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

composition that may be compared to the differences between spring and autumn sown annual
crops. However, these differences decreased with time in the emerged vegetation. In contrast,
differences between the two crop species (alfalfa vs. cocksfoot) and the two cutting
frequencies (3 vs. 5 cuts per year) appeared only later during the experiment and concerned
mostly weed density and diversity, while species composition was rather similar (see details in
the discussion of Manuscripts 3 & 4, chapter C.II). Such comparisons of several perennial
crop management factors are rarely reported in the literature.
While the field experiment provided much finer estimations of plant emergence, plant survival
and biomass production than the large-scale studies, other phases of the life cycles such as
seed production could not be directly quantified but only roughly estimated from the weed
biomass and the plant stages. Measurements of the weed emergence potential in the field by
superficial soil tillage at four dates during the experiment did not succeed, due to unfavourable
conditions for germination (lack of rain) at the chosen dates. Therefore, there is no evaluation
of the temporal development of superficial seed bank densities. The final weed seed banks
were studied by analyzing soil cores of all experimental plots with the direct germination
method (modified from (Wellstein et al., 2007) and (Cardina et al., 2002a). Unfortunately,
results of this analysis were not available for this thesis but will soon be published.
Future experiments should also test other management factors and treatment levels to account
for the existing diversity in agronomic practices. In particular, the use of crop species mixtures
(e.g., legume + grass) should be tested as they may provide even greater weed suppression due
to complementarities in growth dynamics and resources use as discussed in chapter C.II.4.4.
Moreover, the cutting dates should be adapted to crop growth dynamics and tested in future
experiments, as they might be even more important than the cutting frequency with fixed
common cutting dates (see C.II.4.4 for details).
D.I.4 Comparison of weed species reactions between the large-scale
surveys and the small-scale field experiment
When comparing the relative plant frequencies of individual weed species in the large-scale
weed surveys in the Chizé region and the small-scale field experiment in Epoisses, many
species showed quite similar behaviour in both studies (Fig. 21). Seven species had relative
preferences for PFCs in both studies, about 15 species showed relative preferences for annual
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