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

succession of annual crops, plant communities were characterized by several common annual
weed species including those often reported as problematic in annual cereal crops such as G.
aparine, A. myosuroides, F. convolvulus, P. aviculare, P. rhoeas, and Sinapis arvensis.
C.II.4.2 Grassland management practices
While crop management options could not be distinguished in the large-scale weed surveys,
the field experiment permitted to compare tree treatment factors that were partially crossed:
two different perennial crop species, two sowing seasons and two cutting frequencies. Such
comparisons were rarely done in the previously published studies (reviewed in Article 1,
Meiss et al., 2010a). Weeds reacted differently to these treatments, which will be discussed in
the following. These differences may give first indications on the optimal perennial crop
management and may inform about the mechanisms potentially underlying the impacts.
However, one should keep in mind that the differences between these treatments were mostly
much less strong than between annual and perennial crops (see overview in Table 11).
C.II.4.2.1 Sowing date
Among the three treatment factors, crop sowing date (autumn vs. spring) had strongest
impacts on weed species composition, while the total weed densities were rather similar. In
the emerged weed vegetation, the differences in species composition decreased with time
(Table 9). These results highlight the importance of the establishment phase of the perennial
crop. Sowing date is known to have strong impacts on weed species composition in annual
crops (Hald, 1999), but such impacts have never been demonstrated for perennial crops.
C.II.4.2.2 Crop species
Although legume (Medicago sativa) and grass (Dactylis glomerata) crops may differ in
various aspects including temporal growth dynamics, nitrogen fixation and fertilisation
regimes, competitive ability and allelopathy (Table 12), crop species was not the most
important treatment factor in the field experiment (see overview in Table 11). This is in line
with previous studies by Andersson and Milberg (1996; , 1998), who detected strong
differences in weed density and species composition between annual and perennial ley crops
during 6-year crop rotations, but not between grass and grass-legume leys. Similarly,
Bellinder et al. (2004), did not find differences in weed seed banks after alfalfa and clover
forage crops.
97