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

C.II.3.1.4 Effect of weed seed addition
During the first month of the experiment, field emergence rates were always much lower than
the densities of viable seeds added to the soil at the beginning of the experiment. However,
this ratio showed considerable differences between the weed species, separating three groups
of species (Fig. 15). Field emergence densities were about 2-5 times lower than sowing
densities for a first group of species including G. aparine, V. persica, G. dissectum, S. media,
A. myosuroides, and L. multiflorum. For a second group including C. bursa-pastoris, F.
convolvulus, and B. sterilis, emergence rates were about 10 times lower (thus 10-15%
emergence). For a third group containing the remaining 8 sown species, only 1-5% of the
sown viable seeds emerged during the 8 first month of the experiment (Fig. 15).
Emergence density
(seedlings m -2 )
10
8
6
4
2
0
GALAP
1:1 1:2
PAPRH
GERDI
ALOMY
0 10 20 30 40
Sowing density (viable seeds m -2 )
Fig. 15: Relation between weed sowing density and field emergence densities of 17 weed species.
See Table 7 for species codes. Field emergence are means (±SD) of maximum seedling densities on sown microplots
during the first 8 month of the field experiment. SD of sowing density corresponds to the variability of seed
viability tested in Petri dishes (cf. Table 7).
Comparisons of weed emergence densities on sown and unsown micro-plots showed that
weed seed addition increased the plant densities of all sown weed species (except C. bursapastoris)
during the first month of the experiment ( Fig. 16).
The initial positive effect of
sowing increased with time for three species (group 1 in Fig. 16 including A. myosuroides, B.
sterilis, and G. aparine, thus the species that showed strong population increases in the annual
crops). The positive effect of seed addition remained more or less stable for four species
(group 2 in Fig. 16 including V. persica, S. arvensis, L. multiflorum and P. rhoeas) and
89
VERPE
LOLMU
POLCO
BROST
CAPBP
VIOAR
SINAR
LAMPU CHEAL
STEME
POAAN
ANGAR
1 st group
2 nd group
3 rd group
AMARE
1:5
1:10
1:40