Annex  A: Changes to methodology impacting previous releases

This section contains quality information for previous Scottish agriculture greenhouse gas emissions and nitrogen use publications. Quality information for the latest publication is available in Changes to methodology. 

Scottish agriculture greenhouse gas emissions and nitrogen use: 2023-24 -  changes to farm-level estimates methodology

Improvements to Agrecalc methodology

Methodology improvements have been made for absolute emissions estimates for 2021-22 and onwards. This means that estimates from 2021-22 are not directly comparable with data from previous years. Previous years have not been revised as not all data are available.

Farm GHG emissions are produced using the Agricultural Resource Efficiency Calculator (Agrecalc). From 2021-22 onwards, estimates were produced using Agrecalc Cloud, whereas earlier estimates were produced using a legacy version of Agrecalc Web. Agrecalc Cloud methodology changes include:

• Updates to models based on IPCC (2019) guidelines
• Using Global Feed LCA Institute (GFLI) database for feed emissions
• Using Fertiliser Europe database for fertiliser emissions
• New manure management and mitigation options

Agrecalc have published more information about changes to the platform.

Methodology changes are expected to result in a shift in absolute emission estimates. Updates to methane conversion factor coefficients and coefficients for manure emissions used in Agrecalc Cloud, compared with those used in Agrecalc Web, have generally impacted farm type emission estimates in the following ways: 

• Agrecalc Cloud estimates for dairy, mixed, Less Favoured Area (LFA) cattle and lowland cattle and sheep farms, are generally smaller than previous Agrecalc Web estimates.
• Agrecalc Cloud estimates for LFA sheep and LFA cattle and sheep farms are generally larger than previous Agrecalc Web estimates

Limitations in data collection under the previous Agrecalc Web methodology may also result in smaller Agrecalc Cloud estimates for some farms, where transferred manure was not captured. Previously, manure spreading was accounted for but not attached to specific crops. Emissions from spreading stayed with the livestock. In Agrecalc Cloud, emissions from manure spreading are explicitly associated with crops. Older data migrated from Agrecalc Web does not map out where manure was spread, meaning it is not currently possible to account for spreading of home-produced manure for these reports.

Agrecalc Cloud estimates for cereals and general cropping farms may be smaller than corresponding Agrecalc Web estimates. This is due to a database change to Fertiliser Europe, where the embedded emissions in fertiliser and lime are expected to be lower than previously reported.      

Improvements to calculation of farm-level averages

Estimates for absolute emissions per hectare, nitrogen balance and NUE in the 2023-24 publication are produced using ReGenesees R package (svystatQ). This is the same package used for the FBS calibrating weighting method, calculating estimates and uncertainty for complex sample surveys. Previously estimates were produced using the Spatstat R package. This may result in very small differences to previously published results. This change aligns our estimates with the methodology used to produce 95% confidence intervals for the results.