Diversifying crop rotations with temporary grasslands - Université de ...

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