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

approach may be to try to increase weed species diversity without increasing the total weed
abundance (see A.III.3) or to try to promote weed seed predation (see A.III.5).
Two contrasting strategies will be shortly discussed in section A.III.6 that are frequently
opposed in the literature: ‘spatial separation of farming and biodiversity’ vs. ‘integrating of
farming and biodiversityat the same place’. A promising ‘third way’ will be proposed in the
following. This approach consists of a temporal separation of these different functions within
the crop rotation, so that ‘production’ and ‘conservation’ phases of may form spatio-temporal
mosaics at the landscape scale (see A.III.7). Crop rotation may diversify the selection
pressures on wild organisms including weeds, animals and micro-organisms, which may have
advantages both for crop protection and farmland biodiversity (A.III.8). Special attention will
be paid to the diversification of crop rotations with perennial forage crops (PFC, also called
‘temporary grasslands’), as they may differ in several important aspects to annual crops (see
A.III.9).
A.III.2 Integrated Weed Management
Integrated Weed Management (IWM) emphasizes i) the combination of different preventive
and curative weed management techniques and ii) integration of knowledge on the weed
biology into the design of cropping systems (Gill and Holmes, 1997; Buhler et al., 2000;
Mortensen et al., 2000; Buhler, 2002; Westerman et al., 2005). IWM considers the causes of
weed problems rather than only reacting to existing weed infestations. It may provide the
farmer with a broader tool of techniques and principles that should diversify the selection
pressures against weeds and hamper the selection of herbicide resistances. There are various
cultural, physical, chemical, and biological techniques that may be used for integrated weed
management (see also reviews by Mortensen et al., 2000; Barberi, 2002; Buhler, 2002;
Hatcher and Melander, 2003; Blackshaw et al., 2006; Bastiaans et al., 2008):
Long-term cropping system experiments showed that Integrated Weed Management can
provide sufficient weed control and significantly reduce herbicide pollution (Chikowo et al.,
2009; Munier-Jolain et al., 2009). But despite these good agronomic and environmental
results in experiments, IWM is hardly introduced in real farms. Different factors may hamper
their large-scale adoption including an increased system complexity and sometimes a reduced
economic profitability (Leake, 1996; Bastiaans et al., 2008; Pardo G et al., in press). Today,
IWM principles are probably mainly used in organic farming, where herbicides are forbidden
11