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

succession of annual crops, three intercrop management options were compared, namely i)
conventionally tilled intercrops with bare soil in winter, ii) tilled intercrops with a cover crop
in winter (used to reduce nitrogen leaching) that may also change the weed growth conditions
(Liebman and Davis, 2000; Moonen and Barberi, 2004) and iii) untilled overwinter stubble
fields (OSFs) corresponding to an agri-environment scheme where the soil is only tilled at the
end of winter (Critchley et al., 2004; Marsall et al., 2007). In such OSFs, established weed
plants may benefit from the absence of soil tillage (as in perennial crops) but also from the
limited inter-plant competition, which may increase their seed output. This agri-environment
scheme may be favourable to farmland biodiversity, as plant residues and seeds remain at the
soil surface where it may be eaten by animals (Moorcroft et al., 2002; Orlowski, 2006).
This experimental design was used to analyse the temporal dynamics of the emerged weed
communities during the whole experimental period, concentrating on weed species
composition, weed plant densities, and biomass. Finally, the potential underlying mechanisms
are discussed, based on the weed population dynamics in the different experimental
treatments.
C.II.2 Methods
C.II.2.1 Experimental design
The field experiment was located at the experimental farm ‘Epoisses’ of INRA-Dijon in
eastern France (47°20’N, 5°20’E) with a semi-continental climate and a calcareous clayey
soil. Nine crop treatments were compared (T2-T11, see Table 6 for details). Treatments varied
first by the crop type, opposing a succession of annual crops: winter wheat (Triticum
aestivum)–spring barley (Hordeum vulgare)–summer soybean (Glycine max) and two PFCs:
alfalfa/lucerne (Medicago sativa) and cocksfoot/orchard grass (Dactylis glomerata).
Within
the perennial crops, treatments further varied by crop sowing season, opposing autumn sowing
(4 Sept. 2006) and spring sowing (27 April 2007), and by cutting frequency, opposing a high
frequency (5 cuttings per year, C+) and a low frequency (3 cuttings per year, C-) for the
autumn sown plots. Sowing and cutting dates are given in Table 6,
lower part. Cuttings were
performed at about 3-8cm height from soil surface using a forage mower adapted to the small
experimental plots that directly removed the cut biomass. Within the succession of annual
crops, three intercrop treatments were compared: treatment T9 with superficial soil tillage (5-
8cm) performed with a rotary hoe ‘rotavator’ after crop harvest (‘conventional’, bare soil
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