Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
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including exotic species (Palmer and Maurer, 1997; Jiang et al., 2007; Lanta and Leps,<br />
2008).<br />
• In our experiment, the cutting dates and frequencies followed the experimental plan of 3<br />
vs. 5 cuts per year <strong>with</strong> common cutting dates for all treatments (Table 6). This <strong>de</strong>sign was<br />
used to disentangle the cutting frequency from the other experimental treatments (<strong>crop</strong><br />
species, sowing date) and to avoid introducing other variables such as the exact cutting<br />
dates that may also be important for both <strong>crop</strong> and weeds growth. Cutting dates were thus<br />
not optimized to specific <strong>crop</strong> growth dynamics and phenological stages that differed<br />
between the <strong>crop</strong> species (Medicago and Dactylis), sowing dates and cutting frequencies<br />
(Fig. 18). It may thus be recommend to use a flexible cutting frequency and to adapt the<br />
cutting dates <strong>de</strong>pending i) on the phenological stage of the forage <strong>crop</strong>s to optimize the<br />
<strong>crop</strong> growth and to maximize <strong>crop</strong>-weed competition but also ii) on the phenological stage<br />
of the most noxious weed species to <strong>de</strong>stroy high weed biomasses and to avoid seed<br />
production. In the case of our experiment, the lower cutting frequency showed some<br />
advantages:<br />
o the Dactylis <strong>crop</strong>s produced significantly more biomass than un<strong>de</strong>r the high<br />
frequency (equal production for Medicago, Fig. 17),<br />
o very frequent cuttings may reduce the regrowth ability of Medicago <strong>crop</strong>s,<br />
However, the cutting frequency should also not be too low, which may increase the risk of<br />
high weed seed production and may lead to inferior forage quality.<br />
While the weed seed bank analyses gives a good indication of the long-term effects of PFCs<br />
on weed infestations, this should also be verified by long-term <strong>crop</strong> rotation experiments such<br />
as the studies of An<strong>de</strong>rsson & Milberg (1998) and Sosnoskie et al. (2006). Moreover, the<br />
findings may <strong>de</strong>pend on climate and soil conditions and must thus be repeated in other<br />
locations. While such huge studies were not possible in our case, the effects of the perennial<br />
and annual <strong>crop</strong>s on the weed infestation of the following <strong>crop</strong> will be tested on our<br />
experimental set up by a) analyzing the soil seed bank and by observing the weed vegetation<br />
in a following test <strong>crop</strong> sown on all experimental plots.<br />
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