Diversifying crop rotations with temporary grasslands - Université de ...

perennial crops might thus be a valuable complement of other IWM techniques, enabling a
high yielding crop production and a reduced need for curative weed control including
herbicides. In this way, it might contribute to combining high yielding crop production and
biodiversity conservation at the dynamic landscape scale. However, it is e.g. not clear whether
the species favoured by the perennial crops create new weed problems or whether they are
quickly suppressed in the following annual crops.
A.V.2 Expected impacts on biodiversity
Different elements of farmland biodiversity will likely profit from the cropping system
concept based on the temporal partition of 3 agro-ecological functions. The replacement of
herbicides by alternative IWM-techniques may particularly benefit herbicide-sensitive plant
species, and thus also organisms feeding or reproducing on the weeds. The introduction of
untilled stubble fields as an exemplary ‘large-area’ agri-environment scheme would improve
the habitat quality and food availability for many organisms including birds, mammals,
beetles, ants, snails and crickets (Siriwardena et al., 2006). Gillings et al. (2005) showed that
the introduction of 10-20 ha overwinter stubbles per 1 km² (1-2% of the area) could reverse
the negative population trends of farmland birds in the UK. Finally, the permanent vegetation
cover and the lack of soil tillage during several years in the PFCs may provide a rather stable
habitat for various organisms that can not survive in annual arable crops, or that need both
annual crops and grasslands in close neighbourhood (Summers, 1998; Entz et al., 2002;
Buckingham et al., 2006; Henderson et al., 2009). Unlike annual crops, PFCs can provide
plant and invertebrate food for higher organisms throughout the year (Tucker, 1992). The
biodiversity value of temporary grasslands is probably intermediate between annual crops and
permanent grasslands (Thiebaud et al., 2001).
A.V.3 Expected impacts on the environment
All three proposed modifications may also have several, mostly beneficial, effects on the
physical environment. The reduction of herbicide use may reduce soil and water pollution and
the other drawbacks of herbicides (see section A.II.2). However, some alternative weed
control techniques may have negative environmental impacts too. Soil tillage used for weed
destruction needs a lot of (fossil) energy and may increase soil erosion and nutrients leaching
risks. In contrast, perennial crops and stubble fields are both characterized by temporarily
omitted soil tillage, which may thus reduce nutrient leaching and soil erosion compared to
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