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

dans des conditions de compétition contrastées (présence ou absence de luzerne) et avec
ou sans fauche précoce (dispositif factoriel 2x2). La production de biomasse par plante a été
affectée par la fauche et par la compétition, et la combinaison des deux traitements a montré
un effet purement additif pour la plupart des espèces (ni affaiblissement, ni renforcement
disproportionnée des effets). Ces connaissances peuvent être utilisées pour concevoir des
systèmes de culture conciliant productivité et durabilité.
Mots-clés : Croissance post-fauche, Compétition, Prairies temporaires, Gestion Intégrée.
INTRODUCTION
Plant fitness may be reduced by physical disturbances destroying parts of the plant’s
biomass, competition for resources by neighbouring plants, and different stresses as defined
by Grime (1974). Therefore, plant population dynamics and communities may be structured
by these three processes. Physical disturbances may have various origins such as abiotic
factors (fire, frost, drought, inundation), biotic factors (herbivory, parasitism, grazing) or
human factors such as agricultural management (harvesting, mowing, soil tillage). In arable
fields, competition is the most important interaction between the cultivated crops and the
spontaneously growing weeds (Zimdahl, 2004): crop yield may be reduced by competitive
weeds and weed growth may be limited by competitive crops. On the other hand,
disturbances created by different kinds of field operations will affect the plants and are used
to suppress weeds.
Habitats are frequently distinguished by a dichotomy opposing competition and
disturbance: Competition is lower in frequently disturbed habitats and higher in undisturbed
habitats (Grime, 1974). However, both processes may also act in quick succession during the
same vegetation period, for example in perennial forage crops (lucernes, clovers, grasses)
sometimes called ‘temporary grasslands’. In contrast to the classical annual crops that
precede and follow them in long crop rotations, perennial crops remain in the field for about
2-6 years. Forage crops are mown 1-5 times per year for hay production creating
disturbances. After each cutting, they show quick regrowth leading to high levels of
competition during the whole vegetation period (except directly after mowing).
Perennial forage crops may have strong impacts on weed abundances and
community composition, as suggested by a survey of farmers (Entz et al., 1995), field
observations (Ominski et al., 1999), field experiments (Schoofs and Entz, 2000;
Heggenstaller and Liebman, 2006) and seed bank studies (Clay and Aguilar, 1998; Sjursen,
2001; Bellinder et al., 2004; Teasdale et al., 2004; Albrecht, 2005). Most of these studies
report reduced abundances of several problematic weed species after the cultivation of
perennial crops, which would be beneficial for the following crops, while other species may
profit from this crop type. Nevertheless, little is known about the mechanisms causing these
effects.
Various factors may govern the plant’s ability to survive and grow after cuttings or
other physical disturbances destroying large parts of the aboveground biomass. These
include i) the amount of green surface remaining after the disturbance for photosynthesis, ii)
the presence of intact buds (apical meristems) needed for resprouting and iii) the quantity of
C and N resources that can be remobilized for regrowth (reviewed in Meiss et al., 2008).
These three factors may be affected by different underlying variables such as (a) the
species functional group (annuals vs. perennials, grasses vs. broadleaved species,…) and
(b) the plant size (biomass), (c) morphology and (d) age (phenological stage) as well as (e)
cutting height, (f) date and (g) frequency (see references in Meiss et al., 2008). Nevertheless,
the plant regrowth capacity may also depend on general growth conditions (temperature,
pH,…) and availability of growth resources (light, water, nutrients) depending on (ii) other
farming operations, (ii) edaphic and climatic variables (soil type, nutrients, precipitation,
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