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

(hemicryptophytes and geophytes, Raunkiær, 1905) may be particularly favoured by the
absence of soil tillage due to e.g., their longer life cycles or vegetative reproduction.
D.II.2 Competition (B)
Temporally extended competition for growth resources in PFCs is partly an effect of the
absence of soil tillage permitting the establishment of dense plant canopies and rooting
systems of the perennial crop. Therefore, impacts of competition cannot be completely
disentangled from the impacts of soil tillage discussed above. Both factors may favour plant
species adapted to slightly later successional stages (later after the last disturbance of the
vegetation), thus more ‘K-selected’ species with slower growth, later reproduction, higher life
span, bigger final plant size, vegetative reproduction. In contrast, annual crops would rather
favour species adapted to earlier successional stages (earlier after the last disturbance) thus
more ‘r-selected’ species with a fast initial growth, short life cycle, reproduction by seeds, etc.
The impacts of competition were particularly visible in the field experiment, where crop and
weed biomass showed negative relationships especially during the first year. Treatments with
bad initial crop establishment showed high initial weed biomass and the increase in crop
biomass was accompanied by a decrease in weed biomass. While Clay and Aguilar (1998)
observed reductions in crop-weed competition in older perennial forage crops, there was no
sign that 2-6 years old alfalfa stands showed less weed suppression in the large-scale surveys
(Article 2).
D.II.3 Hay cuttings (C)
Large-scale weed surveys, field experiments and the specific greenhouse experiments
suggested that regular hay cuttings contributed to changes in the weed community
composition. The consequences of cuttings might depend on (1) the level of damage due to
cutting, and (2) the plant regrowth ability.
1) In the large-scale surveys (Article 2), the small-scale field experiment (Manuscript 3) and
the greenhouse experiments (Article 4), species belonging to the functional groups of
grasses and broadleaved species with rosettes or with a small and creeping morphology
performed better than broadleaved species with a tall, upright or climbing morphology
(including the most widespread and most noxious arable weeds such as M. annua, C.
album, F. convolvulus and G. aparine). The most likely cause would be that larger parts of
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