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

Table I: Species included in the experiment.
Table I: Espèces inclus dans l’expérimentation.
Scientific name Code An. French English
Adonis aestivalis L. ADOAE Adonis d'été Pheasants-eye
Alopecurus myosuroides Huds. ALOMY x Vulpin des champs Blackgrass
Amaranthus retroflexus L. AMARE Amarante réfléchie Common amaranth
Ambrosia artemisiifolia L. AMBEL Ambroisie Common ragweed
Bromus sterilis L. BROST x Brome stérile Barren brome
Capsella bursa-pastoris Medi CAPBP Bourse à pasteur Shepherd’s-purse
Centaurea cyanus CENCY Bleuet des champs Common cornflower
Chenopodium album L. CHEAL x Chénopode blanc Fat hen
Galium aparine L. GALAP x Gaillet gratteron Cleavers
Geranium dissectum L. GERDI x Géranium découpé Cut-leaved crane's-bill
Stellaria media (L.) Vill. STEME Mouron des oiseaux Common chickweed
Veronica persica L. VERPE x Véronique de perse Field-speedwell
Medicago sativa L. MEDSA Luzerne cultivée Alfalfa / Lucerne
An.: weed species used for interaction analysis.
We compared 4 experimental treatments by combining a competition and a cutting
factor, each with two levels (see below). Each modality was represented by two separate
trays and 4 target weed plants per species per tray (n=384 weed plants).
High and low competition levels were created by sowing lucerne plants in alternate
rows at a high density (>70 plants/tray) all around the weed plants in half of the trays, the
other half contained only weeds. Lucerne was chosen because it is known to have good
regrowth ability (Meiss et al., 2008) and to be highly competitive against weeds (Gosse et al.,
1988; Smith et al., 1989; Schoofs and Entz, 2000; Meiss et al., 2008).
For the cutting treatment, half of the trays were cut at an early date (25 March 2008),
the other half was left uncut until the first common cutting date (16 April). Each weed and
lucerne plant was cut separately at ~5cm from the soil surface using scissors. Plants with a
creeping morphology were lifted up and cut at 5 cm from the rooting point. To study the longterm
effects of cutting and competition on weed plants, trays were cut every 3-4 weeks from
April until December 2008 (see Fig 3 for cutting dates).
DATA COLLECTION AND STATISTICAL ANALYSIS
We evaluated the aboveground plant biomass at each cutting date. The cut shoots of
each individual weed plant were dried at 80°C for 48h and weighted. Lucerne dry weight was
not evaluated at individual plant level but for the whole trays.
The interaction between the early cutting and competition treatments was analyzed
comparing the biomass production per weed plant (cumulated up to the first common cutting
date, 16 April). We present only the biomass data for 6 weed species (Table I) that had the
most replicate plants to maximize statistical power. For the other weed species, numbers of
individuals were too low, which was either caused by low germination or high mortality rates.
Biomass data was log-transformed which improved normality and homoscedasticity of error
variance (graphical verification using diagnostic plots of error distributions).
We first used a global model including all 6 weed species (3-way ANOVA). As we
found significant interactions (p