Constraining and validating models for investigating the impact of management on ecosystem carbon flows and changes in soil organic carbon (SOC)
Rachel Murphy
In accordance with the Paris Agreement, Ireland has pledged to reduce its greenhouse gas emissions
by 30% between 2021 and 2030 relative to baseline emissions in 2005. Of this emission reduction
target, 5.6% can be achieved through offsetting emissions by soil organic carbon (SOC) sequestration
by removing CO 2 from the atmosphere and storing it in soils. This is of particular importance to Irish
agricultural landscapes, as the agricultural sector was responsible for 37.1% of total national GHG
emissions in 2020, of which agricultural soils accounted for one third of these reported emissions.
Grassland systems managed for livestock and food production represent 58% of the land surface
area in Ireland, and therefore can serve as a tool for GHG mitigation through SOC sequestration.
Rates of SOC sequestration in grassland systems will vary according to management, soil type, climate as well as the processes that govern long-term SOC storage. To date it is still a difficult task to accurately quantify rates of SOC sequestration within managed grasslands as C inputs are small (
i.e. > 1 t C ha -1 ) relative to the background SOC (approximately 150 – 250 t C ha -1 ) in grassland systems with mineral soils. Presently, Ireland uses a default (Tier 1) emission factor for estimating SOC losses due to land management and land-use factors from grassland systems, however this
approach fails to account for variability in SOC losses due to soil type, fertility as well as management intensity. The aim of this research is to develop and validate process based models to stimulate ecosystem and soil C cycling that will allow for more precise and holistic quantifications of
SOC losses from managed grassland with mineral soils, and in turn will be incorporated into national GHG inventories. This will involve measurements of both ecosystem scale fluxes of CO 2 and field scale measurements of SOC pools associated with pasture management which will serve to calibrate and validate the proposed process based models.