l), our knowledge of the turn-over of forest soil humus is very incomplete. This is particularly true of the organic matter in soil horizons below the humus layer.

More information: Yunyu Zhang et al, Exchangeable manganese regulates carbon storage in the humus layer of the boreal forest, ...

There are two very clear examples in this stratigraphic section. They are two burrow holes created by fairly small animals originating in the humus layer and intruding into the shelly layer beneath.

For a long time, soil was all but ignored. But for years, the valuable humus layer has been thinning. Farmers in Brandenburg are clearly feeling the effects of this on their sandy fields.