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C.II EXPERIMENTAL ANALYSES OF THE IMPACTS OF TEMPORARY GRASSLANDS ON WEED POPULATIONS This second empirical chapter of the thesis has not been submitted for publication so far. The current status of this chapter is ‘article in preparation’. The chapter is presented as one single text to avoid redundancies, but it will later probably be divided into two articles. Manuscript 3: H Meiss, R Waldhardt, J Caneill, N Munier-Jolain (in preparation) Mechanisms affecting population dynamics of weeds in perennial forage crops. Abstract Perennial forage crops may have very strong impacts on weed communities, as suggested by weed surveys on commercial fields and field experiments. However, little is known about the mechanisms causing such impacts and many previous studies confounded the crop treatments with herbicide treatments. In a 2.5-years field experiment, population dynamics of 16 artificially sown and other naturally occurring weed species were compared between perennial forage crops and a succession of annual cereal crops both with contrasted management options but always without herbicides. Perennial crops differed by crop species (Medicago sativa vs. Dactylis glomerata), sowing season (autumn vs. spring) and cutting frequency (3 vs. 5 cuts per year). The succession of annual crops (winter wheat–intercrop–spring barley–intercrop) differed by the intercrop treatment (with or without autumn soil tillage and with or without a mustard cover crop). Total weed plant densities and aboveground crop and weed biomasses were measured every 1- 3 month during the whole vegetation period. Both showed decreasing tendencies in all treatments of perennial crops but increasing tendencies in the succession of annual crops. Species richness showed the same tendencies but the richness/abundance ratios improved with time in perennial crops and deteriorated in the annual crops. At the end of the experiment, the weed community composition differed most strongly between annual and perennial crop treatments. This was mainly caused by strong weed population increases of G. aparine, A. myosuroides and other annual weed species in all annual crop treatments. Among the 69
perennial crop treatments, differences between spring and autumn sown crops were much stronger than between the two cutting frequencies and the two crop species. Results suggested that several stages of the weed life cycle were affected by three main characteristics of perennial forage crops : A) The absence of soil tillage was probably the main reason for i) reduced germination and emergence rates in the perennial crops after the crop establishment phase, ii) increased survival of established weed plants and probably also iii) reduced weed seed survival, as seeds stay on the soil surface. B) The strong and temporally extended competition of the perennial crops reduced vegetative weed growth and seed production. C) The frequent hay cuttings destroyed the shoots and reduced seed production of weed plants that often showed lower regrowth and higher mortality rates than the perennial forage crops. In contrast, weeds were not able to profit from temporally reduced competition for light after hay cuttings. The rather complex experimental design and the frequent observation dates permitted disentangling some, but not all, of these mechanisms that acted often simultaneously, showed reinforcing or compensating interactions and cumulative effects on the weed life cycle. Key words: Plant population dynamic, temporary grassland, crop rotation, soil tillage, competition, cutting, regrowth, Integrated Weed Management, biodiversity. C.II.1 Introduction Today’s crop rotations are frequently very short (2-4 years) and often constituted by crops that provide rather similar weed growth conditions (e.g. only annual winter-sown crops). Therefore, weed species adapted to the conditions in these crops may be favoured in every year leading to high population growth rates which increases the need of intensive curative (chemical or mechanical) weed control. However, these techniques may have strong negative environmental side effects which are increasingly considered (e.g. groundwater pollution by 70
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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
Page 41 and 42: Table 3: Four strategies for combin
Page 43 and 44: otations is thus an obvious approac
Page 45 and 46: iv) the availability of cheap and e
Page 47 and 48: Clay & Aguilar (1998) compared the
Page 49 and 50: Heggenstaller & Liebman (2006) comp
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Page 53 and 54: A.V DIVERSIFIED CROPPING SYSTEM CON
Page 55 and 56: crops will thus probably show rathe
Page 57 and 58: annual crops while increasing organ
Page 59 and 60: • Which species are suppressed, w
Page 61 and 62: B OVERWIEW OF THE MATERIALS & METHO
Page 63 and 64: A) France B) Study site ~1000 km Pe
Page 65 and 66: perennial crops with different mana
Page 67 and 68: B.III.2.4 Cutting height In 2008, t
Page 69 and 70: B.IV.3 Design of the seed predation
Page 71 and 72: Agron. Sustain. Dev. 30 (2010) 657-
