhouse gas (GHG) mitigation potential of four nature-based solutions in Scotland (agroforestry, hedgerows, un-cultivated riparian buffer zones and the restoration of species-rich grasslands) and how these can help mitigate the impacts of climate change and reduce biodiversity loss. In addition, we provided a synthesis of the strength of evidence for including these as part of Net Zero policy objectives and carbon codes.

Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (N$_{2}$O). Previous meta-analyses have linked various biochemical properties of crop residues to N$_{2}$O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N$_{2}$O emissions from specific residues. Here we combine comprehensive databases for N$_{2}$O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N$_{2}$O emissions. On average, crop residue incorporation increased soil N$_{2}$O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N$_{2}$O emissions. Crop residue effects on N$_{2}$O emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N$_{2}$O emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N$_{2}$O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated N$_{2}$O emissions, whereas mature residues with opposite characteristics had marginal effects on N$_{2}$O. The most important crop types belonging to the immature residue group ��� cover crops, grasslands and vegetables ��� are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high N$_{2}$O emissions.

Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to ad- dress the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emis- sions of the greenhouse gas nitrous oxide (N2O) from soils. A better understanding of how to mitigate N2O emissions due to crop residue management while promoting positive effects on soil carbon is needed to reconcile the opposing effects of crop residues on the greenhouse gas balance of agroecosystems. Here, we combine a literature review and a meta-analysis to identify and assess measures for mitigating N2O emissions due to crop residue applica- tion to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation ofresidues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N2O emissions. Other practices such as incorporation timing and interac- tions with fertilisers are less conclusive. Several of the evaluated N2O mitigation measures implied negative side- effects on yield, soil organic carbon storage, nitrate leaching and/or ammonia volatilization. We identified additional strategies with potential to reduce crop residue N2O emissions without strong negative side-effects, which require fur- ther research. These are: a) treatment ofcrop residues before field application, e.g., conversion ofresidues into biochar or anaerobic digestate, b) co-application with nitrification inhibitors or N-immobilizing materials such as compost with a high C:N ratio, paper waste or sawdust, and c) use ofresidues obtained from crop mixtures. Our study provides a scientific basis to be developed over the coming years on how to increase the sustainability of agroecosystems though adequate crop residue management.

This thesis presents the analysis and design of high-efficiency battery chargers for heavy duty EV applications. The rise in popularity of the electric vehicles (EVs) due to their increased efficiency over conventional internal combustion engines, has driven the need for more battery charging infrastructure. Furthermore, heavy duty vehicles are also being converted to electric to fill needs such as public transportation via bus fleets as well as cargo delivery via semi-trucks. Such heavy duty vehicles require more energy than personal transportation vehicles and thus require larger battery packs. To charge heavy duty battery packs in the same amount of time as the typical EV, higher power chargers are required. Energy is distributed through the grid network, and a battery charger is converts the grid power into a regulated output for battery charging. The novel battery charging designs investigated in this thesis are classified differently than traditional designs because they have fewer switching stages to convert the power. The unique approach taken allows these designs to have higher efficiency overall than a traditional battery charger design. The new converter designs are refereed to as the three-level (3L) asymmetrical full bridge (3LAFB) and 3L asymmetrical dual active bridge (3LADAB). The operation of each converter is briefly discussed to help develop context for the hardware and controller designs. The controller design for the 3LAFB topology is developed to explain the control objectives of the 3-port dc-dc converter. Hardware results prototype designs are presented to validate proposed chargers and controller designs. A high power extreme fast charger (XFC) structure is proposed using multiple lower power modules. The high-efficiency design of a single module is presented and hardware results are given.

This project set out to review the current state of knowledge on the potential for carbon sequestration in key Scottish upland open habitats. Upland soils play a vital role in regulating greenhouse gas (GHG) emissions in our environment. Scotland’s soils contain 2500-3500 Mt of carbon, much of which is located in upland soil environments. This quantity of carbon is the equivalent of more than 200 years of annual emissions of greenhouse gases from the whole Scottish economy. To achieve Scotland’s ambitious net-zero emissions targets, sound management of uplands and their soils will thus be critical. Despite the potential of soils to store carbon, however, there is uncertainty as to the long-term stability of this carbon pool. Increasing temperatures, altered patterns of rainfall distribution and changes in land use threaten to reduce soil carbon stocks. This review identifies the key drivers of change such as: climate change; nitrogen deposition; changes in atmospheric carbon dioxide concentrations; and local land management factors such as grazing by sheep and deer, and burning to maintain habitat and vegetation quality for grazing animals and grouse. It covers three upland habitats: upland dry heath, upland wet heath and upland grasslands, defined by vegetation communities. It assesses potential greenhouse gas (GHG) fluxes and the impact on biodiversity within these habitats.