Changes in organic matter contents and carbon stocks in Dutch soils, 1998–2018

Changes in soil organic matter (SOM) content and carbon (SOC) stock the 0–30 cm 30–100 layers between 1998 2018 Netherlands were estimated by repeated sampling of 1152 locations Soil Sampling Programme (SSP). These selected following a stratified simple random design. We discuss various barriers we met: restricted accuracy information on bulk density, uncertainties due to positional errors, differences support, changes laboratory analysis methods since 1998. Domains interest such as mineral soils defined either basis stratification SSP sample (geomatching) or profiles observed at (classmatching). The mean SOM changed significantly layer (-17.68 gkg-1) entire area (non-built-up Netherlands) (at 5% significance level). A decrease could be shown for under cropland if classmatching was applied level), but no change this remaining domains interest, whether geomatching applied. For soils, significant classmatching: ?8.59 gkg-1 ?4.75 grassland. calculations indicate that SOC stocks decreased both density data needs improved future measurements increase changes.