Chemistry Reference
In-Depth Information
Topsoil compaction refers to damage to the ploughed layer of soil where
remediation or natural processes can assist with structural recovery following
damage. Subsoil compaction refers to damage below the plough layer, where
remedial measures to alleviate structural damage are not possible or are less
effective, resulting in more persistent damage. Soil compaction is classified as
harmful when saturated hydraulic conductivity and air capacity go below
certain values (,10 m day
21
and 5%, respectively).
17
Soil compaction occurs when an external mechanical stress from equipment
or livestock exceeds the mechanical stability of soil.
18
Many factors control the
susceptibility of soil to compaction, including the stress history from previous
traffic,
19
texture,
20
organic matter
21
and soil structure.
22
Most of these
properties also affect how well soil recovers from compaction through
subsequent cultivation
23
or the inherent resilience under natural weathering.
24
The amount of water in soil affects its mechanical stability to compaction.
As a consequence, precipitation changes predicted for the future could have
major implications.
25
Drier soils compact less than wetter soils. In the
European Union, the greening of the Common Agricultural Policy (CAP)
through the implementation of the Good Agricultural and Environmental
Code (GAEC) restricts access to fields when they are wet.
26
However,
providing accurate advice to farmers on when not to access land with
machinery or livestock is a challenge. Predicting the susceptibility of soil to
compaction is fraught with uncertainty because of the complexity of stress
transmission through soil and confounding factors such as the influence of soil
structure.
27
Subsoil compaction is viewed as a far greater threat
28
than topsoil
compaction, as the latter can be ameliorated to some extent by soil cultivation
and natural processes.
21,29
The impacts of subsoil compaction include reduced
crop yields, poor drainage and increased overland flow.
30-32
d
n
1
r
2
n
g
|
8
Compaction also
soil,
24
alters
microbial
habitats
in
so
it
could
have
implications
for
biodiversity.
33
2.1.1 Extent of Compaction
Evidence of soil compaction is extensive globally, particularly under intensive
agriculture where machinery weights are large.
28,34
About 4% (69.3 Mha) of
anthropogenic soil degradation globally has been attributed to soil compac-
tion,
35
but this estimate is over 20 years old and limited to extreme compaction
where effects are evident from crop failure or severe surface damage. An
analysis of soil on 156 farms in Scotland by Ball
36
found that many had been
affected by soil compaction. This study followed on from anecdotal evidence
for Scotland collected by Soane,
37
who found widespread concern about soil
compaction from 1421 farmers who were surveyed.
Soil compaction can be out of sight and out of mind. The effects are not
always evident and sometimes remedied unknowingly through the increased
application of fertilisers. Simply by managing soil to have a smaller bulk
