Fig. 9: Distribution of observations of soil organic carbon (SOC) density.

Spatial distribution and representativeness of soil samples in different periods at depths of 0–15 cm (a). The median, mean (yellow triangle), and interquartile range of SOC density for samples along the vertical soil profile, note that numbers of samples from different depths are shown (i.e., N[1] represents the number of the first layer) (b).