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

problematic for the production of drinking water, and public authorities have established rules
and targets for improving the quality of ground- and surface waters, such as the EU Water
Framework Directive (Directive 2000/60/EC).
Due to these environmental, economic and agronomic problems and the possible impacts on
human health, the reliance of crop production on herbicides should be reduced (Bastiaans et
al., 2000; Nazarko et al., 2005; Blackshaw et al., 2006). However, chemical weed control
could not simply be substituted by other curative techniques such as mechanical or thermal
weed control. These techniques may have reduced efficiencies, problems of selectivity and
also high economic and ecological costs. For example, intensive soil tillage used as
mechanical weed control may need a lot of labour time and energy, may damage the crops,
increase soil erosion, nitrate and carbon losses and may also be detrimental to soil organisms
(Stoate et al., 2001).
A.II.3 Weeds & biodiversity
During the last decades, arable weeds showed very strong declines in abundances and
diversity in many farming systems worldwide (Andreasen et al., 1996; Sutcliffe and Kay,
2000; van Elsen, 2000). In the UK, where biodiversity-issues are well studied and published,
farmland holds more scarce and threatened plant species than any other habitat (Rich and
Woodruff, 1996), which may also be the case in many other countries. In France, about 42%
of plant species richness has been lost during the last 30 years in arable fields in Côte-d’Or, a
typical region of intensive agriculture (Fried et al., 2009). This was probably due to changing
agronomic practices including a) improvements in weed control, b) better crop seed cleaning
techniques, c) the simplification of crop rotations including the strong reductions in spring
sown crops and perennial crops and the specialisations of farms and regions to either arable
crops or livestock farming, d) the use of more competitive crops (caused inter alia by higher
fertilizer use), and e) the simplification of farmed landscapes including the increase in field
size and removal of hedges and other non-crop elements (Robinson and Sutherland, 2002;
Benton et al., 2003; Gabriel et al., 2005; Roschewitz et al., 2005). Many studies showed that
weed diversity is higher in more complex landscapes and in organically managed fields (see
the reviews of Bengtsson et al., 2005; Hole et al., 2005; and Tscharntke et al., 2005; and the
study of Hotze and van Elsen, 2006).
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