Land-use intensification
Land-use intensification was the second strongest GC impacting soil
fauna communities. When looking at the different environmental stressors
of land-use intensification, all were significantly negatively impacting
soil fauna, although the shift from an organic system to an inorganic
system, a press stressor, and the intensification of tillage practices,
a pulse stressor, resulted in the greatest decrease. Previous
meta-analyses have also found intensification of tillage practices to be
detrimental to soil fauna . Tillage causes direct mortality and
destruction of habitat, which exposes soil organisms to predators .
However, effects can also be indirect and longer term, through a
reduction of soil structure (limiting access to nutrient resources,
especially for smaller organisms, and increasing exposure to an
environment that may result in desiccation), changes in plant community
composition altering resource quality, and reduction in soil organic
matter at the surface . This highlights the weakness of using just a
single trait of an environmental stressor, and shows the need to
consider more than one characteristic in future studies .
It is difficult to pin-point the exact agricultural practices that
promote soil biodiversity in organic systems, because organic farming
specifications depend on countries, crops, and other factors . Based on
previous meta-analyses the decline in biodiversity may be the result of
the shift in nutrient addition regimes, as it is probable that the
strong decline was most associated with the change from organic
fertilisers and reduction in mulch. The addition/retention of mulch
(plus other soil amendments) and organic fertilisers were particularly
beneficial in this analysis, as well as others . Individually, these
components promote soil biodiversity (see below), and in concert could
provide even greater benefits to the soil community. However, as the
addition of pesticides (singularly within the pollutants category) also
significantly negatively impacted soil communities, the shift away from
high pesticide use cannot be ruled out as a contributor to the
positivity of organic agricultural systems. What is interesting to note
is the effect of the different land-use intensification types interacted
with the body size of the organisms, with macro-fauna (predominantly
comprised of earthworms) being most negatively impacted. Given that
earthworms mostly benefitted from the addition of nutrient enrichment
there is some indication that, at least for earthworms, the nutrient
enrichment aspect of organic agriculture may be the most important
(Figure 4).