Optimising carbon storage by land-management

Abstract

As the UK’s largest non-government land-owner, the National Trust is committed to reducing its impact on climate change, recognising the importance of soil organic carbon (SOC), and its need for preservation. To establish if land-management could be optimised to increase carbon storage, ‘The Wallington Carbon Footprint Project’ was implemented. This study aimed to measure the Wallington Estate’s carbon stock, establish what controls SOC, identify carbon under-saturated soils, and make land-management change to increase SOC. To achieve these objectives a soil sampling campaign and land-use survey were undertaken at Wallington, with further sampling at a verification site in Cambridgeshire. Land-use intervention trials measuring carbon fluxes and SOC change were combined with computer modelling and questionnaires, to assess the impacts of land-use and management change on SOC. A land carbon stock of 845 Kt (60 Kt within biomass, and 785 Kt within soils) was estimated for Wallington, with the greatest control on SOC identified as grassland landmanagement. Other controls on SOC were: land-use, soil series, altitude, soil pH and landuse history, indicating that these should be used in all estimates of SOC distribution and stock. A possible link between phosphate fertilisation and SOC accumulation under grassland was identified; however this was not confirmed in a year long field trial. Incorporation of charcoal into soils was identified as a method of carbon sequestration, with a simultaneous reduction in nitrate loss from soil. Surface application to grasslands revealed no detrimental effects on soils, grassland productivity or water quality. Further trials investigated the impacts of arable conversion to short rotation coppice willow, and of peatland afforestation, both indentifying losses of SOC following the land-use change. Measurement of biomass carbon gains, full life cycle assessment of the each landuse, and the impacts of varying types of biochar are required before firm conclusions regarding land-use change and carbon sequestration can be made