Scottish Nitrogen Balance Sheet, 2021

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:

Detailed import/export statistics for volumes of goods and materials can generally only be obtained at the UK level, and not enough detail is currently available to extract data for Scotland from the few data sources that do exist (e.g. summary HMRC statistics, Input-Output tables). Partial import/export data are available or can be reasonably inferred, but only for some specific sub-sectors of the economy (e.g. data exists on roundwood exported from Scottish forestry, or any use of soya as animal feed in Scotland can be assumed to be imported). The Scottish Material Flow Accounts also attempt to derive some flows of materials and produce from the available statistics, but there remain significant data gaps.

In addition to these trade flows, 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.

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.