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