The effects of grassland management practices, and the role of hedgerows, on farmland carbon sequestration and storage
Agriculture is a major source for greenhouse gas (GHG) releases and is included in national GHG inventories. Land management decisions, such as those taken in agricultural landscapes, play a crucial role in carbon cycle dynamics with the ability to convert land from a carbon source to carbon sink. Practises influencing carbon sequestration and storage of land are currently missing from inventories of GHG releases at both national and local scales. The aims of this thesis were to evaluate the impacts on carbon sequestration in agricultural landscapes by the decisions taken by farmers and land managers. Determination of carbon dioxide (CO2) flux rates were used to investigate the effects of both grassland reseeding, during spring and autumn ploughing events, and land use change from grassland to cropland. The role that hedgerows play in agricultural landscapes to sequester and store carbon was also investigated as these ubiquitous features are routinely missing from carbon assessments. Grassland reseeding resulted in temporary releases of CO2 due to the removal of vegetative cover. Spring ploughing resulted in higher flux rates, however due to more rapid vegetation establishment less CO2 was released than ploughing in autumn. Land use change also resulted in releases of CO2 due to removal of vegetative cover. Methods of grassland rejuvenation and cropland establishment should maintain a cover to prevent net releases of CO2. Hedgerows can be considered as an ecosystem in terms of carbon cycling with carbon sequestration and partitioning occurring in a similar manner to forests. Published estimates of carbon storage are varied, depending on assessment methods, and further work is needed to lessen uncertainty. Hedges in Northern Ireland added an additional 44.15 – 73.27 t C ha-1 on an average area 0.94km2 (mean area of two study farms, Crossnacreevy and Loughgall) . Physical land uses as seen in agricultural systems are shown to impact upon carbon cycles, leading to either increased emissions or increased storage of carbon.
Carbon, carbon cycles, soils, ploughing, hedgerows, CO2 flux
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