Capturing cropland and grassland management impacts on soil carbon in the UK LULUCF inventory

JM Moxley, Steven G.A. Anthony, Khadiza Begum, Anne Bhogal, S Buckingham, Peter Christie, Ulrike Dragosits, Nuala Fitton, Alex Higgins, VM Myrgiotis, Matthias Kuhnert, Scott Laidlaw, Heath Malcolm, RM Rees, Pete Smith, Sam Tomlinson, CFE Topp, John Watterson, J Webb, Jagadeesh Yeluripati

Research output: Book/Report/Policy BriefCommissioned report

Abstract

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. The UK is required to develop such reporting to meet international commitments for reductions in greenhouse gas
emissions.
Developing frameworks for reporting these emissions would also allow assessment of the scope for Cropland and Grassland management to increase SOC stocks as greenhouse gas mitigation measures.
Key management activities were identified which might affect SOC stocks. For Cropland these were
crop type, crop residue returns, manure and fertiliser inputs and tillage regime. For Grassland the
key management activities were Grassland type, residue returns, manure and fertiliser inputs,
rotation pattern and erosion. Drainage of organic soils was not considered in this project.
A 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 in nitrous oxide emissions and the risk of nitrate run-off.
The 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. IPCC default stock change factors were judged to be inappropriate for 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, outputs from the model
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.
A 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 converting Cropland from annual tillage crops to perennial
crops, fallow and set aside. However given the need for food production there is limited scope for
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such change. Increasing manure, fertiliser and crop residue inputs gave smaller increases in SOC
stocks, but practical considerations limit the scope of these actions.
A lack 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.
Attempts 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 of the
effect of rotation patterns on SOC stocks.
Original languageEnglish
Commissioning bodyUK Department for Environment, Food and Rural Affairs
Number of pages90
Publication statusPrint publication - Sep 2014

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