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

A, the ‘green area remaining after cutting for photosynthesis’, would be determined by the
cutting height and by the weed plant height and morphology (vertical distribution of leaf area).
Plant height and morphology will depend on i) the weed species (functional group) opposing
tall and upright weed species vs. small and creeping species, ii) the plant age and stage at
cutting date (very young plants are too small and therefore not touched by the cutting etc.) and
iii) the plant growth resources and growth conditions (optimal water and nutriment
availabilities may e.g. lead to bigger and taller weed plants, but high light availabilities may
lead to smaller plants compared to plants grown in shadow, see references in Article 4). The
FLORSYS-model already simulates the weed plant height and the vertical distribution of leaf
area as a function of the phenology, biomass and light environment of each crop and weed
plant on a daily timescale (Gardarin et al., 2007a). However, the temporally extended
competition in PFCs as well as the repeated cuttings and regrowth events may produce weed
plants that may differ in morphology compared to weed plants grown in annual crops, which
needs to be quantified by future studies and integrated in the current model.
B, the amount of ‘carbohydrate resources that can be remobilized for regrowth’, might be a
function of i) the weed species (functional group), ii) the plant age, iii) the plant biomass
before cutting, iv) the number of times and frequency the plant has previously been cut, and v)
external conditions such as the temperature determining the rate of biochemical processes.
Although previous experiments determined the absolute quantity of carbohydrates in plant
roots and stubbles (Klimes and Klimesova, 2002; Rodriguez et al., 2007), the ‘quantity of
carbohydrate that can be remobilized for regrowth’ (B) cannot directly be measured.
However, it may be implemented as a ‘theoretical variable’ in the model. According to the
experimental results on several weed species, this variable would be:
• negatively related to the plant age (Fig. 6 of Bonnot, 2008 and Fig. 4 of Article 4),
• positively related to the plant biomass before cutting for plants of the same age (Table 4 of
Henriot, 2007; Fig. 4 of Bonnot, 2008 and Fig. 3 of Article 4) [the belowground biomass is
approximated by the aboveground biomass, which is possible as both are often closely
related (Gedroc et al., 1996; Wardle et al., 2004)],
• negatively related to the number of previous cuttings (Fig. 2 of Article 4), and
• different between plant species functional groups (e.g. higher for perennials compared to
annuals, Article 4).
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