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

perennial crop treatments, differences between spring and autumn sown crops were much
stronger than between the two cutting frequencies and the two crop species.
Results suggested that several stages of the weed life cycle were affected by three main
characteristics of perennial forage crops :
A) The absence of soil tillage was probably the main reason for i) reduced germination and
emergence rates in the perennial crops after the crop establishment phase, ii) increased
survival of established weed plants and probably also iii) reduced weed seed survival, as seeds
stay on the soil surface.
B) The strong and temporally extended competition of the perennial crops reduced vegetative
weed growth and seed production.
C) The frequent hay cuttings destroyed the shoots and reduced seed production of weed plants
that often showed lower regrowth and higher mortality rates than the perennial forage crops.
In contrast, weeds were not able to profit from temporally reduced competition for light after
hay cuttings.
The rather complex experimental design and the frequent observation dates permitted
disentangling some, but not all, of these mechanisms that acted often simultaneously, showed
reinforcing or compensating interactions and cumulative effects on the weed life cycle.
Key words: Plant population dynamic, temporary grassland, crop rotation, soil tillage,
competition, cutting, regrowth, Integrated Weed Management, biodiversity.
C.II.1 Introduction
Today’s crop rotations are frequently very short (2-4 years) and often constituted by crops that
provide rather similar weed growth conditions (e.g. only annual winter-sown crops).
Therefore, weed species adapted to the conditions in these crops may be favoured in every
year leading to high population growth rates which increases the need of intensive curative
(chemical or mechanical) weed control. However, these techniques may have strong negative
environmental side effects which are increasingly considered (e.g. groundwater pollution by
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