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

1) The absence of soil tillage and the high quantity of biomass in PFCs may also favour the
establishment of a weed-suppressive mulch (Wiens et al., 2006).
2) High vegetation cover (and mulch) also changes the light quality, temperature and
humidity on the soil surface, which impacts weed germination (Huarte and Arnold, 2003).
3) Weed seed survival on the soil surface might not only be reduced due to seed predation,
but also to seed decay.
4) Some perennial crops such as alfalfa (but also several annual crop species) might liberate
allelopathic compounds inhibiting weed growth (Xuan and Tsuzuki, 2002).
5) Finally, improvements in soil structure and fertility, reductions in parasites or diseases of
cash crops caused by PFCs might also ameliorate the growth and competitive ability
against weeds of crops following PFCs.
D.III PERSPECTIVES: PREDICTING THE IMPACTS OF PFCS
D.III.1 Mechanistic models
Predicting weed population and community dynamics as a function of cropping system is a
challenging issue due to the complexity of the system and the high number of interacting
factors linked to crops, crop management practices, soil and climatic parameters and the
diversity of weed species traits (Colbach and Debaeke, 1998). Mechanistic models simulating
the various processes and cumulative effects involved in weed population dynamics are
valuable tools for two main reasons. First, they have a heuristic value helping to better
understand the complexity of the system, to identify possible interactions between processes
and factors, and to rank the significance of the factors affecting the fate of the field/weed
system. Second, they might be used for simulating a variety of cropping systems (‘in silico
experiments’), helping to identify solutions for weed management problems, and to perform
ex ante evaluations of alternative cropping systems. In silico experiments might partly replace
cropping system field experiments that are difficult to perform because of the long duration
required for accounting for cumulative effects (Colbach and Debaeke, 1998). The mechanistic
representation of involved processes is also a means to provide a large domain of validity for
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