The nutrients are deep down in the active layer anyway, not high up near the surface, which is the part of the active layer most affected by run-off.

One major problem is that degraded soils become compacted and so absorb less water, which then tends to run off the surface, taking topsoil with it.

As more droplets are attracted, they spread out and eventually join together and run off the surface-as they do on a pane of glass.