Higher carbon sequestration on Swedish dairy farms compared with other farm types as revealed by national soil inventories

Abstract

Small changes in the large stock of soil organic carbon (SOC) can have a substantial influence on the climate impact of agriculture. We used information from a Swedish soil monitoring program, in combination with farm census data, to analyze decadal SOC concentrations and SOC stock changes on dairy farms compared with other farm types, and to quantify the climate impact of these changes on dairy farms. Soil monitoring data included topsoil samples from two inventories on 159 dairy farms, 86 beef farms, 318 arable farms, and 13 pig farms, taken at the same locations in 2001–2007 and 2011–2017. Concentrations of SOC on dairy farms (3.0%) were significantly higher than on arable farms (2.3%) and pig farms (2.4%), but not significantly different from beef farms (3.1%). SOC concentration was correlated with proportion of ley at farm scale. SOC stocks in the upper 20 cm increased significantly on dairy, beef, and arable farms, by 0.38, 0.14, and 0.21 Mg C ha−1 year−1, respectively, between 2001–2007 and 2011–2017. For dairy farms, this corresponded to −1.4 Mg CO2 ha−1 and approximately −0.22 kg CO2 kg−1 energy-corrected milk, demonstrating that SOC changes could have a substantial influence on the climate footprint of milk.