Scottish Nitrogen Balance Sheet 2022

There are two main areas for improvement in the SNBS. The first area relates to consistency by identifying replacements or proxies for some data sources which lack annual updates. The second direction relates to completeness; filling in the remaining data gaps in the SNBS which are currently not estimated.

Summary of current data gaps for the SNBS

The main remaining data gaps in the SNBS can be summarised as follows:

There are some natural processes in terrestrial (and aquatic) ecosystems where nitrogen is taken up and recycled, such as through the decomposition of vegetation, and these are also not quantified here. These processes, which occur across all types of vegetation, woodlands, heathlands, etc. are distinct from those described for forestry operations and the other specific semi-natural area cases covered, where data does exist. These processes are acknowledged as difficult to quantify in the UN ECE guidance and the scientific knowledge the guidance draws on, and data are not required for any of the NUE calculations set out in this report.

There is also currently very limited knowledge on the extent of clover on Scotland’s pastures, and no specific data exist to our knowledge. If this could be improved, it would assist with the quantification of the biological nitrogen fixation for agriculture in the SNBS.

There are gaps remaining concerning the manufacture, consumption and trade in consumer goods. Many manufactured products such as clothing, furniture and electronic equipment is made from materiel which contains Nitrogen; some examples of such materiel are both natural and synthetic fibres contain Nitrogen, wood as seen from the Forestry pool contains Nitrogen and many plastics contain Nitrogen.

In terms of scope for improving the secondary calculation methods (rather than the underpinning data or main economy-wide NUE calculation methods), there are several potential areas for future improvement:

• Agriculture livestock feed conversion calculations: The calculations applied are based on work by SRUC and its representation in Scotland’s Material Flow Accounts (MFA) . It would be preferable to develop these into more comprehensive approaches, should further relevant data (e.g. around the nitrogen content of the wide range of grassland types in Scotland and how these feed into the different livestock sectors) become available in the future.
• Aquaculture livestock feed conversion calculations: The estimates of feed conversion and losses are based on the current modelling used by SEPA for regulatory purposes. However, SEPA recently started a review of their evidence base, and any outcomes should be incorporated into the relevant SNBS calculations once the review has been completed.