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

crops, some species including Poa annua showed an intermediate behaviour in both studies,
and only few species showed inconsistent reactions between the studies (see Fig. 21 for
details). This result is remarkable, as the two studies differed in several aspects. While the
Chizé study compared perennial alfalfa crops with six different annual crops (with various
sowing dates) inserted in various crop rotations with a big variability in crop management
practices (herbicides, soil tillage, sowing and cutting dates…) and in natural conditions in the
region, the Epoisses experiment compared only one succession of annual cereal crops with
two PFC species, alfalfa and cocksfoot, with different management practices (but all without
herbicides) and a rather homogeneous weed species pool (weed seed adding at the beginning).
For instance, the high frequencies of Echinochloa crus-galli (ECHCG) and A. retroflexus
(AMARE) in perennial crops of the Epoisses experiment (Fig. 21) occurred only in the springsown
and never in the autumn-sown perennial crops. Such weed species would probably find
good emergence and growing conditions in summer-sown annual crops which were not
included in the Epoisses experiment. Alopecurus myosuroides (AMOMY) was clearly
associated with the annual cereal crops in the Epoisses experiment. In the Chizé surveys, this
species appeared with equal frequencies in annual and perennial crops. Its frequency in annual
crops was probably lowered due to the fact that the six annual crops of the large-scale study
included also 3 spring/summer-sown crops, where this species rarely grows. However, the
reason why Veronica persica (VERPE) was associated with alfalfa in Chizé and with annual
crops in the Epoisses experiment is still unclear.
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