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

C.II.3.1.3 Dynamics of individual weed species
While total weed densities showed increasing tendencies in annual crops and decreasing in
perennial crops, three groups of weed species can be distinguished by their reaction to the
different crop treatments (see Fig. 13 for an analysis per treatment and Fig. 14 for an analysis
per species). A first group of species showed increasing plant densities in all three annual
crop treatments. This group included 10 species: G. aparine, A. myosuroides, V. persica, S.
arvensis, F. convolvulus, P. aviculare, P. persicaria & P. lapathifolium, A. arvensis, and P.
rhoeas. Some additional species showed increasing densities mainly in the annual crop
treatment with OSFs (T10): L. multiflorum, B. sterilis, and G. dissectum. A second group of
species showed high plant densities in the spring-sown perennial crops after sowing in 2007
including 12 species: C. album, A. retroflexus, S. nigrum, S. asper, A. arvensis, C. bursapastoris,
E. crus-galli, Senecio vulgaris, T. officinale, P. persicaria & P. lapathifolium and S.
media. However, the densities of these species decreased strongly with time. While some of
them were no longer detected in both alfalfa and cocksfoot crops in 2008, others did not
completely disappear (or reappeared for some periods, mostly with low densities in 2008),
especially in spring-sown alfalfa. A third group of species emerged with high or medium
densities after sowing of the autumn sown perennial crop treatments. Nearly all of them
showed decreasing densities in most treatments, especially in cocksfoot regardless the cutting
frequency (T7 and T8), while seven species did not completely disappear from the alfalfa
treatments with a low cutting frequency (T2): A. myosuroides, V. persica, B. sterilis, L.
multiflorum, F. convolvulus, S. media, A. arvensis and four species remained present in the
alfalfa treatments with a high cutting frequency (T4): V. persica, F. convolvulus, P. aviculare,
and Sonchus sp. Three species (C. bursa pastoris, A. retroflexus, and V. arvensis) showed
strongly decreasing densities and were no longer detected at the end of the experiment in any
of the four autumn sown perennial crops. A. arvensis was the only species that showed low but
rather stable densities in all perennial crops. Finally, G. dissectum showed strongly decreasing
densities in all perennial crops, but did not completely disappear after 2.5 years ( Fig. 14).
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