Page 73 and 74: Contrasting weed species compositio
Page 79 and 80: Mean frequency in perennial lucerne
Page 81 and 82: C.I.2 Article 2: Meiss, H., Médiè
Page 83 and 84: 332 H Meiss et al. communities (Boo
Page 85 and 86: 334 H Meiss et al. functional group
Page 87 and 88: 336 H Meiss et al. Table 3 Indicato
Page 89 and 90: 338 H Meiss et al. Relative frequen
Page 91: 340 H Meiss et al. MEISS H, MUNIER-
Page 95 and 96: PFCs might inhibit the successful g
Page 97 and 98: during winter), T10 without soil ti
Page 99 and 100: The viability and germination abili
Page 101 and 102: Table 8: Organic carbon and total n
Page 103 and 104: The development of weed species ric
Page 105 and 106: C.II.3.1.2 Dynamics of weed communi
Page 107 and 108: C.II.3.1.3 Dynamics of individual w
Page 109 and 110: Time Fig. 14: Temporal development
Page 111 and 112: At the end of the experiment in spr
Page 113 and 114: Difference sown - unsown (plants m
Page 115 and 116: Cumulated BM production (g m -2 ) 1
Page 117 and 118: Weed biomass (g m -2 ) 500 400 300
Page 119 and 120: Table 12: Factors differing between
Page 121 and 122: However, some differences in densit
Page 123 and 124: Table 13: Mechanisms causing the im
Page 125 and 126: 2007 and 2008, while big numbers of
Page 127 and 128: • Weed biomasses decreased in sum
Page 129 and 130: Our results show that different mec
Page 131 and 132: including exotic species (Palmer an
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Page 141 and 142: 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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When both treatments were combined,
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C.IV WEED SEED PREDATION C.IV.1 Art
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XIII ème COLLOQUE INTERNATIONAL SU
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produites restent à la surface du
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Tableau 1 : Liste des espèces adve
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Insectes prédateurs Les principaux
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C.IV.3 Article 8: Meiss, H., Lagade
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Table 1 Studies investigating the i
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Table 2 Overview showing (i) mean s
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higher weed seed losses (e.g., Mena
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D GENERAL DISCUSSION Data from weed
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The first two limits could be addre
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composition that may be compared to
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Frequency in field experiment (Epoi
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crops (Clay and Aguilar, 1998; Card
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Such diversified crop rotations cou
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the leaves (needed for photosynthes
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field margin strips (compare Articl
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1) The absence of soil tillage and
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D.III.2 Predicting weed regrowth af
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Future studies must determine the s
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(illustrated in Fig. 24). Later, re
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D.III.3 Factors determining weed se
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governing the presence and abundanc
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natural conditions, weed species po
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This PhD research project documente
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area needed for crop production. Gl
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seed characteristics, tillage and s
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Fried G., S. Petit, F. Dessaint, X.
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at the Eastern base of the Meissner
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Lindegarth M., L. Gamfeldt. (2005)
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Murphy S.D., D.R. Clements, S. Bela
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affected by experimental substrate.
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Vincent G., M. Ahmim. (1985) Note o
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ANNEXES ANNEXE 1: KEY WORDS IN ENGL
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genetically modified crop varieties
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ANNEXE 3: WEED SPECIES OF THE LARGE
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Name of species /genera Code Freq.
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Name of species /genera Code Freq.
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ERKLÄRUNG (DECLARATION FOR THE GIE
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