Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
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the simulation mo<strong>de</strong>l, although increasing the complexity of mo<strong>de</strong>ls increases the risk for<br />
over-parameterization, which may reduce the predictive robustness.<br />
Such mechanistic mo<strong>de</strong>ls (‘ALOMYSYS’ and ‘GENESYS’) have been <strong>de</strong>veloped by the<br />
weed research group (BGA) in Dijon (France). The ALOMYSYS mo<strong>de</strong>l simulates the<br />
population dynamics of Alopecurus myosuroi<strong>de</strong>s as affected by <strong>crop</strong>ping systems, and<br />
GENESYS is <strong>de</strong>dicated to the population dynamics and gene flow at the landscape level<br />
between different wild and cultivated rapeseed (Brassica napus) and beet (Beta vulgaris)<br />
varieties (Colbach et al., 2006a; Colbach et al., 2006b; Colbach et al., 2007; Sester et al.,<br />
2008). FLORSYS is a new mo<strong>de</strong>l currently un<strong>de</strong>r <strong>de</strong>velopment 19<br />
using basically the same<br />
principles, but simulating the dynamic of the whole plant community (several weed species<br />
and the <strong>crop</strong>), hence accounting for the differences in weed traits across the species, and for<br />
their contrasted response to <strong>crop</strong>ping systems (Gardarin et al., 2007a).<br />
The mo<strong>de</strong>ls simulate the plant life cycle, representing the state of the system <strong>with</strong> a daily time<br />
step, and the various biological and physical processes affecting seed germination, seedling<br />
emergence, seedling growth and <strong>de</strong>velopment, plant mortality and seed production (Colbach<br />
et al., 2007). Most processes involved in weed population and community dynamics may<br />
already be simulated by the plurispecific FLORSYS mo<strong>de</strong>l, including the impacts of soil<br />
tillage (types and dates) on seed distribution <strong>with</strong>in the different soil layers, the effects of soil<br />
temperature and humidity on seed germination, the effects of herbici<strong>de</strong>s on weed mortality,<br />
and competition <strong>with</strong> neighbouring <strong>crop</strong> and weed plants. However, the current versions of all<br />
three mo<strong>de</strong>ls account neither for losses of weed seeds due to predation nor for processes<br />
specific to perennial <strong>crop</strong>s, e.g. the impacts of repeated hay cuttings on weed and <strong>crop</strong> growth.<br />
In the current versions, the life cycle of all weed plants is interrupted at soil tillage after <strong>crop</strong><br />
harvest. Therefore, <strong>crop</strong>ping systems including perennial <strong>crop</strong>s cannot be simulated. The<br />
existing mo<strong>de</strong>ls must thus be exten<strong>de</strong>d <strong>with</strong> additional modules that simulate (i) the regrowth<br />
abilities of weed and <strong>crop</strong> plants after repeated cuttings and (ii) the impacts of seed predation.<br />
Knowledge obtained from this thesis might be used for supporting mo<strong>de</strong>l construction of postcutting<br />
weed and <strong>crop</strong> growth (see below). However, additional studies on weed seed<br />
predation are probably required before this complex ecological interaction between plants and<br />
animals can be formalized in a mechanistic way.<br />
19 http://www2.dijon.inra.fr/bga/umrbga/spip.php?article151 (accessed on 21 April 2010)<br />
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