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

impacts on several phases of the weed life cycle (see general introduction). One rather
unknown mechanism is weed seed predation, i.e. the consumption of weed seeds by animals.
Weed seed predation has very recently gained much interest in agronomic and ecological
research. It may have very strong impacts on weed population dynamics making it interesting
for Integrated Weed Management (Westerman et al., 2005). On the other hand, favouring
weed seed predation may be favourable to seed eating organisms and enhance farmland
biodiversity at several trophic levels.
In PFCs, weed seed predation might be favoured by three mechanisms. i) The absence of soil
tillage prevents weed seeds to be buried in the soil. Thus all newly produced weed seeds stay
on the soil surface where they are more accessible to seed predators. ii) Reduced applications
of pesticides in PFCs compared to annual crops may be favourable to predatory organisms. iii)
The permanent vegetation cover as well as the absence of soil tillage create a more stable
habitat that may be preferred by seed eating animals over annual crops. Weed seed predation
might thus cause parts of the differences in weed communities between annual and perennial
crops observed in the weed surveys in the Chizé region, the field experiment and in previously
published studies. Several experimental studies were conducted to investigate (1) whether
seed predation rates differ between common annual weed species and (2) to analyse the
impact of vegetation cover.
B.IV.2 Measuring weed seed predation
Weed seed predation was measured using ‘seed cards’ (Westerman et al., 2003a) consisting
by seeds slightly glued to sandpaper strips that were fixed on the soil surface with nails. Two
types of negative controls were used: (A) Seed cards were put into total exclusion cages
(boxes made from metal wire gauze with 1 mm × 1 mm mesh size) permeable to wind and
rain excluding any type of seed predator. (B) Presenting plastic beads instead of weed seeds.
Moreover, vertebrate exclusion cages (boxes made from metal fence wire with 12 mm × 12
mm mesh size) were used in the 2008 experiment to separate predation by vertebrates and
invertebrates (see Article 8).
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