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Weed seeds i) Presence, abundance - Weed community & pop density (crop rotation, past weed control) - Plant phenology seed prod. - Seed burial - Spatial seed distribution - ii) Seed traits - Weed species: - Mass, dimensions - Physical characteristics - Chemical composition - Seed age & viability Environment Pedo-climatic conditions - soil, season, weather, … Landscape configuration - … Cropping system, farming practices - Crop type - vegetation cover - Soil tillage, sowing, intercropping - Fertilizing, irrigation, drainage - Insecticides, herbicides - Crop harvest, mowing, cutting Synchronization Match Fig. 25: Overview of factors determining post-dispersal weed seed predation. Factors determining the presence and abundance of weed seeds (factor group i) as well as the presence, abundance and activity of seed predators (iii) vary according to the environment (upper box), which is determined by pedo-climatic conditions, landscape parameters and the cropping system (illustrated by the black arrows). These factors may thus be manipulated by the farmer through the choice of a crop and associated management practices (soil tillage, pesticides, harvest etc.). This is not the case for the specific traits of weed seeds (ii) and the diets, preferences and behaviour of the seed predators (iv). These characteristics might be considered as fixed parameters of the plant and animal species. Following this scheme, seed predation may only take place if the predators’ preferences correspond to the seed characteristics ↔iv) (ii and if there is a temporal synchronisation between the presence of the predators and weed seed shed ↔iii, (i Fig. 25) (Van Klinken, 2005; Gallandt, 2006). The species-specific characteristics of the seeds (ii) and of the predators (vi) are stable and can therefore not be manipulated to enhance weed seed predation. In contrast, most of the factors 177 Seed predators iii) Presence, abundance, activity - Regional species pool - Dispersal abilities - Favorable habitat (shelter, micro-climat, food) - carnivores, parasitoïds,… iv) Diet, preferences, behaviour - Species, guilds - Energy need, hunger - Alternative food items - …
governing the presence and abundance of seeds (i) and predators (iii) are strongly dependent on the environment such as the pedo-climatic conditions and landscape characteristics and, in the case of agro-ecosystems, on the cropping system and the different farming practices (Fig. 25). One of these environmental factors determining the habitat quality for seed predators, vegetation cover, has been shown in Article 8 to have a positive impact on seed predation rate. Future developments of models simulating weed seed predation might use this information. However, the lack of mechanistic knowledge on the impact of vegetation cover, the differences between weed seeds and all the other factors still hampers the proposition of a mechanistic modelling framework at this stage. D.IV GENERAL CONCLUSION The results of this research project provide direct evidence that perennial forage crops might play a significant role in arable crop rotations, both by contributing to the management of weeds and by maintaining or increasing the floristic diversity. The typical trajectories of weed communities identified from the preceding crop to the crop following alfalfa in the space-fortime substitution design in the large-scale surveys were consistent with the more precise, longitudinal observations of community and population dynamics in the field experiment. In both studies, strong changes in the weed species composition away from the most noxious species in annual crops were observed. Two examples of weed species that were clearly suppressed by PFCs were Galium aparine and Cirsium arvense, two very competitive species often requiring specific supplementary herbicide applications in current cereal-based cropping systems. Most important, the effects of PFCs on weed communities were still marked in the subsequent annual crop, hence indicating that the impacts not only concerned the currently emerged flora, but also the belowground seed bank. The observations thus validated one hypothesis of the project, i.e. the value of PFCs as a significant component of Integrated Weed Management. Introducing PFCs in arable crop rotations is thus a powerful means for weed management, probably allowing reductions in herbicides or excessive mechanical weed control. Moreover, diversified crop rotations including annual and perennial crops creates highly variable selection pressures for weeds, and this may also reduce the risk for selecting herbicide resistant weed biotypes. According to the large-scale surveys, the species richness and the richness/abundance ratios were somewhat improved in alfalfa compared to annual grain crops, increasing floristic 178
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Diversifying crop rotations with te
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In Chizé, I am indebted to all the
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Talks . ...........................
