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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the first year of the <strong>temporary</strong> <strong>grasslands</strong>. In contrast, species composition varied much less<br />
among 2-6 year old <strong>grasslands</strong>, which is consistent <strong>with</strong> observations by Critchley et al.<br />
(2006) in sown field margin strips in England.<br />
While the large-scale study <strong>de</strong>monstrates the effect of perennial <strong>crop</strong>s on weed communities<br />
in the following annual <strong>crop</strong>, future studies must also <strong>de</strong>termine how long this effect may last.<br />
Canadian farmers estimated that weed control benefits of PFCs lasted for one, two, and three<br />
or more years (11%, 50%, and 33% of respon<strong>de</strong>nts, respectively, Entz et al., 1995). While the<br />
large-scale studies allowed a good estimation of (instantaneous) species composition and<br />
species richness, abundance estimates were only based on one evaluation of the species<br />
frequencies on the 32 quadrats per field and per year, which is not very exact and strongly<br />
<strong>de</strong>pen<strong>de</strong>nt on recent weed control actions. Therefore, high numbers of fields were required to<br />
<strong>de</strong>tect the effects <strong>de</strong>spite this variability. Future studies may thus also take into account the<br />
variability in <strong>crop</strong> management practices. Some of these shortcomings could be addressed by<br />
the field experiment discussed below.<br />
D.I.3 Weed population dynamics un<strong>de</strong>r various <strong>crop</strong> management<br />
practices in the small-scale field experiment<br />
Regular monitoring of the weed vegetation during the 2.5-years field experiment in Dijon-<br />
Epoisses also showed contrasted weed population dynamics in annual and perennial <strong>crop</strong>s<br />
(chapter C.II, Manuscript 3). Differences in weed plant <strong>de</strong>nsities, diversities, biomasses and<br />
species composition were strongest between the annual and perennial <strong>crop</strong>s, before all other<br />
contrasts concerning the <strong>crop</strong> management practices (see C.II.4.1 and summary in Table 11).<br />
Many typical arable weed species showed <strong>de</strong>creasing plant <strong>de</strong>nsities in perennial <strong>crop</strong>s and<br />
increases in annual <strong>crop</strong>s (Fig. 13 and Fig. 14). Therefore, impacts of PFCs on weed<br />
communities observed in the field experiment are quite close to the large-scale weed surveys,<br />
<strong>de</strong>spite the differences between the two studies (see the next section D.I.4 for <strong>de</strong>tails). Results<br />
of the field experiment are broadly also in line <strong>with</strong> several of the previous experiments in<br />
other <strong>crop</strong>ping systems reporting weed suppression by PFCs (e.g., Schoofs and Entz, 2000;<br />
Bellin<strong>de</strong>r et al., 2004; Teasdale et al., 2004; Albrecht, 2005; Heggenstaller and Liebman,<br />
2006, and other studies reviewed in Article 1).<br />
Among the three perennial <strong>crop</strong> management factors tested in the small-scale field<br />
experiment, the sowing date (autumn vs. spring) had strongest impacts on weed species<br />
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