Quantifying baseline soil organic carbon (SOC) stocks to allow establishment of robust carbon accounting framework for sustainable agriculture in Ireland

The soil organic carbon (SOC) and stocks mediate pivotal ecosystem services such as carbon sequestration, climate regulation by mitigating greenhouse gas emissions, nutrient cycling, provisioning habitats for organisms, water supply, and production of food, fiber and fuel. In agricultural systems, multiple factors including climate, soil types, vegetation, and land management affect the SOC dynamics. However, the coupled impacts among these factors on SOC stocks at farm and regional scale are still unknown. Therefore, it is crucial to expand our understanding of carbon cycle under different scenarios to develop more sustainable agro-ecosystems at national level. To achieve this, Teagasc is leading the Signpost Program a multiannual sampling campaign aiming to build an accurate baseline of SOC stocks across different soil types, land uses and management regimes in Ireland. This will help to understand the carbon dynamics in Irish agricultural soils, revealing the composition and stability of SOC in depth. To build the baseline for longtime soil carbon observatory, SOC data and soil health indicators for 148 soil profiles have been collected to date within 37 farms across the country. The method for site selection was based on combination of geographic information system (GIS) techniques and the catena approach, covering different climatic regions, soil types, and farming systems along the dominant hillslope within each farm. The soil samples were taken at each 15 cm increment up to 60 cm soil depth. The baseline data includes estimation of chemical properties such as potassium (K) and phosphorus (P) obtained by Morgan’s extraction; pH, total nitrogen (N), total carbon (C), and organic carbon (SOC); aluminum (Al), calcium (Ca), Magnesium (Mg), and phosphorus (P). It also includes physical properties such as bulk density based on three replicates per each range of sampling depth and finally clay, silt, and sand content to be assessed by spectroscopy measurements. Finally, SOC stocks across P scenarios, C/N ratio, and C:N:P ratios are estimated to understand the capacity of soils to sequester carbon and the nutrients dynamics under different management regimes and soil types. The Signpost initiative emphasizes soil management practices with long-term benefits for the environment and expand knowledge to contribute to sequestering carbon, improving overall soil health to support progression of sustainable agricultural systems.