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

B OVERWIEW OF THE MATERIALS & METHODS
B.I ANALYZING THE IMPACTS OF TEMPORARY GRASSLANDS ON
WEED COMMUNITIES: LARGE-SCALE FIELD SURVEYS
B.I.1 Rationale
The objective of this study was to analyze the impacts of arable crop rotation including PFCs
on weed communities. The analysis was done in two steps.
The first step (corresponding to Article 1) consisted in a simple comparison of the weed
communities in 7 different current crops comprising alfalfa (Medicago sativa)-based forage
crops, the most frequent perennial crop, and six annual crops chosen among the most frequent
crops in the study region (Fig. 9). Differences in weed communities between perennial and
annual crops were analysed and compared to the overall weed community variability in the
region dominated by annual crops. Hypothetical differences in the species composition would
be a first indication that annual and perennial crops could promote different weed species.
The second step (corresponding to Article 2) consisted in an analysis of the weed community
trajectories during crop rotations including PFCs using a space-for-time-substitution design.
The weed species composition, richness and frequency of functional groups were compared
between four groups of fields representing four stages of a crop rotation: a) winter wheat
fields following several years of annual crops, b) first-year alfalfa fields following annual
crops, c) older alfalfa fields, and d) winter wheat fields following perennial alfalfa (see Article
2 for details). The second analyse was thus limited to the most frequent annual crop (winter
wheat) and the most frequent perennial crop (alfalfa) of the Chizé region. It included the crop
sequence histories of each field permitting to analyze long-term effects of PFCs and to obtain
information on weed community trajectories during crop rotations including annual and
perennial crops.
B.I.2 Methods in analyzing weed composition and crop rotation histories
These two analyses were based on weed surveys in the ‘Chizé’ research area (zone atelier
‘Plaine et Val de Sèvre’), comprising about 18000 fields and 450 km², situated in the Niort
plain in Poitou-Charentes, western France (Fig. 9). Weed surveys were realized in 2006, 2007,
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