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C.II.4.1 Differences between crop t
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INDEX OF FIGURES Fig. 1: Population
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ABSTRACTS (ENGLISH, FRENCH & GERMAN
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Extended summary in English Résum
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Extended summary in English Résum
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CONTEXT AND FUNDING This thesis is
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THESIS ORGANISATION This thesis ent
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8) Meiss, H., Lagadec, L. L., Munie
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Posters . 1) Meiss, H., Waldhardt,
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2007). Agriculture is increasingly
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term considerations (Munier-Jolain
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problematic for the production of d
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Newton, 2004). Several bird species
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A.III APPROACHES TO ALLEVIATE THE
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and higher production costs or even
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competitive yield loss (Cousens, 19
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2006; Makowski et al., 2007). Moreo
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Table 3: Four strategies for combin
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otations is thus an obvious approac
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iv) the availability of cheap and e
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Clay & Aguilar (1998) compared the
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Heggenstaller & Liebman (2006) comp
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growth of any (crop or weed) plant
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A.V DIVERSIFIED CROPPING SYSTEM CON
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crops will thus probably show rathe
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annual crops while increasing organ
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• Which species are suppressed, w
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B OVERWIEW OF THE MATERIALS & METHO
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A) France B) Study site ~1000 km Pe
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perennial crops with different mana
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B.III.2.4 Cutting height In 2008, t
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B.IV.3 Design of the seed predation
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Agron. Sustain. Dev. 30 (2010) 657-
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Contrasting weed species compositio
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Mean frequency in perennial lucerne
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C.I.2 Article 2: Meiss, H., Médiè
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332 H Meiss et al. communities (Boo
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334 H Meiss et al. functional group
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336 H Meiss et al. Table 3 Indicato
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338 H Meiss et al. Relative frequen
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340 H Meiss et al. MEISS H, MUNIER-
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perennial crop treatments, differen
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PFCs might inhibit the successful g
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during winter), T10 without soil ti
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The viability and germination abili
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Table 8: Organic carbon and total n
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The development of weed species ric
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C.II.3.1.2 Dynamics of weed communi
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C.II.3.1.3 Dynamics of individual w
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Time Fig. 14: Temporal development
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At the end of the experiment in spr
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Difference sown - unsown (plants m
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Cumulated BM production (g m -2 ) 1
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Weed biomass (g m -2 ) 500 400 300
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Table 12: Factors differing between
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However, some differences in densit
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Table 13: Mechanisms causing the im
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2007 and 2008, while big numbers of
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• Weed biomasses decreased in sum
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Our results show that different mec
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including exotic species (Palmer an
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XIII ème COLLOQUE INTERNATIONAL SU
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irradiation,…), and (ii) biotic i
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Table I: Species included in the ex
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Fig. 2: Mean biomass (harvestable d
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Page 151 and 152: C.IV WEED SEED PREDATION C.IV.1 Art
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Page 163 and 164: Tableau 1 : Liste des espèces adve
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Page 167 and 168: C.IV.3 Article 8: Meiss, H., Lagade
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Page 171 and 172: Table 2 Overview showing (i) mean s
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Page 175 and 176: D GENERAL DISCUSSION Data from weed
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Page 207 and 208: area needed for crop production. Gl
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Page 219 and 220: affected by experimental substrate.
Page 221 and 222: Vincent G., M. Ahmim. (1985) Note o
Page 223 and 224: ANNEXES ANNEXE 1: KEY WORDS IN ENGL
Page 225 and 226: genetically modified crop varieties
Page 227 and 228: ANNEXE 3: WEED SPECIES OF THE LARGE
Page 229 and 230: Name of species /genera Code Freq.
Page 231 and 232: Name of species /genera Code Freq.
Page 233 and 234: ERKLÄRUNG (DECLARATION FOR THE GIE
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