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

otations is thus an obvious approach to reduce the ‘weeds trade-off’, i.e. to combine high crop
yields, low reliance on pesticide and fertilizer inputs and high biodiversity (see Fig. 6).
Positive influence
Negative influence
C sequestration, Less nitrogen
leaching, soil erosion, energy use
Food
chain
Cropping diversity
rotation complexity,
+ temporary grasslands ?
Environment Biodiversity direct Crop Yield
Eutrophication, desertification
Pollution
Less predictive
environment
pesticides
20
pest regulation, pollination,…
beneficial
noxious
Competition, pests,…
Different habitats
fertilizer, water
Inputs
indirect
Nitrogen fixation, organic residues
Growth conditions + resources
Fig. 6: Simplified illustration of the trade-off between farming (crop yield), environmental protection and
biodiversity conservation.
The trade-off is mediated by influences of the farming inputs (pesticides, fertilizers and irrigation water) (positive
for crops, negative for environment and biodiversity). By increasing the crop diversity (using complex crop
rotations), some of the functions of the farming inputs (crop fertilisation, pest regulation) may be substituted,
which would have different beneficial effects on the environment and biodiversity.
The present work focalizes on the temporal diversity of crops in the framework of crop
rotations. Growing several crop species together at the same time (‘intercrops’, ‘companion
crops’ and ‘undersowing’ techniques) is another possibility to increase the crop diversity. It
may also be used for Integrated Weed Management and for increasing biodiversity in the
farmland (Liebman and Dyck, 1993; Palmer and Maurer, 1997) but will not be addressed in
this work.
Crop rotations may be diversified by introducing either (a) other annual ‘cash’ crops,
preferably with dissimilar characteristics, (b) ‘cover’ or ‘catch’ crops grown between
successive annual crops (replacing periods of bare soil) (Barberi, 2002; Smith and Gross,
2007), but also (c) perennial crops that last for several years on the field (Sebillotte, 1980;
Freyer, 2003) (see section A.III.9). Perennial crops may be of special interest for weed
management and biodiversity, as it may provide conditions for weeds (and animals) that are