According to the paper presented at the Teagasc ‘Counting Carbon: Science and Practice Conference‘ this week, Ireland currently uses an Intergovernmental Panel on Climate Change (IPCC) Tier 1 approach for calculating soil C sequestration on grassland on mineral soils.
However, this Tier 1 approach does not fully represent Irish farming conditions or measured data, leading to uncertainty.
To address this, Ireland needs measured CO2 flux and C stock data across different soil types, management practices, and land uses, according to senior researcher with Teagasc, Giulia Bondi, who presented the paper at the conference.
This would enable Ireland to develop Tier 2 approach that would enhance accuracy in the national inventory for land use and land management.
Soil carbon sequestration
The conference heard that global warming is the long-term increase in the earth’s temperature due to the accumulation of greenhouse gases (GHGs) in the atmosphere, such as carbon dioxide (CO2).
Carbon sequestration is understood to help reduce global warming by removing CO2 from the atmosphere and in turn, offsetting the warming effect.
Referencing further research, Giulia Bondi’s presentation outlined that a framework for climate-smart land management for Ireland incorporates a three-step approach to optimise carbon dynamics and mitigate climate change impacts.
Firstly, it focuses on maintaining existing C stocks, recognising the crucial role of peatlands, which occupy approximately 20% of land but contain over 53% of carbon stocks, acting as hotspots for carbon sequestration.
Secondly, the framework aims to prevent new emissions from emission-sensitive soils, thereby mitigating further atmospheric carbon release.
This includes drained peats, or mineral soils moving from grasslands to arable (tillage), which can release significant amounts of stored carbon into the atmosphere, the conference heard.
Thirdly, it emphasises enhancing long-term carbon sequestration in grassland soils and through land use changes such as afforestation.
This holistic approach not only prevents carbon losses but also actively promotes carbon accumulation, contributing to a more sustainable and climate-resilient land management system, the Teagasc researcher outlined.
Carbon sinks vs carbon stocks
Teagas has stated that there is often confusion between the concept of carbon sequestration and carbon stocks.
Soil carbon stocks represent the total amount of C (carbon) stored in an area, to a specific soil depth on a specific date. It is typically measured as tonnes of carbon per hectare (t C/ha).
Carbon sequestration refers to the change in soil carbon stocks between one sampling date and another. It is the net change in soil C stock over time often referred to as carbon stock change.
Soil carbon sequestration is when carbon from the air is stored in the soil. Plants take in CO2 during photosynthesis and store carbon in their leaves and stems. When plants die, this carbon goes into the soil.
Soil microorganisms break down plant residues, releasing some carbon back into the air, but some remains in the soil as you can see in the picture below.
Soil can reduce atmospheric CO2 if it stores more carbon than it releases. The balance depends on land use, land management, soil type, and environmental conditions, and can shift quickly from storing to releasing carbon.
The typical carbon balance for an improved Irish grassland soil indicated the potential range in soil carbon sequestration ranges from 1.5t to 4t CO2/ha per year, according to Teagasc researchers.
While Irish soils have substantial carbon stocks, Teagasc suggests that key question remain – are we adding to or depleting these stocks? How permanent is soil C sequestration?
Research shows that grasslands usually store carbon, but there is uncertainty about how much they store and how management and climate affect this.
The conclusion is that improving soil carbon sequestration and emissions estimates involves using a multiscale approach.
Bondi explained to the attendees at the conference that this includes measuring fluxes at the field and farm levels, developing national soil carbon baselines, and using modelling techniques.
The conference heard that grassland soils in Ireland store significant amounts of carbon, approximately 440t CO2/ha or an estimated 1,800Mt CO2 across all mineral soils.
Teagasc has said that managing soil carbon effectively can significantly reduce atmospheric CO2 concentrations and improve agricultural productivity.