Any compaction
of a soil can be recovered by physical power (like frost or mechanical lifting)
or by biological activities (roots, micro-organisms, worms…). Biological
activities get their power by life processes that depend on breathing. Due to
this reason, the measurement of carbon dioxide (CO2) in the pores is
a valid indicator for biological actions.
In biologically
active soils the percentage (on volume) of CO2 is about 0,3%, a bit higher
than in the outside air.
Directly
after traffic we observe a quick increment of CO2 in the soil pores.But after a
couple of hours the percentage of CO2 can go down again. We believe
that in this case the pores in the soil are opened again by biological
activities from all directions.Thus, though the specific soil
pressure may be high, when the affected volume of soil is small and the lateral
area is large as we have it with human footprints or animal steps, then recovery
happens very quickly.
When a
light tractor (< 5 t) drives on the soil, the impact is higher. For the
first few months, the percentage of CO2 is significantly higher, but
there is a tendency to recovering during the first year. Of course, much
depends on the gross weight of the tractor, the number of passes, the soil
type, the moisture… so, driving with tractors seems to approach the limits.
When a
harvester, which has a gross weight > 15 tons, drives on the soil, the
impact is so high, that the percentage of CO2 increases in the first
few months and may exceed the 1,0 %vol threshold. Over several
years there is no clear tendency towards recovery.
This
tendency gets clear as soon as heavy forest machines drive on the soil several
times. Here the soil shows no tendency for recovery.
