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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composition that may be compared to the differences between spring and autumn sown annual<br />
<strong>crop</strong>s. However, these differences <strong>de</strong>creased <strong>with</strong> time in the emerged vegetation. In contrast,<br />
differences between the two <strong>crop</strong> species (alfalfa vs. cocksfoot) and the two cutting<br />
frequencies (3 vs. 5 cuts per year) appeared only later during the experiment and concerned<br />
mostly weed <strong>de</strong>nsity and diversity, while species composition was rather similar (see <strong>de</strong>tails in<br />
the discussion of Manuscripts 3 & 4, chapter C.II). Such comparisons of several perennial<br />
<strong>crop</strong> management factors are rarely reported in the literature.<br />
While the field experiment provi<strong>de</strong>d much finer estimations of plant emergence, plant survival<br />
and biomass production than the large-scale studies, other phases of the life cycles such as<br />
seed production could not be directly quantified but only roughly estimated from the weed<br />
biomass and the plant stages. Measurements of the weed emergence potential in the field by<br />
superficial soil tillage at four dates during the experiment did not succeed, due to unfavourable<br />
conditions for germination (lack of rain) at the chosen dates. Therefore, there is no evaluation<br />
of the temporal <strong>de</strong>velopment of superficial seed bank <strong>de</strong>nsities. The final weed seed banks<br />
were studied by analyzing soil cores of all experimental plots <strong>with</strong> the direct germination<br />
method (modified from (Wellstein et al., 2007) and (Cardina et al., 2002a). Unfortunately,<br />
results of this analysis were not available for this thesis but will soon be published.<br />
Future experiments should also test other management factors and treatment levels to account<br />
for the existing diversity in agronomic practices. In particular, the use of <strong>crop</strong> species mixtures<br />
(e.g., legume + grass) should be tested as they may provi<strong>de</strong> even greater weed suppression due<br />
to complementarities in growth dynamics and resources use as discussed in chapter C.II.4.4.<br />
Moreover, the cutting dates should be adapted to <strong>crop</strong> growth dynamics and tested in future<br />
experiments, as they might be even more important than the cutting frequency <strong>with</strong> fixed<br />
common cutting dates (see C.II.4.4 for <strong>de</strong>tails).<br />
D.I.4 Comparison of weed species reactions between the large-scale<br />
surveys and the small-scale field experiment<br />
When comparing the relative plant frequencies of individual weed species in the large-scale<br />
weed surveys in the Chizé region and the small-scale field experiment in Epoisses, many<br />
species showed quite similar behaviour in both studies (Fig. 21). Seven species had relative<br />
preferences for PFCs in both studies, about 15 species showed relative preferences for annual<br />
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