Comparative analysis of nitrogen accounting models with particular reference to agriculture

Agriculture accounts for the second largest proportion of greenhouse gas emissions in Scotland, particularly through the use of fertilisers, livestock manures and other organic materials such digestate or compost. One approach that could help to reduce these emissions is the use of nitrogen accounting tools. In this report we compare available nitrogen accounting tools to assess their potential application focusing on Scottish agriculture.

With a focus on input-output models, we evaluate the strengths and weaknesses of different models, their practical potential for application to Scottish farm businesses, and their potential to support policy decisions.

Key Findings

Generally, there are common knowledge gaps across many of the tools assessed. This includes a lack of detailed description for nitrogen parameters such as deposition, gaseous losses (particularly ammonia losses), fixation rates (based on legume type and coverage), content in feed, machinery use and wider. Gaps were also found in evidence for the use of novel technologies on farms, efficiency differences from livestock breeding programmes and how the nitrogen accounting tools link more widely, for example with sectors such as industry, transport, human consumption and waste.
We found that the tools available have been designed for specific (different) purposes that vary in spatial scale and which differ in complexity, both in how easy they are to use and in the details describing nitrogen pathways in agricultural systems.
At the national and regional scale from the identified tools, the model by Vogt and the UK Smart Inventory shows the greatest potential to be developed into a national level policy monitoring tool. On the other hand, Farmscoper and IMAGE would be suitable to explore alternative scenarios in the near and further future, respectively.
The tool evaluation process determined that, of the tools reviewed, PLANET, MANNER-NPK and potentially FarmAC are most suitable for Scottish application for calculating farm-level budgets at this time. However, the OverseerFM tool provides the most holistic coverage of farm level management practices influencing nitrogen inputs, transformations, storage and outputs from a farm.

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