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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Fig. 1: Illustration of possible interactions between the (negative) effects of cutting and<br />
competition on total biomass production of a weed plant. White boxes correspond to the<br />
reference (Ref.): biomass production of uncut plants <strong>with</strong> low competition. Striped boxes<br />
represent the cut plants, grey boxes plants experiencing stronger competition (comp.), grey<br />
striped boxes the combination of both treatments.<br />
A) A positive interaction arises when the (negative) effect of one treatment is<br />
disproportionally increased by the other treatment. In this case, the combined effect of both<br />
treatments is stronger than expected by the sum of the effects of the separate treatments.<br />
B) When combining both treatments, the two negative effects are simply ad<strong>de</strong>d up. Additive<br />
effects are thus indicated by the parallelism of the dotted lines.<br />
C) A weak negative interaction arises when the combined effect of both treatments is weaker<br />
than expected by the sum of the effects of both separate treatments.<br />
D) A strict negative interaction arises when the strong effect of one treatment (here:<br />
competition) is alleviated by the other treatment (cutting).<br />
Fig. 1: Illustration <strong>de</strong>s interactions possibles entre les effets <strong>de</strong> la fauche et la compétition.<br />
Total biomass<br />
A) Positive<br />
interaction<br />
B) Additive<br />
effects<br />
Ref. Ref.<br />
Ref.<br />
Uncut Cut Uncut Cut<br />
Weak comp. Strong comp.<br />
Uncut Cut Uncut Cut<br />
Weak comp. Strong comp.<br />
Treatment combinations<br />
121<br />
C) Weak negative<br />
interaction<br />
Uncut Cut Uncut Cut<br />
Weak comp. Strong comp.<br />
D) Strict negative<br />
interaction<br />
Ref.<br />
Uncut Cut Uncut Cut<br />
Weak comp. Strong comp.<br />
In this paper, we investigate the possible interactions between cutting and competition<br />
on the plant growth of several annual weed species. We do not know about any study<br />
explicitly studying the interactions between both effects on weed plants, except Graglia et al.<br />
(2006), who analyzed the combined effects of mowing and competition on the biomass<br />
production of the perennial Crisium arvense in the following <strong>crop</strong>. Data on the performance of<br />
annual weeds are completely lacking. We thus study an open question and do not have any a<br />
priori expectations concerning the sign of the interaction. Using a full factorial <strong>de</strong>sign, we will<br />
analyze the effects of cutting and competition alone and in combination.<br />
MATERIAL AND METHODS<br />
The interaction between cutting and competition was studied using 12 annual weed<br />
species (Table I). Seeds were purchased from Herbiseed (www.herbiseed.com). Plants were<br />
grown in 8 experimental trays (57*37*15cm) containing a mixture of ¼ potting soil, ¼ field<br />
soil, ¼ turf, and ¼ vermiculite. Each tray was divi<strong>de</strong>d into 4 parts, each <strong>with</strong> 12 precise<br />
positions for weed plants. The 12 weed species were randomly allocated to these positions.<br />
After sowing (17 Dec 2007, 2-3 seeds per position), seeds were stratified for 3 weeks in<br />
darkness at 4°C to break seed dormancy of some weed species (Milberg and An<strong>de</strong>rsson,<br />
1998). Trays were then put into a greenhouse (5-17°C), regularly watered using an automatic<br />
system and fertilized when nee<strong>de</strong>d. Seedlings were thinned to one plant per position. Trays<br />
were put outsi<strong>de</strong> the greenhouse on 9 May 2008.