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

species composition was compared using Canonical Discriminant Analysis (CDA, Kenkel et
al., 2002). Afterwards, global and pairwise differences of species communities between
groups of fields were statistically tested using Analysis of Similarities (ANOSIM, Clarke,
1993), a robust non-parametric method adapted to multivariate data with many ‘zeros’ and not
necessarily following multivariate normal distributions. Indicator Species Analysis (ISA,
Dufrene and Legendre, 1997) was used to identify the weed species with the most contrasting
differences in presences and frequencies.
Functional groups (FG) were defined according to the species taxonomy (opposing grasses
and broad-leaved species), life cycle (opposing annual, intermediate and perennials species)
and morphology of broad-leaved annual species (opposing upright, creeping, rosette and other
species, see Article 2 for further details on FG definition and Annexe 3 for species repartition
to the eight FGs). While a lot of rare species had to be excluded from the multivariate
analysis, all species could be included in the analysis of functional groups (see Articles 1 and
2 for details on the methods).
B.II FIELD EXPERIMENTS ANALYZING THE IMPACTS OF
TEMPORARY GRASSLANDS ON WEED POPULATIONS
(EPOISSES)
B.II.1 Rationale
Previously published experimental results and large-scale weed surveys suggest strong
impacts of PFCs on weed population dynamics and community composition. However, the
impacts of PFC management options and the underlying mechanisms are not well understood.
This would also be necessary to construct predictive models. Therefore, a field experiment
was conducted to better understand the impacts of PFCs on different annual arable weeds. In
contrast to previous experiments, comparisons between annual and perennial crop treatments
are not confounded with differences in herbicide treatments.
B.II.2 Design of the field experiment
The field experiment was based on a comparison of 9 crop treatments with 4 replicate plots
(75m² each) distributed on the field of an experimental farm. Six crop treatments represented
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