Capturing Cropland and Grassland Management Impacts on Soil Carbon in the UK LULUCF Inventory

This project aimed to identify the extent to which emissions due to changes in Soil Organic Carbon (SOC) stocks arising from Cropland and Grassland/Grazing Land management can be incorporated into the UK’s Land Use, Land Use Change and Forestry (LULUCF) inventory. \n \nKey management activities were identified which might affect SOC stocks. \n \nA literature review carried out as part of the project concluded that tillage reduction cannot be considered a reliable management option to increase the SOC content of UK soils. However increasing crop residue returns and increasing inputs of manure and fertiliser could increase SOC stock although the SOC stock increases resulting from manure and fertiliser inputs could be outweighed by increases nitrous oxide emissions and the risk of nitrate run-off. \n \nThe review found that increasing crop yields through increased fertilisation and improved crop rotation could increase the annual input of crop residues and root exudate to soils and hence increase SOC on low fertility soils. Manure additions resulted in greater C sequestration than the addition of equivalent amounts of N as mineral fertiliser and the effect lasted longer. However, increasing inputs of nitrogen from fertiliser or manure risk increasing N2O emissions which could negate any increases in SOC stock. \n \nIPCC default stock change factors were judged to be inappropriate to the UK, based on expert opinion and the literature review findings. Therefore the project used the Daily DayCent and Landscape DNDC models to attempt to estimate stock change factors for Cropland management activities under UK conditions. Although based on a very limited dataset this suggested that the effect of Cropland management activities under UK conditions might be less than implied by the IPCC stock change factors. Tillage reduction was found to have little effect on SOC stocks. Increasing manure and crop residue inputs increased SOC stocks, with manure inputs being particularly effective. \n \nA framework for reporting SOC stock changes resulting from Cropland management was developed, and used to assess mitigation options. Overall the impact of Cropland Management on SOC is likely to be very small compared to other activities in the LULUCF inventory such as land use change. The most effective mitigation option was using Cropland from annual tillage crops to perennial crops, fallow and set aside. However given the need for food production there is limited scope for such change. Increasing manure, fertiliser and crop residue inputs gave smaller increases in SOC stocks, but practical considerations limit the scope of these actions. \nLack of field data on the effect of Grassland improvement on SOC stocks was identified as a knowledge gap. The literature review suggested that intensification could increase SOC stocks under pasture on mineral soils. However, expert opinion suggested that this might not be the case for rough grazing on organo-mineral soils, where intensification might lead to SOC loss. This lack of data meant that it was not possible to calibrate or validate models to estimate UK specific stock change factors for Grassland. As the IPCC stock change factors were judged to be inappropriate to UK conditions assessment of the mitigation potential of Grassland management using these factors was not carried out to avoid presenting potentially misleading results. Suggested strategies for filling these knowledge gaps are outlined in the report. \n \nAttempts to assess grass/crop rotation patterns across the UK using data from the Integrated Administration and Control System (IACS) used to handle Common Agricultural Policy (CAP) payments were hampered by difficulties in obtaining access to the data. However land use change matrices were generated for England and Wales, and used to map areas of change. Subject to data availability, this approach could be used in future inventories to give a better representation the effect of rotation patterns on SOC stocks. \n