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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Table 12: Factors differing between five <strong>crop</strong> treatment comparisons (as in).<br />
Factor<br />
Crop type Species<br />
96<br />
Treatment comparison<br />
Sowing<br />
season<br />
Cutting<br />
frequency<br />
Tillage in<br />
inter<strong>crop</strong><br />
Soil disturbance (superficial tillage, sowing)* An >> P<br />
D >~ M<br />
(roots?)<br />
Season = T+ > T-<br />
Aboveground vegetation disturbance<br />
(hay cuttings /<strong>crop</strong> harvesting)*<br />
P > An = A >~ Sp C+ >> C- T+ >~ T-<br />
Fertilisation (N-fertilizer vs. N-fixation) ≠ ≠ = = =<br />
Vegetation cover (competition for light)*<br />
≠ ≠ growth<br />
dynamics<br />
≠ growth<br />
dynamics<br />
≠ ≠ <strong>crop</strong><br />
establishm.<br />
C- > C+ =<br />
Allelopathy ?? ?? = = =<br />
* Impacts of these factors on the weed life cycle are <strong>de</strong>tailed in Table 13.<br />
C.II.4.1.1<br />
Plant <strong>de</strong>nsities<br />
Emerged plant <strong>de</strong>nsities and biomasses of many common annual weed species showed stable<br />
or <strong>de</strong>creasing ten<strong>de</strong>ncies in all perennial <strong>crop</strong> treatments. Such weed population dynamics<br />
may be surprising given the complete absence of soil tillage and specific weed control<br />
techniques in the PFCs. (Possible mechanisms of these <strong>de</strong>clines will be discussed below).<br />
Interestingly, reductions in weed abundances in PFCs were much more pronounced than<br />
reductions in species richness leading to improved diversity/<strong>de</strong>nsity-ratios ( Fig. 12) that may<br />
be useful for reducing the ‘weeds tra<strong>de</strong>-off’ (see § A.III.3 in the general introduction).<br />
In contrast, some weed species showed strongly increasing population sizes in the succession<br />
of annual <strong>crop</strong>s, as indicated by the increasing field emergence <strong>de</strong>nsities (Table 10, Fig. 12,<br />
Fig. 13) and weed biomasses (Fig. 17) during the 2.5 years experiment compared to the<br />
perennial <strong>crop</strong>s. These strong weed increases in the annual <strong>crop</strong>s are probably due to events of<br />
weed seed multiplication during the experimental period. It can not be explained by <strong>de</strong>nse<br />
background seed <strong>de</strong>nsities or the initial weed seed addition, which would be visible in all<br />
treatments of the randomized block experiment, which was not the case for any of the 16 sown<br />
species. In both spring-sown perennial <strong>crop</strong>s, consi<strong>de</strong>rable weed seed production occurred<br />
probably during the first month after <strong>crop</strong> sowing due to the slow initial <strong>crop</strong> establishment<br />
and the late first cutting (see discussion on the mechanism below).<br />
C.II.4.1.2<br />
Species composition<br />
Due to these heterogeneous weed population dynamics, species composition varied most<br />
strongly between annual and perennial <strong>crop</strong>s at the end of the experiment, ( Table 9). After the