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

very dissimilar to annual crops, and other benefits to biodiversity, environment and crop
production.
A.III.9 Perennial forage crops (PFCs)
PFCs may consist of various perennial legume species such as lucerne/alfalfa (Medicago
sativa), different clovers (Trifolium sp.), and several other legume species (Fabaceae family),
as well as different grasses such as Dactylis glomerata, Festuca sp., Lolium sp., Phleum
pratens, and Poa pratensis. They are often sown as legume-grass mixtures (Freyer, 2003).
Such crops are habitually used for livestock forage production in mixed farming systems
(mown for hay or silage or grazed as pasture) (Summers, 1998; Sulc and Tracy, 2007). In
contrast to all annual crops, such crops last on the field for more than one year, typically about
2-5 years, sometimes even longer. They may thus be seen as intermediate between annual
crops and permanent grasslands or pastures. In the literature, they are referred to with various
names including ‘temporary grassland’ (TG), ‘artificial grasslands’, ‘pluriannual crop’, ‘ley
crop’, ‘sod crop’, ‘fodder crop’, ‘hay crop’ or even ‘cleaning crop’. Since 1700, sown PFCs
substituted the fallow phase of crop rotations in ‘alternate husbandry’ systems (see A.III.8).
Both phases may increase soil fertility after depletion by annual crops and disrupt the cycle of
diseases, pests and weeds (Freyer, 2003).
During the last 40 years, such ‘mixed’ crop–livestock farming systems have declined,
especially in intensive conventional farming systems, while PFCs remained more frequent in
organic and integrated systems (Freyer, 2003). In France, the area of temporary grasslands
was reduced from 1.5*10 6 ha in 1970 to 1.1*10 6 ha in 2000 (-25%), while the surface of all
annual crops was strongly increased from 12.2*10 6 ha to 15.2*10 6
ha (+25%) during the same
period (Bisault, 2008). Major reasons for this decline include
i) the splitting of cereal and livestock production to different farms and different
regions,
ii) the substitution of grass- or roughage-based forages by grain-based forages in
intensive livestock production systems,
iii) the availability of tractors replacing draught animals that needed an on-farm forage
production, and
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