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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<strong>crop</strong> treatments, weed emergence was even more reduced in the Dactylis <strong>crop</strong>s even if this<br />
<strong>crop</strong> showed higher initial weed <strong>de</strong>nsities and higher seed production. In this <strong>crop</strong>, the soil<br />
surface was generally har<strong>de</strong>r and often intertwined <strong>with</strong> fine and <strong>de</strong>nse grass roots, while the<br />
soil surface in the Medicago <strong>crop</strong>s was looser and often wetter, and comprised less superficial<br />
roots (Medicago roots are known to grow <strong>de</strong>eper than Dactylis grass roots), which might have<br />
favoured weed germinations.<br />
C.II.4.3.2 Competition (B)<br />
Competition for common growth resources (light, water, nutrients) and space is probably the<br />
most important direct interaction between <strong>crop</strong>s and weeds. An established and <strong>de</strong>nse plant<br />
canopy can affect several important stages of the weed life cycle (see Fig. 20 and Table 13 for<br />
an overview). Germination rates may be reduced due to a lack of light stimuli and a modified<br />
light quality un<strong>de</strong>r the canopy (Huarte and Arnold, 2003). Initial seedlings growth may be<br />
affected due to a reduced availability of water and nutrients or allelopathic interactions (Xuan<br />
and Tsuzuki, 2002). After seedling emergence, competition (for light) is probably the most<br />
important factor <strong>de</strong>termining weed growth, biomass and seed production in arable fields of<br />
temperate <strong>crop</strong>ping systems. There are several indications that competitive interactions played<br />
an important role for weed (and <strong>crop</strong>) growth in our experiment:<br />
• When pooling all <strong>crop</strong> treatments, <strong>crop</strong> and weed biomass showed strong negative<br />
correlations for all measurement dates during the first year of the experiment suggesting a<br />
strong impact of competition (Fig. 19). In particular, the initial weed biomass was high in<br />
all treatments and plots, where the initial <strong>crop</strong> biomass and competitive ability was low.<br />
This was the case in the cocksfoot <strong>crop</strong>s, which generally showed a slower initial<br />
establishment than alfalfa and winter wheat (Fig. 18). Moreover, the autumn-sown<br />
perennial <strong>crop</strong>s showed a better establishment than the spring-sown perennial <strong>crop</strong>s. When<br />
these two ‘unfavourable factors’ were combined (spring-sown cocksfoot <strong>crop</strong>s), initial<br />
weed biomass was highest (Fig. 18) and in turn reduced <strong>crop</strong> growth due to competition<br />
during the first month. However, the initial competitive disadvantages of spring sowing<br />
and of Dactylis <strong>crop</strong>s disappeared already during the first year ( Fig. 18).<br />
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