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 leaves (nee<strong>de</strong>d for photosynthesis) and buds (nee<strong>de</strong>d for regrowth) were <strong>de</strong>stroyed for<br />
species belonging to the latter groups. Moreover, results of the greenhouse experiments<br />
showed that the residual green surface remaining after cutting is correlated to the plants’<br />
regrowth speed (Article 4) and that broadleaved weed species have a higher probability to<br />
survive if the terminal buds are not <strong>de</strong>stroyed (unpublished results).<br />
2) In the greenhouse experiments, post-cutting regrowth was also better for perennial species<br />
compared to annual species. Besi<strong>de</strong>s their longer life span, perennial species might also<br />
have more belowground reserves of carbohydrates that may be remobilized for regrowth<br />
after cutting. Differences between these species functional types observed in the largescale<br />
studies (Article 2) are thus probably also caused by the impact of cuttings (and not<br />
only due to the absence of soil tillage).<br />
Results of the greenhouse experiments in 2007 and 2008 also suggested that the regrowth of<br />
weed plants a) increased <strong>with</strong> plant biomass before cutting (for plants of the same age), b)<br />
<strong>de</strong>creased <strong>with</strong> plant age, c) increased <strong>with</strong> cutting height for broadleaved species, and d)<br />
<strong>de</strong>creased <strong>with</strong> the number of previous cuttings (see Articles 4 & 5 and two master thesis of<br />
Henriot (2007) and Bonnot (2008) co-supervised by the present author. The impacts of plant<br />
age and cutting height roughly correspon<strong>de</strong>d to previous studies (El-Shatnawi et al., 1999;<br />
Andreasen et al., 2002), while the two other factors have rarely been investigated (Mager et<br />
al., 2006; Wilson et al., 2007). These observations on the interspecific variation of the<br />
regrowth ability may also be explained by the hypothesis postulating that the plant growth<br />
ability <strong>de</strong>pends on the amount of carbohydrate resources remobilizable from roots and<br />
stubbles to replace the <strong>de</strong>ficit caused by the absence of photosynthesis. An additional<br />
greenhouse experiment (presented in the co-supervised Master-I thesis (Bonnot, 2008) but not<br />
yet published in a journal), comparing the regrowth speed of cut plants <strong>with</strong> the initial growth<br />
speed of young uncut plants <strong>with</strong> the same (small) leaf area supported this hypothesis (Wilson<br />
et al., 2007). The observed higher growth speed of cut plants was probably caused by<br />
remobilisation of belowground resources. Moreover, cut plants may also profit from the<br />
bigger rooting system compared to younger uncut plants. Such additional knowledge about the<br />
effects of cuttings as a function of the plants’ regrowth ability may be useful for explaining<br />
and predicting the impacts of hay cuttings on arable weeds (see chapter D.III.2 for more<br />
<strong>de</strong>tails).<br />
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